PORTLAND CEMENT 
ASSCC IATION, CHICAGO 


ON USE 


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Continuous 


HOLLOW GIRDER 


Concrete Bridges 


- PORTLAND CEMENT ASSOCIATION - 


Continuous 


HOLLOW GIRDE 
Concrete Bridge 


The activities of the Portland Cement Association, a nationa 
organization, are limited to scientific research, the development of 
new or improved products and methods, technical service, promotion 
and educational effort (including safety work), and-are primarily 
designed to improve and extend the uses of portland cement and 
concrete. The mantfold program of the Association and its varied 
Services to cement users are made possible by the financial support of 
over 65 member companies in the United States and Canada, engaged 
in the manufacture and sale of a very large proportion of all portland 
cement used in these two countries. A current list of member com- 


panies will be furnished on request. 


Published by 


PORTLAND CEMENT ASSOCIATION 
33 West Grand Avenue, Chicago 10, Illinois 


Foreword 


Specifications for concrete bridges in use today have been prepared 
with only the comparatively short-span bridge in mind. These specifica- 
tions have generally not made provision for bridges in which the dead 
load (a well-defined quantity) is a very large proportion of the load- 
producing stress—as in longer-span structures where the live load may 
be doubled with but slight increase in the final stress. There is a great 
need for authoritative specifications that will adequately cover long-span 
bridge design. 

Since current specifications require the same factor of safety for dead 
as for live load, the rapidly increasing ratio of dead to total design load 
due to increases in span length, places an economic limit on the span 
lengths of solid-section T-girder bridges. This has prompted search for 
ways to minimize the dead load stresses of these long spans, and develop- 
ment of the continuous hollow girder concrete bridge has provided one 
solution of the problem. 

The booklet Continuous Concrete Bridges* presents a simple method 
and procedure for the layout and design of continuous bridges having 
structural members with variable moments of inertia. For the sake of 
simplicity, that booklet is confined to a discussion of bridges with mem- 
bers having solid sections. The method presented, however, is adequate 
for the design of hollow sections also, providing the variation of the 
moment of inertia of a member closely approximates that for which the 
graphs for beam constants and fixed end moments were prepared. 

In order to present such special features of design and construction 
of hollow girder bridges as are unique to the type, and to demonstrate 
the application or the design methods set forth in Continuous Concrete 
Bridges to the hollow girder bridge, this booklet has been prepared. 

This booklet is, therefore, more or less a sequel or companion to the 
former publication and, since it is assumed that both booklets will be 
available to the designer, little of the material presented in the previous 
booklet that applies to the design of hollow girder bridges, is repeated 
here. Reference is made, however, to such material as is required. 


“Available free in the U. S. and Canada on request to Portland Cement Association 


Continuous Hollow Guirder 


Concrete Brid ges 


Section I—Introduction 


ARLIEST use of hollow sections for bridges was in long single spans with 
E short overhanging end spans which in reality were counterweights 
placed at each end, to produce large negative moments at the supports and 
small positive moments at mid-span. Many such bridges have been built, 
particularly in Europe. More recently this type of construction has been 
applied to long-span continuous bridges having three to five spans in a unit. 
In such bridges economic advantages are most pronounced. The Purdy Spit 
Bridge, Henderson Bay, Washington, shown on page 2, is a five-span 
structure of this type with the center span suspended between two canti- 
levers. The hollow girder deck is constructed integrally with hollow section 
piers. 

In general, the advantages of continuous bridges of the solid-slab and 
T-girder types discussed in Continuous Concrete Bridges are equally valid for 
the hollow girder type. The hollow section is merely a device to make verv 
long spans (longer than feasible with solid T-girder construction) eco- 
nomically possible. 

There is a minimum span length, dependent upon the allowable f. and 
other factors, at which the thickness of sections of hollow girders becomes 
too thin for economical, practical construction. Below this minimum even 
though the material quantities are less than for a T-girder of the same span, 
the cost of the hollow girder may be greater. 

Detailed computations for the design of a three-span continuous hollow 
girder bridge are given in the following pages. Application of the procedure 
presented in Continuous Concrete Bridges is worked out step by step and all 
important details entering into a complete design of this type structure are 
shown. The design of hollow girder bridges involving fixity at piers or abut- 
ments, hinged spans and variations in span lengths differing from those in 
the problem presented is accomplished by the general procedure given in 
Continuous Concrete Bridges. 


Section IIT — Layout and Loading 
Layout 


Special considerations for the layout of continuous concrete bridges have 
been discussed with particular reference to slab and T-girder types*. These 
same considerations are applicable to hollow girder bridges, but because of 
the greater span lengths involved certain modifications in the relationship 
between span lengths must be made. The selection of a suitable type of sub- 
structure will be limited, the lighter designs being unsatisfactory for this 
type of bridge. 

Figs. 1 and 2** show layouts based upon the considerations governing 
the layout of continuous bridges which will serve also as a basis for the layout 
of hollow girder bridges of two to four times the span lengths shown. 

Pile bents are not recommended because two or more rows of piles would 
be required at each bent, which likely would collect drift and cause an 
undesirable reduction in waterway. Open-frame bents, solid or hollow piers 
are preferred. Closed abutments are necessary in places where extension of 
over-all length to provide for open abutments is not practical. Wherever 
they can be used, open abutments are preferred. 

For hollow girder bridges or units of such bridges between expansion 
joints having interior spans not greater than 200 ft., the span ratio of 
1.0:1.40:...:1.0 is recommended. It will be noted that the ratio of interior 
to end spans is slightly greater than the lower value (1.37) recommended 
for T-girders due to the greater span lengths involved. For interior spans 
appreciably longer or shorter than 200 ft. some slight adjustment of the 
span ratios above or below that suggested will be found to give the most 
satisfactory and economical design. 

When the above span ratios obtain, the depth at the centerline of all 
spans should be the same and should be about 0.02 or 0.03 times the length 
of the interior spans. The deck depth at supports should be about 0.06 to 
0.08 times the length of the interior spans. It may be found desirable to 
increase slightly the depth over the center support of a four-span unit as 
compared with the depth at the first interior supports. These recommended 
depths are trial values; the most desirable ratios will depend upon the load- 
ing and unit stresses used. ‘The longer the spans the more desirable it will 
be to make the depth at the center shallow and at the supports large. 

When clearance requirements will not permit the desired depths at the 
supports, the depths may be reduced as much as one-third. If the depth is 
reduced it will be necessary to increase the thickness of webs and bottom 
slab and an increase in thickness of top slab may also be required. 


Loading 
The type of loading used in design of continuous hollow girder bridges 
in this booklet is identical with that used in the design of other continuous 
bridges}, which is the standard A.A.S.H.O. truck-train loading. For long- 
span bridges there is great need for a properly prepared specification covering 
*Continuous Concrete Bridges, pages 4 to 9. All references to Continuous Concrete Bridges are 
to the second edition of that publication. 


**Continuous Concrete Bridges, pages 8 and 9. 
{Continuous Concrete Bridges, pages 10 and 11. 


6 


loading and unit stresses. In the design that follows, for instance, trucks 
spaced as required by the A.A.S.H.O. are placed in the first and third 
spans to obtain maximum positive moment in Span 1. While this is conserva- 
tive, it is a condition not likely to obtain on the structure. 

Since the maximum loading permitted by most states on the highway 
system is less severe than H-15, and because of the high dead load to live 
load ratio obtaining for long-span concrete bridges, structures designed for 
H-15 loading will be more than adequate to carry safely any loading that 
may pass over them. In urban industrial centers it may be desirable to 
design for loadings greater than H-15. 


Section IIT — Design Method 


The method of design followed in this booklet is identical to that in 
Continuous Concrete Bridges as presented in Section IV of that publication. 
The formulas for final moments in Tables I and II* are applicable to any 
type of variation of J;, being simply the summation of series resulting from 
an infinite number of cycles of moment distribution. The curves for beam 
constants and fixed end moments** are sufficiently accurate for hollow 
girders unless the variation in J; departs materially from i, = 


Dx\ 2718 
if f +r (: _ 7) | on which the curves were based. J,=the moment of 


inertia at any point, x, measured from the left support; J; = the moment 
of inertia at the centerline of span; and 7 = the ratio of the moment of inertia 
at the support to the moment of inertia at the centerline of span. 


Section IV— Design Procedure 


Before starting the design cf a hollow girder bridge, it is necessary to 
decide upon the form of section desirable and suitable for the site. Having 
tentatively chosen the span layout and type of cross section, a systematic 
and logical sequence of design operations will minimize the work of calcula- 
tion. When studying this section of the text, reference should be made to 
the design problem which follows as it will help clarify the different steps 
and will show how each is carried out in practice. 


1. Select Girder Web Spacing and Design Slab 


In general it will be economical to use a wide spacing of girder webs 
with comparatively large depths, if headroom permits, say 8 to 12 ft. Fig. 45, 
Continuous Concrete Bridges, may be used to find design moments for roadway 
or top slab for web spacings up to 11 ft. 6 in. For the design of the roadway 
slab the thickness of girder webs should be assumed at about 6 in. 


2. Select r Values 


The r values throughout Continuous Concrete Bridges represent relative 
depths of sections at centerlines of spans and at supports for solid sections; 
thus when either the depth at the centerline or the depth at the support is 


*Continuous Concrete Bridges, pages 16 to 19 inclusive. 
**Continuous Concrete Bridges, pages 20 to 32 inclusive. 


known, the other can be found by use of the corresponding r value. For 
other than solid sections the r values merely represent the relationship of 
the moment of inertia at the centerline to that at any other section and can- 
not be used directly to determine depths. In other words 7, in the case of 
hollow girders or T-girders, is simply a measure of the magnitude of the 
variation of the moment of inertia. A parabolic variation was used in 
Continuous Concrete Bridges and this type of variation has been retained in 
this booklet, which makes it possible to use the curves for carry-over, stiffness 
factors, fixed end moments and deflections given in the former publication. 

Because the span lengths of hollow girder bridges will be greater than 
for T-girder bridges, the r values for the former will be somewhat greater 
than those suggested for T-girders*. When the length of interior spans is 
more than 200 ft. it will be desirable to increase r at each side of the interior 
supports of a three-span unit and at the first interior supports of a four-span 
unit to 1.6 or 1.7, while at the center support of a four-span unit a value 
of 1.8 for r is suggested. For spans between 140 and 150 ft. (about the upper 
limit for solid-web T-girders) and 200 ft., it is advisable to use r values inter- 
mediate between those suggested for spans over 200 ft. and those used for 
T-girder spans. The free end of end spans should have an r value of 0.5 to 0.7. 


3. Assume Dimensions at Centerlines of Spans 


For the span ratios recommended in Section II and for design stresses 
of f; = 18,000 and f. = 0.40 f’., assuming a 3,000-lb. concrete, the depth 
at centerline of all spans of a unit should be about 1/40 or 1/45 of the interior 
span length. The minimum thickness of girder webs and bottom slab at 
the centerline will be governed largely by practical considerations and 
should not be less than 6 or 7 in. except in unusual cases. 

Having selected a centerline depth, find the depth at the supports to 
satisfy the r values selected under Step 2. If clearance permits these depths, 
the design may be completed in the sequence of the steps that follow. If the 
depth at supports should be too great for clearance requirements, it will be 
necessary to increase the thickness of webs to 10 or 12 in. at supports by a 
straight taper from the centerline, and the bottom slab should be thickened 
to about the same thickness as the webs by placing the top surface on a 
flatter parabola than the bottom surface. It may also be necessary to thicken 
the top slab, in which case it is recommended that the thickness be main- 
tained uniform from the centerline to about the quarter-point and then 
tapered in the next 10 to 20 ft. to the maximum thickness. The moments of 
inertia at supports should be made as nearly as practical equal to (1 + 7)8J<. 
It is advisable to calculate and plot the moments of inertia of the gross con- 
crete section, and to plot the theoretically required variation of moments of 

Deas 


inertia; J; = [, E +r (: = 7) | . If the deviations of actual from theoret- 


ically required moments of inertia are small, proceed with the design up to 
and including Step 7. 


4. Draw Influence Lines for Moments at Supports 
See discussion under Step 2, Continuous Concrete Bridges, page 38. 


*Continuous Concrete Bridges, page 60. 


8 


5. Determine Maximum Live Load Moments at Critical Sections 
See discussion under Step 3, Continuous Concrete Bridges, page 38. 


6. Determine Dead Load Moments 


Find dead load moments in terms of undetermined constants as outlined 
under Step 4, Continuous Concrete Bridges, page 39. 


7. Check Assumed Sections 


Depths at centers of spans and at supports were tentatively selected under 
Step 3 above and thicknesses of members were assumed. Actual dead load 
moments may be determined at these critical sections based upon the as- 
sumed dimensions by substituting values of w, W,,, Wye, etc., in the dead 
load moments found in Step 6; add these moments to the live load moments 
found under Step 5 and check the assumed sections against allowable 
working stresses. If the chosen sections are inadequate or are too large, 
return to Step 2 for complete revision of sections. If the dimensions chosen 
under Step 2 do satisfy the combined moments just found, complete maxi- 
mum moment curves. 


8. Maximum Moment Curves 


Sufficient data for curves of maximum moments may be obtained by 
finding maximum moments at a few selected points. See discussion under 
Step 6, Continuous Concrete Bridges, page 39. 


9. Maximum Total Shears 


It will, in general, be sufficiently accurate for design purposes to find 
shears at points mentioned under Step 9, Continuous Concrete Bridges, page 64. 


10. Select and Arrange Reinforcement 


The main longitudinal girder reinforcement should be distributed over 
the full width of the tension flange, that is, from center to center between 
girder webs. If the number of bars required should result in a too close 
spacing when all bars are placed in one layer, the excess may be concen- 
trated in the web in a second and a third layer if necessary. Should it be 
necessary to put any considerable amount of the main reinforcement in the 
web its influence on the effective depth should be taken into account. 

In the deep, thin sections of hollow girders there will be an appreciable 
depth of stem below the top slab over interior supports which will be sub- 
jected to considerable tensile stress. Although this stress is within the modulus 
of rupture strength of the concrete likely to be used in such structures, as 
can be shown by analyzing the member as an uncracked section, it is still 
considered advisable to provide some extra longitudinal reinforcement in the 
webs unless inclined stirrups are used for diagonal tension reinforcement. It is 
important to maintain the integrity of the roadway slab over the piers and 
since concrete will sustain a considerably higher tensile stress with reinforce- 
ment than without, the introduction of a small amount of extra reinforce- 
ment at sections of high negative moment is justified. It is recommended 
that the additional reinforcement placed in the girder webs be spaced at 
about 4-in. centers below the bottom of the slab. The area of this reinforce- 
ment should be not less than 10 per cent of the main reinforcement and 


9 


should not be deducted from the main steel because it is relatively ineffective 
in resisting the moment at the support. This added reinforcement should 
extend about one-tenth of the span on each side of the support. 

A nominal amount of reinforcement should be provided in the top of 
the top slab and bottom of the bottom slab as a continuation of the main 
reinforcement though not necessarily required by moment calculations. This 
reinforcement should be about 0.20 to 0.25 per cent of the cross-sectional 
area of the slab. 

Longitudinal reinforcement in the bottom of the top slab should be pro- 
vided equal to 75 per cent of the maximum transverse steel to provide for 
moment in that direction. 

It will be noticed in the following design problem that diagonal stirrups 
are used. By so doing it is unnecessary to provide the additional steel in the 
girder webs as discussed above. Moreover, it has been found by tests made 
by the National Bureau of Standards that diagonal compression stresses are 
approximately half as great in concrete members with inclined stirrups as 
in those with vertical stirrups*. Therefore it is recommended that inclined 
stirrups be used aside from the fact that they are more efficient in resisting 
diagonal tension stresses. 

Tests have further shown, for all grades of concrete and yield point 
strengths of web reinforcement, that an appreciable amount of the total 
shear as diagonal tension is carried by the concrete, even though cracked. 
Bureau of Standards tests showed carrying capacity of the concrete to be as 
much as 50 per cent of the total load when small percentages of web reinforce- 
ment were used. It was also shown that unit shearing strength of a member 
is v=(0.005 + r) f,, when r=per cent of web reinforcement and f, is the 
yield-point stress of the steel. In the problem that follows, using a working 
stress of f; = 20,000 p.s.i. in the stirrups, the ultimate shearing strength will 
be of the order of 600 to 700 p.s.i. It is therefore apparent that the factor 
of safety in diagonal tension against an increase in live loads is more than 10. 

In view of the above consideration and almost universal requirement of 
specifications that when v exceeds 0.06 f’, web reinforcement be provided to 
carry the total shear, it is recommended that such reinforcement be designed 
on the basis of 20,000 p.s.i. and that a maximum allowable unit shearing 
stress of 0.12 f’, be permitted. 

The arrangement of reinforcement in hollow girders depends largely upon 
the concrete placement procedure. If the whole of the bottom slab is placed 
from end to end of the bridge or in the unit between expansion joints it would 
be necessary to place all web reinforcement before any concrete could be placed 
unless the stirrups were spliced at the tops of the bottom slab fillets. There 
is no reason why this should not be done. The regions of maximum shear 
are near the piers where the bottom slab is in compression and where there 
is more than adequate bond distance between the neutral axis and the top 
of the fillets. On the other hand, laps near the bottom slab would be in the 
tension zone between points of contraflexure within a span, but in this region 
stirrups can be welded if specifications do not permit splices. Splicing of 


*Shear Tests of Reinforced Concrete Beams by W. A. Slater, A. R. Lord and R. R. Zipprodt. 
Technology Papers of the National Bureau of Standards, No. 314. Government Printing 
Office, Washington, D. C. 


10 


stirrups as suggested admits a greater duplication in lengths since variation 
in laps may be made, provided they are never less in length than the re- 
quired minimum. 


11. Compute Deflections 


As a final step in the design, deflections due to dead load should be 
computed and the deflection curve should be shown on the working draw- 
ings so that camber opposite the deflection of the deck can be built into the 
structure. Deflections can be computed readily by the procedure given in 
Continuous Concrete Bridges, pages 77 through 90, using coefficients taken from 
the curves of Figs. 59 through 63e of that booklet. 


DESIGN PROBLEM 


A crossing is assumed which, allowing for end slopes running through 
open abutments, requires a length back to back of abutments of 445 ft.; 
a 52-ft. roadway, two 4-ft. sidewalks, and a 3-ft. separation curb; minimum 
main span allowable to be not less than 175 ft. With this span restriction, a 
three-span continuous concrete hollow girder was chosen with spans 130 ft., 
182 ft., and 130 ft. as shown in Fig. 1. 


Fig. 1. Span layout for Design Problem. 


For design, a section including the top and bottom slabs from center to 
center of adjoining cells and one web, making an I-section, may be con- 
sidered isolated and treated as an independent unit extending the full 
length of the bridge. The deck is assumed to be freely supported and sub- 
jected to A.A.S.H.O. H-15 truck-train loading; 10-ft. traffic lanes; f, = 1,200 
p.s.1.3 fs = 18,000 p.s.i. 


SAGE 


== = = =F >| 
MSiruminous rilled joint | Poa 

with water stop TTS Roadway 
> 5 


Variable 
7 "tol" 


Variable 
4'3" fo 12-8" 


*) Variable 


F's} G"to 10" 


Fig. 2. Typical transverse section of four-lane divided highway bridge with sidewalks. 


1A 


Step 1. Select Girder Web Spacing and Design Slab 


The cross section, Fig. 2, shows that an 8-ft. spacing of girder webs pro- 
vides a well-balanced arrangement for the given conditions. 


Design of Roadway Slab 


Slab span = 8 ft. 0 in. — (12 in. + 7 in.) = 6 ft. 5 in., assuming a 7-in. 
girder web. 

By means of Fig. 45, Continuous Concrete Bridges, page 61, the maximum 
moment in the slab can be obtained and the dead load moment can be com- 
puted assuming a 7-in. slab: 


Live load plus impact moment = 0.308 X 12,000 = 3,700 ft.lb. 
Dead load moment = 0.10 X 88 X 6.42? = 360 ft.lb. 
4,060 ft.lb. 

4,060 X 12 


18,000 X 0.87 X 4.7 
Use 54-in. round bars at 514-in. centers, 2 in. clear of top of slab. 


4,060 X 12 ' 
Bottom steel = 18,000 X 0.87 X 5.2 = 0.60 sq.1n. 

Use 5-in. round bars at 6-in. centers, 1% in. clear of bottom. 

Longitudinal bottom reinforcement to be placed between fillets equal to 
75 per cent of transverse reinforcement in the same plane amounts to 5¢-in. 
round bars at 8-in. centers. Longitudinal top reinforcement to be nominal, 
Y-in. round bars at 12-in. centers, except in the areas where main-girder 
tension reinforcement is required. See Fig. 11 for slab reinforcement. 


Top steel = = 0.66 sq.in. 


Step 2. Select r Values 


For the span lengths proposed, an r of 1.5 at pier ends and 0.5 at free 
ends of spans should be satisfactory, 1.e., 


TAB = 1Ypec = ieee LBA = Be — CB CDA iS. 


Step 3. Assume Dimensions at Centerline of Spans 


Trial dimensions for centerline of spans (Fig. 3a): 


Top slab 7 in. (computed under Step 1) 
Girder web 7 in. 
Bottom slab 6 in. 


Over-all depth 4 ft. 3 in. (approx. 1/43 of Span 2) 
Determine the gross moment of inertia of this section. 


Center of gravity: 
7 X 96 = 672 672 X 47.5 = 31,920 
6X 9= 54 54 42.0 2,268 
7 X 38 = 266 266 X 25.0 = 6,650 
Ger? 
6 X 96 


= 54 hea eR 432 

= 576 576 X 3.0 = 1,728 

1,622 in.? 42,998 + 1,622 = 26.5 in. from 
bottom to c. of g. 


Az 


[hire ho 


Cle Ay mae ro ey 4a a See = Lee S Va eira) en a 


O.1Ol2 SES) CEASE 
pea | hOneSe sate Ci 


(b) Section at piers. (c) Section at outer end of end spans. 


I. (moment of inertia at centerline): 


96 (73? +63 
Slabs: ee ) ay Oe 
G12) xe2 12 =e2 90,552 
516 25554 8 BOLO 
9 63 X 4 
Fillets: ae = 216 
54 (15.52 + 18.5?) e455 
i 383 
Web: a = 32,008 
266i» = 599 


I, = 683,198 in.4 
Moment of inertia required at piers = 

(i +7)3Z, = (1 + 1.5)3 X 683,200 
Moment of inertia required at free ends = 

(1 +1r)*J, = (1 + 0.5)3 X 683,200 = 2,306,000 in.‘ (Eq: 2) 
Assume thickness of top slab remains constant; that webs increase in thick- 
ness linearly from 7 in. at center of span to 10 in. at piers, and that bottom 
slab increases parabolically from 6 in. at center of span to 10 in. at piers. 
With these dimensions it will be found that a 12 ft. 8-in. depth at the interior 
supports (Fig. 3b) gives a moment of inertia of 10,803,000 in.4 or an excess 


10,675,000 in. — (Eq. 1) 


13 


of 1.2 per cent over theoretical requirements (Eg. 7) which is close enough. 

If the moments of inertia at two or three sections between the centerline 
of span and the supports are now computed, a curve showing the variation 
of the actual moments of inertia throughout the span can be plotted and 
compared with a curve representing the theoretically required values of 


D Zals 
I ak f +r (: — 7) | (see Fig. 4). Curve B can be used to select a 


cross section for the free end of the end spans since the section at that point 
should be about the same as the section between the centerline and the 
interior support, which has the same moment of inertia as that required at 
the free end, namely, 2,306,000 in.‘ (Eg. 2). The section closely meeting 
this requirement is at 0.22Z from the support and is shown in Fig. 3c. Its 
moment of inertia is 2,306,000 in.4. 


} 


supa Niet tebge ge T 


i 
} if ' 
etl anecend Kener aere be ealaaen jeseieee dana anaes RSH A ewe 


A-Theoretical Ix curve for toot ae in4 
when Iy= Ic [141.5 (1-4)? ] 
B- Actual Ix curve for hollow girder 


of Design Problem 
cbedeuke son shun bose lonene 


{ 


oe te ea ne 


Moment of Inertia in Inches 4 


14 


Step 4. Draw Influence Lines for Moments at Supports 


To draw influence lines for support moments take beam constants and 
fixed end moments from curves in Contenuous Concrete Bridges, pages 20-32: 


For ra = 0.5 and rg = 1.5 (Figs. 5* and 6*): 

Cap = — 0.836; Cra = all Katey 6 kpa = 13.55 
Forra = rp = 1.5 (Figs. 5* and 6*): 

Cac => Cos => —0.745; Kec = keg = 17.10 


ta 


K 1—0.836 X0.556) 13.55 
Fen (ras (O'ond 1; pase 152) = ZOE Sy 73 
DK 17.10 


Dgc = Dep = 1.00 — 0.373 = 0.627 


Load in Span 1: 


Mea = Mpc = Mz = a Ms (page 17*) 
= Sy eae B (Eq: 3) 
To 07218 
Mcp = Men = Mc = ee (page 17*) 


Load in Span 2: ) 
1—Dzgc) ME,—Cos Des (1—Dac) ME 
Mpa = Mpc = Mp = ( se) Mize ~ oe Bo) Mog 
cs OOM ar 0145.0, 62a x OS TSM eS 
0.782 
OAM ae 0.2252, (Eq. 5) 


Mcs = Mcp = Mc = 0.477 ME, + 0.223 ME, (by symmetry) (Eq. 6) 


(page 17*) 


Load in Span 3: 
Mpa = Mac = Mz = SVE) M; (Eq. 7) 
Mer == Mep = Me —- On525 M; (Eq. 8) 


Ordinates for influence lines for final distributed moments at supports 
can be computed now by substituting in Eqs. 3 to 8 fixed end moments 
taken from Figs. 7 to 15**. These values are tabulated in Tables I and II 
for a load P placed at each tenth point of each span. Influence lines for Mz 
and Mc¢ can now be drawn as shown in Figs. 5 and 6. 


*Continuous Concrete Bridges. 
**Continuous Concrete Bridges, pages 22 to 30. 


i 


Table I—Ordinates for Influence Lines for Moments at Supports 


Load in Spans 1 and 3 


Load in Span 1 Load in Span 3 


Mip** | Ma, Ms 
(Eq. 1 (Eq. 3 Mp Meo Mp Meo 
(Figs.7-15 *)|(Figs.7-15*)| page 17*) | page 17*) | (Eq. 3) (Eq. 4) (Eq. 7) (Eq. 8) 


—086PEL | —.012PL | —.084PL) | —.098PL3 | —.044PL, | 019 PE 022 en es 
BL S9 — .047 =e OS —.186 .085 +.036 +.041 UOT ee 
JY, — AOL —.234 soll ele +.052 05) aioe es 
147 —.164 = fAehi/ = 408 150 +.064 +.068 =—.158 “ 
att = AIG Sails) =58)Il3) .164 +.070 1-020 —.164 
.071 —.244 = FN) — E201 e158 +.068 +.064 SED) 

— .036 == fxlel) = JBI — .234 .134 = ODI ci OZ Stee? 

= (0 —.174 aloo =lOS 507 +.041 +.036 OOo 

— .003 = 095 = OYE — .084 = {05 +1022 +.019 —.044 


CeUANURONE 


SPAN | 


Méc Mop Mp Me 
Si (Figs. 7-15 *) (Figs. 7-15 *) (Eq. 5) (Eq. 6) 
Fi —.093PL, —.005PLs —.045PL» —.023PL2 
io —.168 “ 02500 —.085 “ —.048 “ 
3 =211 4 —.059 « —.114 “ — 075.4 
4 —.214 “ Sa ky & =127 4 1102 0" 
5 LA ULO & Sayre —.122« a2 12206 
6 = id ae Sate == 10205 AVA be 
a) —.059 “ = 241 06 —.075 “ —114 4 
8 —.023 « —.168 ¢ ==043 5% —.085 “ 
x) —.005 “ =,093. * 029%" —.045 “ 


*Continuous Concrete Bridges. 

**Subscripts AB and BA correspond to subscripts in Figs. 7-15 (Continuous Concrete Bridges) and the 
moments are the fixed end moments at the left and right ends respectively of Spans 1 and 3 when the 
proper values of L are used. 


a 
16 


| i 


: ; i 3 U H : 1 L i 
INFLUENCE LINES FOR Mpa 
vg dhe pots Pp 


USE LOF SPAN IN WHICH LOADIS PLACED 
MOMENTS ARE-FOR LOAD IN SPAN | AND 2 
MOMENTS ARE+FOR LOAD IN SPAN 3 


i { 
Nef te t 
t 
{ 


Mea in terms of PL 


Fig: 


Step 5. Determine Maximum Live Load Moments at Critical Sections 

For maximum positive live load moment in Span 7, first load Span 3 with a 
truck-train so as to produce maximum positive moment at B. This is found 
to be when trucks are placed as shown in Fig. 7. 


From Fig. 5: 
Mz = (0.063 X 3 + 0.064 X 0.75 +0.070 X 4+0.067 X1)P X 130 
= 75.9P 


In order to find the point of maximum combined dead and live load 
moments in Span1 it will be necessary to find the live load moment at 


L7. 


9 


Mc in terms of PL 
: eae q 


USE LOF SPAN IN WHICH LOAD IS PLACED 

MOMENTS ARE + FOR LOADINSPAN I 

MOMENTS ARE - FOR LOADIN SPAN 2 AND3 
i ‘ (teeaty 


ee ee ee 


Fig. 6. 


several points in the vicinity of the section of maximum combined moment 
which experience indicates will be between 0.30Z, and 0.35L;. When Wheel 
9 of the train is at 0.30L;, again using Fig. 3, 


Mp = (— 0.149 X 0.75 — 0.122 K 4 — 0.152 KX 1—0.150 X3)P X 130 
Sal 6.27 


and the positive moment under Wheel 9 is 


M301, = 5.36P X 0.30 X 130 — 30 X 0.75P — 0.30 (156.2 — 75.9)P 
= 162.4P 


18 


#7 #8 #9 FIO Hy #12 #| #2 #344 #546 
3P ISP APP 3P I5P 3P ISP app 3P ISP 
QA Oo Qo D 


COQ Qo Ole 
iasty [ia 30° [1a 30° ha’ 


4513 


Fig. 7. Loading for maximum positive moment in Span 1. 


Similarly M331, = 168.1P 
M351, = WA PAL 


in which P = 6,000 X 0.8 (1 SF 


M301; = 880 ft.kips 
M331, = 911 ft.kips 
M.as1, = 933 ft-kips 


50 


|| = Dy 
aon) rere 


WHEEL *#] #2 #3 #4 45 4#6 #7 #8 «#9 #10) «6B #12) HR HY 
3P ISP 3PI5P 3PI5P 3P ISP AP P 3p I5P 3P TSP. 


AEO)C) Owe Otol lOuenL OMe Ohis OVO 
TN Liat] 30" Jie 30° fae] hor] | 30° Ja’ 30° fia] 30" [a 


ios 


Fig. 8. Loading for maximum negative moment at Support B. 


For maximum negative moment at B place loads in Spans 1 and 2, trying 
them in a few positions until the one is found which gives maximum moment. 
For this problem that position is shown in Fig. 8 and 


Die elle 3°). 303 05) P x 130" 0:193 x3 
— 0.185 X 0.75 — 0.123 K 4 — 0.127 X 1)P X 182 


= — 394.0P 
Be ME = 60001 0.8 (ae 8 | 15 1960-1 
in whic = 6, : PLT) eee 5 
Mz = — 394.0 X 5,360 = — 2,111 ft.kips (Eq. 10) 


The maximum negative moment at C’ will be the same as at B by sym- 
metry when the truck-train is headed in the opposite direction. 


WHEEL #) #2 #344 #546 #7 #Q 
3P15P 3P.15P 4PP 3P 75P 
a BOO Oo OO Oo Cc D 
3 Mal 30" fia] 30° ya] 30° [ra 


Fig. 9. Loading for maximum positive moment in Span 2. 


|b! 


For maximum positive moment in Span 2 place the heaviest wheel in the 
train at centerline of span and other wheels of the train will be located as 
shown in Fig. 9. The moment under Wheel 5 will be 


M sor, = (1.017 X3+1.246 X 0.75 +0.500 X4-+0.577 X 1)P K 0.5 XK 182 
—14P—443P—58 X0.75P +0.5 (—1.274 —1.269)P X 182 


= 176.4P 
eee: 50 
in which P = 6,000 X 0.8 (1 oe aris) = 5,580 lb. 
M. sory = 176.4 X 5,580 = 984 ft.kips (Eq. 11) 


Step 6. Determine Dead Load Moments 


Find dead load moments at B and C considering each span loaded suc- 
cessively by substituting the fixed end moments due to the uniform load w 
and the haunch loads W in the formulas in Table I*. 


For uniform load w in Span 1: 


M*3 = — 0.078wL? ME, = — 0.129wL? (Pig: 16, pages 
and by Eq. 1, page 17*: 

M, = — 0.129wL? — 0.836 X 0.078wL? = — 0.194wL? = — 3,280w 
Similarly for haunch loads Wag and Wg, in Span 1: 

M", = — 0.0144W asl} ME, = — 0.0047WapL? (Fig. 77, page 32*) 

M"p = — 0.0015We aL? M3, = — 0.0178WeaLt (Fig. 77, page ge) 
and again by Eq. 1, page 17*: 

M, = — 0.0047WapL? — 0.836 X 0.0144W 4eL*® — 0.0178 We aL? 


— 0.836 X 0.0015We4Ll? = — 283Wap — 322Wea 


The coefficients of 14; determined in Eqs. 3 and 4, page 15, may now be 
multiplied by the values of M, just obtained to give the final distributed 
moments as: 

Mpg = 0.523 (— 3,280w — 283Wazp — 322Wepa) 
— 1,715w — 148Waz — 169Wea 
— 0.223 (— 3,280w — 283Wap — 322Wea) 
732w +. 63W ap 72Wea 


For load in Span 2: 

Mi, = Mt, = — 0.107wL? for uniform load 

Mio = ME, = — 0.0171 WacLi — 0.0025Wesl} = — 0.0196WecL} 
for haunch loads since Wgc = Wez, and by Eqs. 5 and 6, page 15: 


Ms=Mc=—0.107 (0.477 +0.223)wX1822—0.0196(0.477 +0.223) WaeX1822 
= — 2,480w — 455Wac 


I ll 


Mc 


For load in Span 3 by symmetry: 
Mp =732w + 63Wap+72Wea 
Me = — 1,715w — 148Wap — 169Wea 


The total dead load moments at supports may now be obtained by adding 
the moments due to loads in each span, noting that Wgc = Wea: 
Mz = Mc = — 3,463w — 85Wap — 552Wea (Eq. 12) 


*Continuous Concrete Bridges. 


20 


Step 7. Check Assumed Sections 

The thickness of top slab was determined under Step 1 and will not be 
increased unless needed to accommodate the main longitudinal reinforce- 
ment over piers. 

From Fig. 3a the weight at centerline of span can be computed as 1,690 
lb. per ft., which is the value of w used in Step 6. From Fig. 3c the weight 
at the outer ends of end spans is found to be 2,150 lb. per ft. and from Fig. 3b 
the weight at the piers is 3,220 lb. per ft. Then 

Wap = 2,150 — 1,690 = 460]b. per ft. 

Wea t5, 220) — 1,690 = 1,530 Ib. penft: 
Substituting values of w, W4z and Wg, in Eq. 12 gives for dead load moment 
Msp = Mc = — 3,463 X 1,690 — 85 & 460 — 552 & 1,530 = — 6,736 ft. kips 


Section at Centerline of Span 2 
Dead load moment 


1 1 
G X 1,690 +75 X 1,530) 1822 — 6,736 = 1,316 ft.kips 


984 ft.kips 
Total = 2,300 ft.kips 
Taking into account compression in the web (neglecting fillet) and con- 
sidering the effective depth to be 48 in., stress analysis of the section shows 
fe = 1,075 p.s.i. and fs = 17,550 p.s.i.* with twenty-eight 11,-in. square 
bars required, which indicates that the assumed section is satisfactory. 


Live load plus impact moment 


Section at Piers 


Dead load moment = — 6,736 ft.kips 
Live load plus impact moment = — 2,111 ft.kips 
Total = — 8,847 ft.kips 


Again taking into account compression in the web (neglecting fillet), 
and an effective depth of 148 in., stress analysis of the section at the piers 
shows fe = 740 p.s.i. and fs = 17,280 p.s.i.* with twenty-eight 114-in. 
square bars required. See Fig. 10 for arrangement of reinforcement. 


Fat OS. “th col 
oe" asi 


Eat a a = LI “a oom we awe: = = raf e =a =m 


ri =e ge de 
eee 


i 


- Is] —4"% spacers @15" 
/ il cals a 4 } 


\_ "spacers @ 18" 3s 
Fig. 10. Section at piers showing reinforcement. 


*These stresses are based on computed values of j, but in the determination of required 
steel areas as given in Table V the value of / was limited to 0.92 at all sections. 


Zi 


Section of Maximum Positive Moment in Span 1 


The live load moment was determined under Step 5 at three sections in 
the vicinity of 0.3321. The live load moment at those sections must be com- 
bined with the dead load moment to determine the maximum moment, and 
the assumed cross section at that point should be checked. 


Section 0.30L, 


Dead load moment 


Hose) Sh ol 
(1,600 X 65 + 460 Xz Xe 1,930 XZ x3 )0 .70X130 = 12,750 ft.kips 


_ 1,690 912 — 74 X26? 1,530 X 65 (26 465X :) 
2 ax 4 3) 
— 0.30 X 6,736,000 = —11,500 ft.kips 
1,250 ft.kips 
Live load plus impact moment = 880 ft.kips 
Total M301, = 2,130 ft.kips 
Similarly 


Total M_331, = 2,130 ft.kips 
Total M351, = 2,110 ft.kips 


Stress analysis of the section at 0.33L; having an effective depth of 51.7 in. * 
shows fe = 950 p.s.i. and fs = 17,600 p.s.i. with twenty-four 1]g-in. square 
bars required. See Fig. 11 for arrangement of reinforcement. 


ee spacers G12" %'> @5%" 
aw ESE PEE ww Bae 
ae alia 10 ae ae eae 
"> es" CH, iF ee 54> @6" 
ae oll - 
SH 
4 gn 
‘ 2 1%6 
Ho 2p %"> spacers @15" € 
at | Hh ! 


46% 


¢ 
No | 
> j * = s 
a 
1%'5@ 4" ait Le = 
Tr ey Oe o ale hse s0 ee — 
a ee ue rrr oe ee ea a ee 2 oe oa 
5 = i é 


3s ’"? spacers @18" 


a 


Fig. 11. Section at 0.331; showing reinforcement. 


It will be noticed that the sections checked could be reduced somewhat 
and still keep f; less than 1,200 p.s.i., but it is evident that the arrangement 
of a greater amount of reinforcement necessitated by the reduced section 


*Effective depth taken as 3 in. less than over-all depth. 


Z2 


may be less desirable. Moreover, before reducing any section the maximum 
shear should be checked. 

It is obvious that the maximum shear will occur at right of Support B 
when Spans 1 and 2 are loaded as shown in Fig. 12. 


WHEEL#] #2 #3 #44#5 #647 #8 #9 Hig Hy) HZ HI3 
J5P 3P ISP 3P 15P_ 4p Pp 3P 15P 3PI5P 3P 75P 


lou. CO le taal @ ite @r6 GLO _ (OL OLe Cc D 
30° Jia], 30° [ial 30° Nal 30° 1a'l 30" |1a'| 30" |1a" 


SPAN 2 SPANS3 


Fig. 12. Loading for maximum shear at right of Support B. 


For this loading 
Mp = (—0.304 X 0.75 — 0.274 X 3) P X 130 
+ (—0.035 X 1 — 0.291 X 3 — 0.277 X 0.75) P X 182 
—136.5P — 203.0P = —339.5P 


and 


Mc 


(15160 750.117 3) PX 130 
+ (—0.018 XK 1 — 0.288 & 3 — 0.292 & 0.75) P X 182 
58.4P — 200.5P = — 142.1P 


in which P = 5,360 lb. 


339.5 142.1) 5,360 
Mm eee 2.1) 5,560 + 10.56 X 5,360 = 62,400 lb. 


182 
1,530 
Dead load shear = 1,690 X 91 + —3— X 91 200,200 Ib. 


Total shear = 262,600 lb. 


I 


262,600 


Specs. eee © ome 
TOn Ve (ROSESCMIAGta cues 


U 


The unit shear exceeds 0.06 f, only slightly and it should be possible to 
arrange the shear reinforcement without difficulty even though all shear is 
taken by the steel. If additional headroom is of value, some reduction in 
depth may be made, but since the amount of all reinforcement will be 
increased, except the transverse reinforcement in the top slab, it may prove 
less economical to do so. For the purpose of this problem it will be assumed 
that the sections are satisfactory as chosen. 


Step 8. Draw Maximum Moment Curves 


In order to draw maximum moment curves it will be necessary to com- 
pute maximum positive and negative moments at several points in addition 
to those already computed. The procedure is essentially the same as for 


*See footnote page 21. 


23 


terms of Pe 


4 


M.et, in 


ere Onn Siti en tigg iets are eet 
INFLUENCE LINES FOR Mai, 


USE L OF SPAN IN WHICH LOAD JS PLACED 


Eigeml os 


those points already illustrated, so the detailed calculations will not be given. 
When computing negative moments at 0.8L; and 0.2L, it will be found 
helpful to first draw influence lines as shown in Figs. 13 and 14 since partial 
loading of the spans is necessary to produce maximum moments at these 
points. In actual practice it is of course not necessary to draw the influence 


24 


INFLUENCE LINES FOR Ma, 
pete 


Le 


SPAN 2 


USE L OF SPAN IN WHICH LOAD IS PLACED 
epee Tae 


H 
Ae 
q 


: =: 
; ote ; 
: Site i Fes : t | pea tes pee Aes sth i 
fear i ; i : ij { | sae laa as Z I t 
tease jh hs east : H : : i : cree ee 
+ =. H 4 i bs ; + : b H } es | = . H ¢ t t ; 


pn olts RAROS Seren mses Ca aTee cee 
? Pe eests 


Fig. 14. 


lines for both positive and negative moment nor for spans which will be 
fully loaded. They have been shown here simply to enable the designer to 
get a clear picture of the loading conditions. Figs. 15 to 20 show positions 
of trucks to give maximum moments at intermediate points for which dead, 
live and total load moments are given in Table III and plotted in Fig. 21. 


2D 


WHEEL 4] #8 #9 #10 #11 Hy) #2 Hx 8y 4546 
Hae A a) 20 c _GPaSP | 4? Pe eae ators 


QO Tal Tel rhe te rad 
| 30° | 14° | 30° | 14.5 | 30" | | 30" | 
age. c0 ais 65 Cot 


4 


Fig. 15. Loading for maximum positive moment at 0.6L). 


WHEEL #) #2 #3 #4 #5 4G #7 42 
3P ISP 4P P SP ISP SP ISP. 


GLis Ore Clie 
fia | 30" [ia"| 30° [14°] 


Fig. 16. Loading for maximum negative moment at 0.61). 


WHEEL#!] #2 #3 #4 #5 #6 #7 #8 Fo HO | By HZ 
3P 15P APP 3P 15P 4P Pp 3P 715P —3P 75P 
AOoQ Oo by (Olen. AOLG Oro @romc D 
Ig" i974. [ia] 30° [1a 30° [ia] 30" [14°] 


35L2 


Fig. 17. Loading for maximum negative moment at 0.8L). 


WHEEL #1 #2 #3 #4 8 #5 #6 #7 ¥— 8049 #10 
; 3P15P app 3P ISP 4P P 3P 15P 


Oa ©"0 Oot hie 
aria 30° fia] 30° [ia] oat sa 
rao Le 


C D 


Fig. 18. Loading for maximum negative moment at 0.21». 


WHEEL #1 #2 43 #4 «#5 HG 

3P ISP app 3p 15P 

Ore @ke Oem) 
his4'| a", 30° |14'] 30° [14° 


L3=130' 


Fig. 19. Loading for maximum negative moment at 0.3L». 


WHEEL #) #2 #3 44g #5 HG #7 Hg 


Fig. 20. Loading for maximum positive moment at 0.3L». 


26 


n ft. kips 


Table I1I—Maximum Moments at Sections 
Required for Drawing Moment Curves 


Dead load Live load plus Total 
Span Section moment, impact moment, moment, 

ft.kips ft.kips ft.kips 

0.00L, 0 0 0 
OBevon ANS 911 2,130 
0.60L, —227 844 617 

: 0.60L; 297 —814 —1,041 
0.80L, = P57 NO —1,210 —3,920 
1.00L; 0,0 Sel dal — 8,847 
0.00L. —6,/36 Stil — 8,847 
0.20L2 —1,338 —862 — 2,200 
2 0.30L2 170 —582 —412 
0.30L2 170 662 832 
0.50L. 1316 984 2,300 


Bending Moment i 


27 


Step 9. Draw Maximum Shear Curves 


In order to draw maximum shear curves find the shears at the supports 
and at the 0.3 or 0.4 and 0.6 points in each span. It will be noticed in 
Table IV that the shear at 0.4Z; is negative even when the live load is 
placed to give maximum positive shear, so the maximum positive shear has 


WHEEL?7 #8 #9 4190 | B12 
4p Pp 3P 15P _3P 75P 
O OWeL® 8 


Fig. 22. Loading for maximum shear at Support A. 


WHEEL #7 #8 #9 #10 #) #2 43%, #5%G 
APP 3P ISP & asp & Bs AB Ish, 
© Ox B 


Fig. 23. Loading for maximum shear at 0.3L). 


WHEEL #1 #2 #3 #4 #ote #7 #g— Ho #10) Hy Ry2 
15P.3P P 4P J5P.3P J5P_3P 
Ci@mEor® O O 


oS DES Panel 


Q© Q 
Rzo']ia'|_ 30° 14) 


.60 1, 


€ 


Fig. 24. Loading for maximum shear at 0.61). 


WHEEL #1 #2 #3 #4 #5 4G #7 HR HO HIQ Hy Hie | HyR #14 
ISP3P JI5P3P P _4P J5P3P JSP3P (oe 3P TSP 3K 
Q©O 00 OB ®) ue) 


Fig. 25. Loading for maximum shear at left of Support B. 


WHEEL #] #2 #3 #4 #5, HG #7 #— #9 #10) | Fy HZ 
3P 15P 4p P 3P 15P 4p Pp 3PI5P 3P.15P 
©) B ©) Ohio CLE 


Fig. 26. Loading for maximum shear at 0.4L;. (Note: For maximum shear at 0.6L», 
reverse truck-trains and place load in Spans 2 and 3.) 


28 


been determined at 0.3; in order to plot the curve of positive shears in that 
span as shown in Fig. 27. The position of loads for the shears tabulated are 
shown in Figs. 22 to 26. Additional shears have been computed and plotted 
thus, e, in Fig. 27 to show that the curves drawn as straight lines through 
two points near their extremities are sufficiently accurate. 


Table IV—Maximum Shears at Supports and 
Intermediate Sections Required for Drawing Shear Curves 


Dead load Live load plus 
Section shear, impact shear, 
kips kips 


Support A AAO | 43.0 
0.3L; = 4S) 2221 
0.4L, = 2Hk0 Les: 
0.6L, =i | 3007 

Support B == les 


Support B 200.2 
0.4L. Shh 
0.6L. = 

Support C —200.2 


3 


i 


~ MAXIMUM TOTAL S 


SNERREHE 


| SPAN | | 
eng ieeentes : 


wd 
{ 


| | } pet 
POSITIVE SHEARS {| aS id eg sae Ga “ NEGATIVE SHE 
EER Latent tb knee $235 -+- = reat i. pe H ; a 


fate | 


esd | py | PHENO Gale 
AIN REINFORCEMENT CUT-OFF DIAGRAM 4 a 


stent a t 


8-1/4" bars 26" 


pesos a 


+ SPAN z 
eGGe vem melee eee UE eee eae 
4-14" barsi conti ved in Span 2. 
-4s"B bars cd 

~ 


ts contin 


Fig. 28. 


Step 10. Select and Arrange Reinforcement 


From computed moments and shears given in Tables III and IV used in 
plotting the maximum moment and shear diagrams and values for inter- 
mediate points taken from Figs. 21 and 27, Table V was prepared show- 
ing required amounts of main reinforcement and stirrups. The j-values for 


64-6" 62-0" 
G56" 46:0" 
42:6" 30*+0" 
£4'@ 122 bars each 34:6" lon jet - | 
SS SS ae ee F 4 | Z| SS es 


8-1%"2125°6" long -k VW t Pca Tic ml Use aes 
@i2-Welded splices | | 


| 3-14" 196-6" long | _—_f Sa Ae aes i= ue 
f @i2*Welded splices_y 


$— 5-14" 9126" long @12" 


soa ae 
& Girder Web3 3 eee. | 4-14" 51S" long @4 


fl 

i 

| 
i 


| — | 


~t__ 26 @l2™2 bars each 31:6"long 


54"6@ 8" in bottom of slab (Longitudinal slab reinf.) a 


%"> © 5%" in top of slab and %e"$ @ 6" in bottom of slab (Transverse slab reinf.) 


Fig. 29. Arrangement of negative moment reinforcement in top slab of girder 
(8-ft. width ). 


30 


T-beams of the dimensions used vary from 0.92 to 0.95, so the smaller 
value was used in determining reinforcement for all sections. Fig. 28 shows 
number, length and sizes of bars required for main reinforcement. Figs. 29 
and 30 show the arrangement of reinforcement in plan. Fig. 31 shows size 
and spacing of stirrups and details of the stirrup arrangement. 


Table V—Maximum Moments and Shears and Required Reinforcement 


Positive] Negative] Positive} Negative} Depth of A;, sqane* ’ Shear ~~ 
Point }moment,} moment,} shears, | shears, | section, reinforcement 
ft.kips | ft.kips kips kips in. Top |Bottom| Size |Spacing 

0.00L; 0 B15 114.0 Eat nde 8257/5 |e ware 0.0 |2-5¢rd.|_ 11 
0.10Z; | 1,100 iy ogee 82.0 Ae a 71.3 so off TG Bsvsrreli| a3 
0.20L, | 1,800 Len 49.0 ay ee « OYA lla 5 ol] FAW I Zexeiell| iG 
OSE: ||, AUD po a a 17.8 6 Hee 56.1 sco ol Zen |2vArgab|) 246 
OMS Eile22 130 ee ese ee 54.7 eee P29 oe | eee ee | a ane 
0.40L, | 2,050 oe Oe: eas Be 36.CF 523 5 4 0 || CUR Pee ercl) wil 
0.50L; | 1,550 nee: Phe 220 51.0 56 4) 2oetb | oesieek| als 
0.60L, 617 1,041 Ss MOSH 55.0 14.8 8.6 | 2-34 rd. 11 
WEA Ea, Siler 2,300 Ae ade 144.0 67.2 ANGE || oo a || Dovargele 10 
OFSO La eneouss 3,920 ao 180.0 87.4 BA eee |2=s4rd: 11 
Over |} 6 5 = 6,100 Aare 216.0 ANS EI BBG fa a 6 | Bevrarel. 12 
OO Die lee cs 8,847 Sai eile 152.0 4o.4 ee a 2=e4 rd. 13 
OOS Ils 6s 8,847 262.6 aa 152.0 Wee Wa 6 6 Wwyisgely|— ale 
(OMOEA 5 oe 4,750 213.0 ey oc WS 7 ZO |] os o | ABA ral 12 
O20 773) | enna 2,200 163.0 rid Ne as 87.4 LOFTS eee 2=s4 rd.) 612 
0.30L2 832 412 112.0 ee eg OWeZ 4.7 9.4 | 2-84 rd. 13 
0.40L2 | 1,950 BOR ay: 63.2 Age 55.0 » 5 off GZ |paverel|| ae 
0.50L2 |} 2,300 : : cede es ean 


*; assumed to be 0.92 throughout. Effective depth for negative reinforcement taken as 
4 in. less than over-all depth and 3 in. less for positive reinforcement. 
**Spacing of shear reinforcement is shown to the nearest inch as computed. Actual 
spacing as used in the girders is shown in Fig. 31. 
Taken from Fig. 27 instead of Table IV. 


21-6" ec can cers ee 60*6" long 
ee 2 

ae : 

ae — 8-1'8"® 10:0" long 8-1%8"2 16-6" long— 
| u @ 12" @12" 


| ——— ee 8-149 86'G6" long 8-14"9 89-0"long—= —t— 


™ 

< 

oF Tee ee = 

& PEP e nn ee a | ee — 
ie) = 
= 
w 

# 


pet a Ee ann eo 2» 1 
—_——_—_ i ss ee Se o 

ry ig 4-14'5 33-O"long ———— asd 

' ——— me, 
SSS Se atl is 
=e ae ee ineseta [rete aol fa) Pale 


=== ee al 


ye %"0 @12"-3 bars each 32-0" long 


ei "> @ 18"in bottom of slab, transverse 


Fig. 30. Arrangement of positive moment reinforcement in bottom slab of girder 
(8-ft. width ). 


31 


"See detail BY ‘ Pe Corciwen ’ 
3:8" 54’ Bspaces jemre (58? 9spaces %4'973 spaces @10"= GO-10 & 


@15"=7-6" | @10"=1-6" 
Pier at B 
ae 


€ Pier B . ; < e +e 
%4'd inclined stirrups in pairs S¢spaces @12"+52:0" 56° 25 spaces @10"=20° 10" SgoSspaces _%" G spaces _ III 


End A 

B(% inclined stirrupsin pairs; %8spaces ak 56% © spaces 
| 18 spaces @ll"= 6-6" @15% 10:0" [ @20% 100" 
| | 


@ 20"= 13-4" 


Span _1-130:0" | 


++ 


Half of Span 2 - 91-0" 
SIZE AND SPACING OF STIRRUPS- SYMMETRICAL ABOUT € SPAN 2 


(8) seep stirrups in pairs @1\" 


Note: 

All stirrups in pairs 
All stirrups are in- 
clined except at ends 

of bridge AGD 


ely ede 


ge? stirrups | 
‘in pairs staggered 
9spaces@ 7's" 


> b Se aa 

aye ON ROSE Hooks on top to 
GE N& Se asection in Span2+ 
Vx QQdn< 8! frot pier 


- A 
+ Hooks on top to 4“ 7 


Weld or make 
{ 40 dia.lap 
DETAIL OF : 
STIRRUP 


G" | 
DETAIL AT Piers 


Fig. 31. Arrangement of shear reinforcement. 


Step 11. Compute Deflections 

Dead load deflections are computed in Table VI at each tenth point of 
each span. Fig. 32 shows the deflection curve, deflections being plotted in 
feet. It should be noted that a negative deflection indicates a rise above the 
final desired grade and a positive deflection signifies a sag below the desired 
grade for which compensation should be made in construction. 


7 | DEAD LOAD DEFLECT 
=O.) Fee ees i pe : edie se iega ics fang ' oe es 


meky (bape Fu eee 


Shae 


,Deflection,in feet 


32 


Table VI—Dead Load Deflections 


Uniform Haunch, Total 
deflection 


39.02 5 8:49 
(Ses |e 
MO |) = Zeke 
NIOLS). || =Ash,8)7/ 
1390S -50526 


*For Span 2, effect of Mg = Mz is included. 


w = 1,690 lb. Walt _ A 
Wa = 460 lb. EIo 

We = 1,530 lb. Welt _ ee 
Mp = Mc = —6,736 ft.kips El¢ 

Eo = 1.5 X 10°p.s.i. WeLs apa 
Ie = 683,200 in.4 EI¢ 

wy MsL? | 

EI, 7 0-471 Erp 7 O11 
why MsL2 _ 

i aes ea Bi = 0-217 


33 


Section V— Details 
Diaphragms 


The number and size of diaphragms should be limited to the minimum 
required for structural safety because they not only add weight, making it 
necessary to increase the capacity of the structure, but they materially 
increase construction difficulties. 

It is not possible to determine mathematically where diaphragms should 
be located nor the dimensions of them. Obviously the thinner the members 
of a hollow girder in proportion to their unsupported span the greater the 
need for contributing stiffness through diaphragms. It is recommended that 
in bridges having interior spans not greater than 200 ft., diaphragms should 
be located over the supports and at the quarter, half, and three-quarter 
points. For longer spans the spacing may be limited to 50 ft. 

Over supports and in negative moment zones it is advisable to provide 
a diaphragm at top and bottom. In positive moment zones, diaphragms at 
the top only will be required. The diaphragms should be 10 to 12 in. thick 
over supports and 6 to 8 in. thick elsewhere and should be about one-third 
of the height of the girder at the section where they are located. This will 
leave sufficient space for easy removal of inside forms. A small amount of 
reinforcement should be provided, say 0.25 to 0.30 per cent. This amount 
of steel should be distributed throughout the depth of the diaphragm. 
Diaphragms for the bridge of the preceding design problem are shown in 
Fig-)33: 


Expansion Bearings 


Conservative allowable working stresses should be used in the design of 
bearings for hollow girder bridges since the large reactions encountered are 
mainly due to dead load. It is thought that a value of 600d should be used 
for bridges of the type considered here. With an edge distance of 3 in. on 
each side of the top bearing plate, 1,000 p.s.i. bearing for a 3,000-p.s.i. 
concrete will be sufficiently conservative. ‘The bottom bearing plate should 
be made the same size as the top plate except that it must be extended 
either in length or width sufficiently to receive %4 in. to 1-in. diameter 
anchor bolts. 

To design the bearing at the interior piers of the foregoing problem 
assume that the Bureau of Public Roads standard 1134-in. radius, wide- 
flange beam rocker will be used. The maximum reaction to be carried will 
be obtained when the wheel loads are in the position for maximum shear 
to the right of Support B as shown in Fig. 12, and the reaction will be: 


Live load plus impact from Span 1 = 35.0 

“ “ “ “ “ Span Y — 62.4 

Dead load from Span 1 = 191.8 

e =) eseeopaniie = 200.2 
Rg = 489.4 kips 


34 


(a) BEARING AND DIAPHRAGMS AT Free End 


Back wall to be built after 
deck forms have been removed 


%" bituminous joint at all 
intermediate diaphragms 


omit bottom diaphragm 
at 4 and % point of end 
spans and at center of 
interior span 


(b) DIAPHRAGMS AT INTERMEDIATE QUARTER POINTS 


12'\12'-65* H-section split on€ 
\"Premolded mastic \ a x 
1% welded 


~ Approach’. k > : , 
ia slab [y: of - KON y ~ ® Reinf. rod 18"long 


welded @/8"ctrs 


(Cc) EXPANSION JOINT 
ea ABUTMENTS 


2" drain 

: ¢ each cell 
~02"(10% cy 

F Ti empera ure yn 

when constructed é Lead plate 
(d) BEARING AND 

DIAPHRAGMS AT PIERS 


Fig. 33. Diaphragms and expansion joints. 


oP) 


Allowable load == G00) Xt 5e x2 = 14,100 Ib. per in. 
Length ired = ponies = 34.71 36 1 

ength required = 14,100 = 34.7 in., use 36 in. 
a see ges 489,400 a aque 

rea require = 1,000 = sq.in. 

490 : ; 
Width of plate = 36 = 13.6 in., use 14 in. 


1,000 X 72 X 0.5 
Thickness = a 


18,000 -—— = 2.86 In. Uses 


The procedure for designing the end bearing will be the same as for an 
interior pier. If a rocker of the same diameter is used at the end as was used 
at the interior pier, which is advisable, a length of only 8 in. would suffice, 
but for practical consideration a 12-in. long rocker will be used. Fig. 34 
shows a cross section of the bearings at piers and abutments. 


¥" Webs 
@G6'c.c: 


K-I'2"plus width required\_yu, 
for anchor bolts Ny Lead plate eA 


ENO VIEW SIDE VIEW 


Fig. 34. Rocker bearing detail. 


Section VI — Substructure 


Piers for hollow girder bridges may be made either hollow or solid. At 
the fixed bearing of a continuous deck bridge it is advisable to use a hollow 
pier so that width for stability may be obtained economically. When the 
deck is made integral with all the interior piers, unless very high, it is better 
to use a narrower solid pier to avoid a large pier stiffness. Very stiff integral 
piers of long-span bridges are subjected to large moments due to temperature 


36 


changes, which in addition to those of unbalanced live loads, may make the 
use of a stiff pier impractical. 

The hollow pier is gradually coming into general use. Its chief value is 
to reduce quantities where a wide bearing plate requires a wide pier cap 
and consequently a wide or thick pier. Another use of the wide hollow pier 
is to provide architectural balance; a narrow solid pier may appear too 
slender for the span it supports, even though it is more than adequate for 
all the forces to which it is subjected. 

The thickness of the outside walls of a hollow pier should not be less 
than one-tenth the unsupported height between horizontal diaphragms 
which should be about 10 or 12 ft. apart. The outside walls must be thick 
enough and sufficiently reinforced to withstand the impact of drift and ice 
pressure, if so subjected. A vertical diaphragm should be provided under 
each bearing. These walls should be about one-twelfth the unsupported 
height and the horizontal diaphragm may be made about the same thickness 
for easy construction and stability. Hatch holes should be provided in the 
horizontal diaphragm to facilitate removal of formwork. 

Open abutments have numerous advantages and will not be subjected 
to large overturning moments if the backfill is placed in thin layers and is 
compacted thoroughly before the superstructure is placed*. The width of 
base need not be more than 0.25 H to 0.3 H where H is the height from 
bottom of footing to bottom of roadway slab. Thickness of counterfort walls 
may be 18 to 24 in. depending upon height, spacing and load carried. 


Section VII — Forms and Falsework 


It appears impractical to erect falsework for a continuous hollow bridge 
unit in two or more stages; complete falsework for a whole unit should be 
erected at one time unless it can be founded on solid rock and extreme care 
is given to wedging. Falsework for a large hollow girder bridge should be 
founded on driven piles if possible. Mud sills should be used only when the 
driving of piles is not feasible. 

Hardwood wedges should be provided in such quantity and quality that 
adjustment to original elevation after each placing operation can be made. 

In general, the forms for a hollow girder bridge do not differ materially 
from the forms for any other type bridge. There are, however, a few details 
in connection with the inside forms which may well be discussed. . 

Forms for fillets between bottom slab and girder web should be built 
so that the concrete for the bottom slab and fillets can be placed in the 
same operation. Fig. 35 shows a type of form arrangement enabling the 
placing of bottom fillets with bottom slab. The bolts may be provided with 
sleeves of proper length to gage the slab thickness, or bolts with removable 
heads may be used and the thickness of slab established by other means. If 
sleeves are used, it will be necessary to detail them to exact thickness of slab 
which varies from point to point. When bottom forms are removed the bolts 


*Continuous Concrete Bridges, page 97. 


ai, 


of each frame — 


2x4" across top Sa Stirrup dowels 


Fig. 35. Suggested detail for inside forms. 


holding the fillet can be removed and replaced, leaving in blocking and 
fillet forms (Fg. 35a). 

As shown in Fig. 35b the forms for vertical walls and top slab can be 
built so that they are easily removable. When the side form of Cell 1 is in 
place, the reinforcement in the web is placed and then formwork for Cell 2 
is erected and so on across the deck. 

Before concreting the top slab, all or practically all these interior side 
forms may be removed if diaphragms are built as shown in Fig. 33, leaving 
sufficient room for form removal. The above arrangement of forms allows 
the removal of slab forms in full-width units after removal of side forms. 


PI ZZLLLLLRL. Zs 


(F7IZZZ) \st Operation ase we ‘s 


INNANN] 279 Operation 
CLLITTTT) 34 operation 
ROO 4th Operation 
EE 5*¥ Operation 


SECTION A-A 


Fig. 36. Concrete placement schedule. Order of placement indicated by opera.on 
numbers is symmetrical about centerline of Span 2. 


38 


Section VIII —Suggested Concrete Placement Schedule 


Operation 1—Place bottom slab continuously from End A to End D, Fig. 36. 
Operation 2—Before beginning this operation, wedge forms up to original 
elevations. Place web walls and diaphragms over piers. 

Operation 3—Wedge up forms again to original elevations, and place webs 
and diaphragms between points of contraflexure (£, /) as shown. 
Operation 4—Wedge up forms again to original elevations and place top slab 

between points of contraflexure as shown. 
Operation 5—Final operation, place top slab over piers. 

The unit composed of bottom slab and fillets, as placed in Operation 1, 
is very flexible, and yet it provides an appreciable amount of weight so that 
the major settlement of falsework takes place under this loading. Wedging 
the forms back to original elevation wil] stress the slab only an insignificant 
amount. Placing sections marked (2) next makes it possible to place the 
construction joint in webs on a 45-deg. slope, parallel to the inclined stirrups, 
which is parallel to the plane of maximum diagonal compression, and per- 
pendicular to the plane of maximum diagonal tension. In this way there 
will be a minimum of interference of reinforcement in making the joint; no 
stirrups outside of placement Operation 2 need be placed beforehand. 
Cracks would not be expected along this plane since theoretically only 
compression stresses can be present. 


Section LX — Curing and Removal of Forms 


No falsework should be removed until 15 to 20 days after completion of 
the top slab, but in no case until concrete in placement Operation 5 has 
attained a compressive strength of 2,500 p.s.i. as determined by test cylinders 
cured under conditions similar to that of the slab. The moist curing period 
should not be less than 5 days after placement of concrete except that for 
high early strength concrete moist curing should be provided for at least 
2 days. All construction joints, such as top of fillets of bottom slab and top 
of vertical walls, should be properly prepared to secure the best possible 
bond between the old and new concrete*. If proper care is taken in bonding 
new concrete to old no extra precaution such as providing keys will be 
necessary. Shear at the junction of fillet and stem may appear high, but 
since this is pure shear, shearing stresses less than 0.2 f’, are not dangerous, 
except as they contribute to diagonal tension stresses. Diagonal tension is 
taken care of by the inclined stirrups. 

Removal of falsework should begin at or near the centerline of the unit 
and proceed each way to the free ends. The removal should be carried out 
carefully so as to prevent any sudden application of dead load but should 
be completed in one continuous operation if possible. 

Falsework and platforms for placing the various sections should be inde- 
pendent and free from the falsework of the bridge proper in order to preclude 
loosening wedges and distortion of formwork. 


*“Bonding New Concrete to Old at Horizontal Construction Joints” by R. E. and 
H. E. Davis. Journal of American Concrete Institute. May-June 1934, page 422; also Bonding 
Concrete or Plaster to Concrete published by Portland Cement Association and available 
free on request in U. S. and Canada. 


29 


CONCRETE 
BRIDGE 
DETAILS 


¢ 


aes : 
ORTLAND CEMENT ASSOCI 
con ee : ss | 


CONCRETE BRIDGE 
DETAILS 


CEMENT ASSOCIATION 


PORTLAND 


The activities of the Portland 
Cement Association, a national 
organization, are limited to 
scientific research, the develop- 
ment of new or improved prod- 
ucts and methods, technical 
service, promotion and educa- 
tional effort (including safety 
work), and are primarily designed 
to improve and extend the uses of 
portland cement and concrete. 
The manifold program of the 
Association and its varied serv- 
ices to cement users are made 
possible by the financial support 
of over 70 member companies in 
the United States and Canada, 
engaged in the manufacture and 
sale of a very large proportion 
of all portland cement used in 
these two countries. A current 
list of member companies will be 
furnished on request. 


GEOFNaieE Noes 


Introduction 
Abutments 
Abutment Footings . 
Breastwalls 
Wingwalls 
Bridge Seats . 
Abutment Movements 
Joints 
Joints in Abutments 
Joints in Decks 
Drainage 
Wearing Surface 
Handrailings 
Creep in Skew Bridges 


Approach Settlement 


ee) tery fe i 


11 
17 
21 
22 
24 
26 
32 
34 
36 
41 
46 


TO OUR FRIENDS 
IN ENGINEERING 


A CLEAR distinction between good and bad is sel- 
dom justifiable in the study of technical subjects. In 
bridge building, for example, bad practice does not exist— 
in a sense—since it has to a great extent been discredited 
and discarded. It seems equally true that good practice— 
in the sense of perfection—has not yet been achieved. 
Bridge building is still in an intermediate stage on the 
road of progress. It is expedient at times to look back 
and survey past stages for the purpose of outlining the 
future course. This is the viewpoint taken in the prepara- 
tion of this booklet. 

No published records were known to deal with practice 
in bridge construction as it is treated here. Hence, it has 
been deemed wise to let the discussion go beyond the 
known present practice. Care has been taken to avoid 
presenting ideas as new, for what may appear new might 
possibly have been used previously. The plan has been 
not to pass judgment but to present a discussion based 
upon field observations. It has been the purpose to offer 
constructive suggestions hoping to accelerate progress. 

The figures and marginal notations are arranged to 
give an outline of the topics treated and will therefore give 
a good idea of the scope of the studies. The text is 
grouped around the corresponding figures and may be 
referred to as the need arises for studying individual 
subjects. 


Portland Cement Association 


CONCRETE BRIDGES 


A discussion of 


structural details 


INTRODUCTION 


CoNCRETE occupies a prominent position as a bridge build- 
ing material. Beauty and economy, low maintenance cost and long 
life are among its advantages. By modern methods of proportion- 
ing, concrete is being made with a density to withstand severe 
outdoor exposures, and predetermined strengths can be obtained 
consistently. Recognition of the improvements in concrete making 
is gradually being given by increasing the working stresses. Corre- 
sponding developments have taken place in the application of 
principles of continuity to bridge design. 

Successful designs in concrete, as in other building materials, are 
frequently marred by isolated imperfection of detail. In order to 
ascertain the structural shortcomings and learn how to avoid them, 
a survey of concrete bridges was made. This survey, during which 
attention was focused on the details needing improvement, was 
augmented by information obtained through the cooperation of 
several state highway bridge officials. 

Practically no signs of distress were observed in the structural 
elements—slab and girders—which form the usual deck girder 
construction. Cracks were seen in only very few instances, and 
these were insignificant. 

While deck girders were seen to be virtually without defects, 
some abutments revealed signs of structural flaws. It became 
evident as the survey progressed that most of the defects were of 
structural nature. The types of cracks observed were evidence of 
tensile strains that could either be taken care of or be eliminated. 
Where this was not done, secondary effects were sometimes in 
evidence, such as leakage accompanied by local damage. 

The observations indicated that abutments in general do not 
actually behave according to assumptions. The conventional 
analysis of the common type of abutment is at best only an approxi- 
mation and frequently is considerably in error. 

Some progress has been made by simply strengthening the abut- 


5 


General Con- 
siderations 


Movements 
of Footings 


ment without changing the conventional type of layout. Remedies 
of this kind are of necessity empirical. It is preferable in some cases 
to develop new improved types that are subject to a more rational 
analysis in order to satisfy the modern demands for permanence and 
economy. In the development of new types—and in the general 
improvement of structural details for bridges—lies a possibility of 
greater progress. 


ABUTMENTS 


Bridge abutments perform a double function; they carry the 
load from the superstructure down to the foundation and also act 
as retaining walls confining the embankment fill. The problem of 
developing suitable details for this two-fold function is complicated 
by the fact that most elements in abutment design are not suscep- 
tible to a rational analysis of stresses. This has prompted bridge 
designers to experiment continually with new abutment types. 
Considerable progress has been made of late and meritorious de- 
signs have been worked out. 

The sections that follow present a discussion of what is believed 
to be the most advanced practice in abutment construction in its 
present stage. The manifestations of strain within the abutment 
itself are treated in the sections on Footings, Breastwalls and Wing- 
walls, which include also studies of construction details that have 
been found to give excellent results, together with suggested details 
that may cause further advance in the construction of abutments. 
The phenomena that are contributing or original causes of the 
strains have been taken up principally in the sections on Abutment 
Movements and Creep in Skew Bridges. 


ABUTMENT FOOTINGS 


It is not safe to assume that footings are immovable in cases 
where they are built on foundations other than rock or well cemented 
strata. Footings may move horizontally as well as settle vertically 
and the movements may be non-uniform. Horizontal movements 
may take place as the result of pressure of backfill or irregular 
foundation conditions. 


FIG. 1 


It is often possible to excavate the trench for the footing without 
bracing the soil. In this case it is customary to fill the entire 
width of the footing trench with concrete. Similarly, the entire 


6 


width of the trench may 
be concreted in one opera- 
tion if the construction of 
a cofferdam is required, 
provided the sheet piling 
is to be left in place. In 
other instances, the sheet 
piling may be withdrawn 
while a concrete backfill as FIG. 1 Horizontal movement of the footing is 
shown in Fig. 1* is being checked when the concrete fills the full width of 
: : the footing trench. 

placed. A construction in 

which the footing concrete is tightly wedged between two vertical 
planes of virgin soil appears to have considerable merit. 


de Breastwall 


Footing 


rt Oaks Cals 


2a a BOS A928 ge 3.05: Bi 9 583-0) OO 


Back Fill consisting of concrete 


FIGs 2 


In connection with rigid or continuous frames, it is sometimes 
expedient to build the construction joint at the top of the footing so 
that no moment can be transmitted across the joint. The use of 
joints of the hinged types shown in Fig. 2 has the advantage of 
making the foundation pressure approximately uniform and may 
therefore simplify the design of the footing as well as the analysis of 
the frame. Similar joints with a cylindrical recess in the footing 
designed for hinge action have also been used in rigid frame bridges. 
The centerline of the cylinder must be above the top of the footing 
in order to permit unrestricted rocking in the joint. 


, 


Breastwal/ 
Breastwal/ 


X 

N a Bn 
cad aa 
Ss FP Fa 


-——+— 3 


w 


FIG. 2 Construction joints with hinge action at top of footings. Type a has a better 
hinge action, but type b has a better shear connection. 


FIG. 3 


Rectangular footings tend to settle most near the center. The 
tendency is even more pronounced in abutment footings that are 


*Note that this as well as the following sketches are not necessarily drawn to scale. 


7 


Hinged 
Footings for 
Rigid Frames 


Reinforcing 
Footing 

to Prevent 
Cracks 


Breastwall 
Types 


built continuously under both breastwalls and wingwalls, because 
the load intensity usually is greater under the breastwall. Cracks 
of the type marked d, which are comparatively rare, are caused by 
sagging. The development of crack d (Fig. 3) should be considered, 
and it is advisable to use a comparatively large amount of reinforce- 
ment placed continuously at the bottom of the footing, as indicated 
by bars d in Fig. 4. 


BREASTWALLS 


Three types of breastwall are commonly used: namely, the 
gravity wall of plain concrete, the cantilever wall of reinforced 
concrete, and the type of wall that acts as a vertical beam supported 


5 Crack in wingwall 


FIG. 3 Typical cracks that may develop in the common abutment type when the 
conventional analytical methods take little or no account of the actual behavior of 
the abutment. 


horizontally by the deck and by the foundation. There are also 
several modified types such as the semi-gravity and the buttressed 
retaining wall. 

The cantilever retaining wall, probably the type most commonly 
used for breastwalls, sometimes develops cracks similar to @ in 
Fig. 3. Such cracks may be prevented as will be seen after a brief 
discussion of their contributing causes, among which are: (a) non- 
uniform shrinkage, (b) a discrepancy between design assumptions 
and actual behavior, and (c) the earth pressure on wingwalls. The 
relative effects of these phenomena are uncertain, but all of them 
act to create tension in the front face of the breastwall. 

Shrinkage in abutment walls may be non-uniform because the 
front surface, being exposed, dries out in relation to the rear surface 
that is kept moist by the adjacent fill. This shrinkage tends to set 
up tensile stresses in the breastwall. 

In studying the discrepancy between design assumption and 
actual behavior, consider an abutment of the type shown diagram- 
matically in Fig. 3. The breastwall is assumed in the design to be a 
cantilever retaining wall and is reinforced accordingly; that is, the 
reinforcement is placed near the rear face. In reality, the wall acts 


Plan 


FIG. 4 Common abutment type, reinforced and strengthened. The ordinary abutment 
reinforcement is not shown. 


Causes of 
Tension in 
Breastwalls 


Design Dis- 
crepancies 


Bars in 
Front Face 


Joint Action 
with 
Wingwalls 


partly as a simple vertical cantilever, and partly as a box retaining 
wall braced at the ends by the wingwalls acting as counterforts. 
Wall slabs of this type have tensile stresses in the front face midway 
between the counterforts and should be reinforced accordingly with 
horizontal bars near the front face. Unfortunately, all the reinforce- 
ment in ordinary breastwalls is placed near the rear face; but the 
horizontal bars would be more effective if placed near the front face. 

The wingwalls in Fig. 3 are also designed and built as cantilever 
retaining walls but are cast integrally with ‘the breastwall, with 
two results: the whole abutment acts as a unit, and the earth 
pressure on flared and parallel wingwalls produces tension in the 
breastwall. 


FIG. 4 


According to this discussion, an abutment of the type shown 
in Fig. 3 can be improved by adding horizontal bars near the front 
face. Bars ain Fig. 4 provide for both horizontal beam action and 
shrinkage, and are recommended for use with the regular reinforce- 
ment provided for cantilever action. In addition, it is sometimes 
advisable to place vertical bars near the front face. These bars will 
take the tensile stresses developed in case the breastwall acts as a 
vertical beam supported horizontally by the deck and by the founda- 
tion, a loading condition that will be discussed in the section on 
Abutment Movements. 

The joint action between breastwall and wingwalls is difficult 
to analyze, and the safe and economical amount of reinforcement 
can seldom be calculated. If the bar areas provided happen to be 
inadequate, small cracks may aay 
still develop. As a further pre- Seay 
caution, vertical grooves should ae 
be used on the front face of 
breastwalls. The grooves are 
sometimes placed in combination 
with vertical construction joints, 
in which case the reinforcement 
should be continuous across the 
joint. The small crack will 
then be inconspicuous because it 
will follow the bottom of the 
groove, and membrane water- 
proofing applied at the joint on 
the rear face will prevent seep- ; 
age. The best result is obtained FIG. 5 Weep holes with proper stone 


packing are important in making abut- 
when weep holes are placed at ments durable. a 


10 


the vertical construction joints. At least one state highway depart- 
ment follows this practice with good results. 


FIG. 5 


All box-type abutments should have provision for drainage of 
the backfill. This involves drain pipes acting as weep holes placed 
in the walls as indicated in Fig. 5. The openings should be large, 
say 6 inches in diameter, especially where there is danger of clogging 
with dirt or ice. 

The backfill should be selected with care since it greatly affects 
the safety and durability of abutments. The fitness of a backfill 
material is principally judged by its behavior when it absorbs and 
releases water. Silt and loam, for example, have objectionable 
characteristics and may, when wet, exert pressures considerably in 
excess of those for which the abutments were designed. Coarse 
materials are better suited for backfill behind abutments because 
they quickly release entrapped water and therefore exert a minimum 
pressure on the confining walls. Coarse material may be costly to 
use for the entire backfill. If so, it is often used in a layer only, 
about 12 inches thick, placed against the rear abutment surface. 


WINGWALLS 


The wingwalls are usually of the same type as the breastwall but 
differ from it in that they are topped by a simple coping without 
provision for support of any superstructures. They will be referred 
to as parallel, flared, curved, or straight wingwalls. 


FIG. 6 


Cracks that may develop in wingwalls and at the junction of 
wingwall and breastwall are designated as b and c in Fig. 6a and in 


FIG. 6 Cracks b and ¢ in abutment with wingwalls as illustrated in left-hand sketch 
may be avoided if the wingwalls are separated from the breastwall by expansion 
joints. Two types of joint layout are indicated. 


1] 


Drainage of 


Backfill 


Stresses along 
Coping 


Improved 
Wingwall 
Design 


Fig. 3 (page 8). What is the cause of these cracks and how may 
they be prevented? 

An abutment of the type shown in Fig. 6a may behave partly 
as a box retaining wall in which the wingwalls act as counterforts. 
Tensile stresses are developed accordingly along the coping of the 
wingwall, but adequate reinforcement is seldom provided. The 
development of cracks of type 6 may therefore be a result of the 
discrepancy between assumption and reality in abutment action. 
Additional tensile strains are created since flared or parallel wing- 
walls have a tendency to pull away from the breastwall. Because 
this tendency is rarely considered in the design, cracks of type c may 
develop as sketched in Figs. 3 and 6a. 


FIG. 7 


Fig. 7 illustrates crack- 
ing that may occur in wing- 
walls built in direct exten- 
sion of the breastwall. Such 
cracks are sometimes ob- 
served where the abutting 
surfaces in the vertical 
joint between the wingwall 
and the outer girder have 
not been kept apart with a 
soft filler. In such cases, 
relative movement of the 
abutment with respect to 
the deck—tilting of the FIG. 7 The cracks in this type of abutment may 
abutment or lateral creepof be avoided by use of a construction joint as 
the deck—may be harmful. _ indicated. 

Two conclusions may be 
drawn from the observations made: (a) tensile stresses of consider- 
able magnitude may be set up in the concrete by phenomena fre- 
quently originating outside the structure, and (b) no structural 
analysis is available by which the stresses may be determined. 

Accordingly, there appear to be only two methods whereby 
improvements may be made: (a) suitable reinforcement may be 
provided—by judgment or empirical rules—in the conventional 
type of abutments, or (b) improved abutment layouts may be 
adopted in which the critical strains are eliminated. 

Using the first method, wingwall cracks of type } in Fig. 3 may 
be eliminated by adding sufficient reinforcement as indicated by 
bars marked 0 in Fig. 4. 

Cracks like c at the end of the bridge seat shown in Fig. 3 can 


12 


also be avoided; the methods indicated in Fig. 4 have been used 
with good results for relatively shallow abutments with heights up 
to about 15 feet. The deck and wingwall are separated by a soft 
joint filler at least 34 inch thick. The junction between wingwall 
and breastwall is strengthened by means of a concrete fillet which is 
reinforced with bars marked c. It is advisable to use several c-bars 
in the plane just below the bridge seat. The proportions of the 
filler and the amount of reinforcement must be based upon judg- 
ment. Such methods of reinforcing the conventional abutment often 
have been found effective. 

An example of an improved design adopted to eliminate critical 
strains is illustrated in Fig. 6a, in which the double dotted line 
indicates a vertical expansion joint. The tensile strains responsible 
for cracks are then eliminated and the wingwall acts as a simple 
retaining wall and not simultaneously as a counterfort. It is evident 
that a lateral pressure of the deck against the top of the wingwall 
will merely widen the space in the expansion joint, and critical 
tensile strains are eliminated where crack c might otherwise develop. 
A similar effect is obtained 
in the construction sketched in 
Fig. 60. 


FIG. 8 


A type of vertical expansion 
joint recently used in abutments 
is illustrated in Fig. 8. It was 
found to eliminate cracks at the 
wingwall coping but not at the 
end of the bridge seat and was 
therefore abandoned. Cracks 
at both places may be eliminated 
with the joint position in Fig. 8, 
provided the bridge seat is con- 
structed as sketched in Fig. 60, 
or the joint may be moved to 
the position shown in Fig. 6a. 


FIG. 9 


Vertical expansion joints 
placed at the end of the bridge 


FIG. 8 A vertical expansion joint sepa- 


é ee : rates wingwall from breastwall. This is a 
seats in most rigid frame bridges desirable feature provided the joint is 


(see arrow, Fig. 9) have been placed at the end of the bridge seat as 
successful. The separation of an extension of the joint shown there. 


13 


Additional 
Reinforcing 
in Conven- 
tional 
Wingwalls 


Vertical 
Expansion 
Joints 


Horizontal 
Construction 
Joints 


AAAAAA 
Aarahhbhad AAAAAMPOM 
AAnbabhabs AAASAAAAAA i ' 


FIG. 9 In rigid frame bridges, wingwalls are generally separated from the breastwall 
by expansion joints. (See arrow.) 


wingwall from breastwall is desirable because wingwalls built 
integrally with the breastwall interfere with rigid frame action. 

There is reason to believe that in both simply supported and 
rigid frame spans, complete separation of wingwalls from breastwall 
will be successful. Best results are to be expected with the vertical 
joint as in Fig. 6a and a joint type similar to that in Fig. 24 (page 25). 
It is advisable to arrange an offset as indicated at the joint in Fig. 9 
to conceal possible relative movements at the joint. The joint 
position in Fig. 6b seems less advantageous but if used should be 
combined with a joint type as in Fig. 25 (page 26). 


FIGS. 10 and 11 


Cracks at the ends of the bridge seat may be avoided by placing 
a joint vertically as shown in Figs. 6a and 9. In Figs. 10 and 11, how- 
ever, a horizontal joint is made level with the bridge seat. The abut- 
ment is first constructed up to a level flush with the bridge seat; 
then the deck concrete is cast; and finally the fillet wall (Fig. 10) or 
parapet and fillet walls (Fig. 11) are cast. This joint layout has 
been used successfully by at least one state highway department. 
It provides an offset at the joint and dowels extending across it. 
It is also advisable to place a strip of membrane waterproofing 
behind the joint, to provide horizontal reinforcement below the 


14 


FIGS. 10-11 Constructions used to eliminate cracking in abutment at end of bridge 
seat. The abutment proper stops level with the bridge seat. Parapet and fillet walls 
are cast after the deck is placed. 


level of the bridge seat, and to place a soft joint filler in the vertical 
joint between fillet wall and deck. The relative movements of the 
deck will not seriously affect the abutment proper. The only dam- 
age that may be done under unfavorable conditions will be confined 
to the fillet or parapet walls and will be insignificant. 

The use of a horizontal construction joint is also illustrated by 
the dotted lines in Fig. 7. In this case, the cracks would undoubtedly 
have followed the horizontal joint and little or no damage would have 
been done. 


FIG 2 


Fig. 12 shows a straight wingwall abutment embodying interest-. 


ing features. This layout facilitates future widening, an important 
consideration in modern bridge building. The wingwall is a direct 
extension of the breastwall and the copings are stepped-off to form 
a good surface for future extension. Where there is danger of ero- 
sion, a small return wall is often built at the end. Wingwalls as illus- 
trated here are built with a construction joint at the level of the 
bridge seat, similar to the construction shown in Figs. 10 and 11. 
The bridge seat in Fig. 12 is stepped-off to maintain a constant 
girder depth under a crowned or superelevated roadway. (See also 
Fig. 51.) 


15 


Example of 
Wingwall 
Design 


FIG. 13 


An abutment of this type recently built by the Ohio State High- 
way Department is shown in Fig. 13. It features the use of hori- 
zontal grooves—rustication—on part of the front face. Rustication 
conceals construction joints and enhances the general appearance. 


Cast after bridge 
deck I's constructed 


FIG. 12 Abutment design used by Ohio State Highway Department embodies 
these advantages: 

Straight wingwalls can be widened with little waste. 

Stepped-off coping facilitates connection with future extension. 

Return wall prevents erosion of fill behind abutment. 

Rustication conceals construction joints. 

Stepped-off bridge seat makes girders identical in depth. (See also Fig. 51.) 


16 


FIG. 13 Rustication on abutment having straight wingwalls with stepped coping. 
The fourth groove from the top conceals a construction joint. The concrete above was 
cast after the deck was placed. 


BRIDGE SEATS 


The tops of the breastwall—the bridge seats—are built to trans- 
mit either vertical loads, or horizontal as well as vertical loads, or 
these two types of load together with bending moments. They are 
referred to, accordingly, as having expansion bearings, fixed bear- 
ings, or rigid corner connections. 


FIG. 14 


A study of the effect of bearing types upon abutment layouts for 
single span concrete bridges is presented diagrammatically in Fig. 14. 
The customary arrangement shown by a in Fig. 14 has one fixed and 


E b ¢ 
Simply supported deck Simply supported deck Rigid connection 
with expansion bearing, without expansion bearing, between 
cantilever abutments vertical- beam abutments deck and abutments 


FIG. 14 Diagrams illustrating three types of layout applicable to single span bridges. 


17 


Typical 
Seat—Rigid 
Frame 


Fixed 
Bearings at 
Both Ends of 
Deck Girders 


one expansion bearing. The abutments are assumed to act as canti- 
levers, but this assumption is frequently unjustified and considerably 
in error. Many bridges built according to a behave as shown in 3, in 
which the deck has two fixed bearings. Abutments, therefore, may 
act as vertical beams supported horizontally by the deck and by the 
foundation, and should be so designed. Layout c shows a modifica- 
tion of b, in which the corners have been made rigid. In comparison 
with the conventional layout, a, the second type often is more satis- 
factory in service and may even be lower in first cost. 


FIG. 15 Fi 


The rigid connection between 
deck and abutment shown in 
Fig. 15 is typical for rigid frame P 
bridges. It consists of reinforced . 
concrete designed for shears and 
bending moment as determined 
by the analysis. Longitudinal 
reinforcement only is indicated 
here. Sufficient transverse rein- 
forcement must be added to pro- 
vide for shrinkage, torsion and 
unequal settlement. 


Construction 
Jol n 


FIG. 16 


A. Construction 


The Wisconsin Highway join 


Commission has had _ success 
with the fixed bearing detail 
shown in Fig. 16 which has been 
used for years at both ends of 
concrete girder bridges with span 


lengths up to 45 feet. The abut- 
ment is cast up to a simple con- 
struction joint as indicated at the 
top of the abutment, and dowel 


FIG. 15 Typical connection between 
deck and abutment in a rigid frame 


bridge. Main reinforcement only is 
shown. Transverse reinforcement also 
essential. 


bars are extended above the 

joint. The end of the deck is then cast directly on top of the con- 
crete in the construction joint. The dowels are not designed or 
located to resist any bending. A horizontal strip of membrane 
waterproofing placed behind a construction joint will prevent leak- 
age of water into and through the joint. It would be better to make 
the joint follow a straight horizontal line flush with the bottom or 


18 


soffit of the deck girders. 

Another detail for 
bridge seats with fixed 
bearing is shown under 
Joints in Decks. 


FIG. 17 


When the spans are 
long, say 50 feet or more, 
the deflection of the deck 
may rotate the ends of the 


girders so much that the 


bearing pressure may be- FIG. 16 Bridge seat used by Wisconsin High- 
way Commission. The deck and the abutment 
come concentrated on a gre not shown in their proper relative position, 


narrow strip along the front but the dotted lines and a-a indicate how deck 
edge of the seat and cause and abutment fit together. 
local damage. 

Double steel plates, as illustrated in Fig. 17, are suitable for long 
girders. The top plate is fastened to the superstructure and the bot- 
tom plate to the bridge seat. One plate has a convex bearing surface, 
so that it can rock on the other as the girders deflect. Sliding be- 
tween plates may be prevented by use of heavy pins tapped into the 
bottom plate and extending through conical holes in the top. 

Various details are used at expansion bearings. Layers of tar 
paper are often the only expansion device inserted between the 
bridge seat and the deck. The efficiency of this detail is question- 
able, as it has been observed that a number of tar paper expansion 
bearings show no evidence of consistent relative movements. 

Two plane pilates attached to 
the bridge, one to the seat and 
one to the deck, are also used at 
expansion bearings—often sepa- 
rated by a thin layer of materi- 
als such as graphited asbestos, 
zinc or copper to reduce friction. 
For long spans a detail similar 
to that in Fig. 17—consisting 
of a plane and a curved steel 
plate, but without pins—may 
be suitable. A construction 
using a roller or rocker placed 4¢.. 
between two steel plates has the * 
advantage of insuring more posi- FIG. 17 Bearings on pier illustrating the 
tive and longer lasting freedom 8° of plane and convex bearing plates. 


Quite evidently these plates were not 
of movement. accurately placed. 


19 


"a 


f? 
: & 

s 

i 


see | ; 


Bearing 
Plates 


Expansion 
Bearing 
Details 


Importance 
of Freedom 
of Movement 


Protecting 
the Bridge 
Seat 


There is considerable doubt as to the permanency of the freedom 
of movement in many types of expansion bearing. Corrosion of 
the metal or decomposition of other materials may ultimately 
interfere with the regular sliding action. The expansion bearings 
are then said to be ‘“‘frozen’”’ and the structure behaves as if the 
deck had fixed bearings. This condition is relieved somewhat by 
the use of cast iron or non-corrosive metals such as stainless steel 
and bronze alloy. 

The bridge seats should be kept free from dirt and moisture 
from the approach fill. At fixed bearings this may be accomplished 
by placing a strip of membrane waterproofing on the rear face of 
the abutment. Both the angular and horizontal movements here 
are so small that there is no danger of rupturing the fabric. In 
other cases, the breastwall is extended up past the end of the deck. 
Details involved in this type of construction are discussed under 
Joints in Decks. 


Feat is 
Maes 25 
ee es 


ee: , 
; pelt 
. a, 


t 
(3 
Yi 
4 
3 
j 
4 
; 
Yj 
4 
; 
Yj 
Z 
/ 
Y 
4 
; 
w. 
A: 
A: 
A: 
A: 
Z 
4 
y 
H 
4 
; 
; 
; 
4 
j 
4 
; 
4 
Hi 
y 
HA 
A: 
As 


id 


Abitmen 


FIGS. 18-19 Sketches showing relative movements at expansion bearings. The sur- 
face marked A, which is part of the deck, was originally flush with the surface marked 
B, which is part of the abutment. The abutment then moved and created an offset 
between A and Bas indicated by the area marked C. The deck slid on the expan- 
sion bearing, the amount of sliding being indicated by the arrows. The abutment 
has moved backward in Fig. 18 and forward in Fig. 19. 


20 


Bridge roadways are usually crowned, and it is often desirable 
to build all deck girders of equal depth under the roadway to 
simplify bar details and formwork. It is expedient in such cases 
to step off the bridge seat as shown in Fig. 12. This detail is 
discussed further under Creep in Skew Bridges. 

Cantilevered sidewalk slabs should usually be separated from 
abutments by wide joints filled with a soft joint filler. Otherwise 
the slabs may crack. 


ABUTMENT MOVEMENTS 


Vertical and horizontal displacement of the footings causes rela- 
tive movements of abutments with respect to the deck. This 
creates critical strains in the abutments, in addition to the strains 
caused by structural action already discussed. 

It is usually difficult to ascertain by field inspection whether 
and how each abutment moves. The only visible evidence of 
movement is at the expansion bearing, and this shows only the 
combined movement of both abutments. The most common 
movement of an abutment, of course, is forward toward the deck. 


FIGS. 18 and 19 


Fig. 18 shows how abutments may move relative to the deck. 
Here backward movement of one or both of the abutments is 
indicated. Evidence of forward movement is presented in Fig. 19. 
The width of the dark area of shadow (C) represents the total 
movement in both abutments. The original clear distance between 
the abutments has evidently been shortened by about 4 inches. 

It is probable that the deck in Fig. 19 now bears against the 
backwall of the abutment. If so, no further movement will take 
place, but at the same time the expansion bearing will act partly 
or even wholly as a fixed bearing. The structure will then behave 
not according to type a in Fig. 14 but as type 0, and the abutments 
will act as vertical beams or slabs supported by the deck and by the 
footing. 


FIG. 20 


It is usually difficult to detect cases where concrete decks are 
jammed between the abutments, and attempts to release the deck 
are rarely made in concrete structures. In some cases involving 
other types of structures, the deck was observed to be wedged 
tightly between the backwalls of the abutments, thus creating a 
horizontal thrust in the deck structure. Fig. 20 illustrates a case 
in which the backwall is punctured in order to relieve thej;deck 


21 


Stepping-off 
the Seat 


Evidence of 
Movements 


Deck 
Jammed 
between 
Backwalls 


Wet and Dry 
Backfill 


Pressure 


Precautions 


of the thrust and permit it to 
“breathe.” 

Abutments are usually pro- 
portioned to withstand the ac- 
tive earth pressure from dry 
backfill only, assumed to be 
equivalent to the pressure ex- 
erted by a fluid weighing 30 
pounds per cubic foot. 

If the backfill behind the 
abutment becomes saturated, it 
will exert a pressure which may 
be more than twice as great as 
that assumed in the design. As 
a result, the abnormally high 
pressure of wet backfill causes 
harmful effects by making abut- . 
ments tilt or move forward as a 
whole. For this reason, back- FIG. 20 Abutment backwall purposely 
ills generally should not be Rytied,tollew the superstructure to 
jetted but should be placed and ment of abutments is seen at the expan- 
compacted without the use of _ sion bearing. 
water. 

The following precautions should be considered where move- 
ments of abutments are anticipated. The front face of the abut- 
ment should be given a slight batter in order to avoid the ugly 
appearance accompanying a forward tilt. The backfill should 
preferably be of a coarse material or any other material that quickly 
releases entrapped water. The abutment should be designed as 
usual as a cantilever and also in many instances as a vertical beam 
supported at the foundation and at the bridge seat; this requires 
vertical bars at both faces. It may be advisable under unfavorable 
circumstances to make a special investigation of the stability of 
the abutment for an earth pressure 2 or 3 times greater than the 
active pressure assumed to be exerted by dry backfill. 


JOINTS 


The correct location and proper construction of joints are of 
great importance in bridge building. The ordinary concrete bridge 
structure is composed of various elements, each of which may 
expand or contract. In addition, adjacent elements may have a 
relative movement which is often imperceptible but may become 
destructive if the joints are not properly designed. 

A construction joint is created where the casting of the con- 


22 


crete is temporarily discontinued. Designers should show the 
position of the construction joints on the drawings, and no addi- 
tional joints should be allowed in the field except by special per- 
mission. 


It was often observed during the survey that water seeped 
through horizontal construction joints in abutments, that the seep- 
age had caused damage, and that concrete abutments without 
joints were more durable. If horizontal construction joints must 
be used, and the concrete is placed in “‘lifts,’’ special precautions 
must be taken. Additional dowels should be placed across the joint 
and a strip of membrane waterproofing should be placed behind 
the joint. Most important of all, the concrete must be uniformly 
dense and non-absorbent throughout the entire height of each lift. 
It is best, whenever possible, to avoid having any horizontal joints 
in abutments between the bridge seat and the top of the footing. 


In case a coping is used immediately below the bridge seat, the 
concrete should be placed up to the underside of the coping and 
concreting then discontinued for a time only sufficient to permit 
the concrete to settle before the coping is cast. This, however, 
does not constitute a regular construction joint. 


FIG. 21 


Construction joints should 
have a small groove on all ex- 
posed surfaces wherever pos- 
sible. This will make the joint 
neater and prevent spalling. Fig. 
21 illustrates the typical appear- 
ance of a construction joint that 
is left plain compared with one 
that is grooved. Note the su- 
perior appearance of the grooved 
portion. 


Joints other than ordinary 
construction joints may be clas- 
sified either as ‘contraction 
joints” or as “expansion and 
contraction joints.”’ The simple 
terms “‘contraction joints’ and 
“expansion joints’ are often used. 
Different modifications of these FIG. 21 Note the contrast between the 
joints are used in abutments, unsightly ungrooved portion of this con- 


=o struction joint and the neat triangular 
decks and handrailings. groove. 


23 


General Con- 
siderations 


Plain or 
Keyed 


Doweled 
Joints 


JOINTS IN ABUTMENTS 


To prevent seepage, all construction or contraction joints should 
be protected by a strip of membrane waterproofing. The fabric 
will not tear because the reinforcement is continuous across the 
joint. Fabric waterproofing should not generally be used at expan- 
sion joints; seepage must here be prevented by other means. 


FIG. 22 


For contraction joints in abutments, the plain grooved type— 
ain Fig. 22—is usually adequate. If there is any danger of relative 
horizontal movement or sliding, a key-and-groove joint as shown 
by bin Fig. 22 is preferred. 

The small groove illustrated in Fig. 21 appears from observation 
to be adequate. If an appearance involving rustication is desired, 
a larger groove is often used, as indicated in Fig. 12 (page 16). 
White lead paint is sometimes brushed on the concrete in places 
where it is desirable that a construction joint should open. 


The plain joint and the key-and-groove joint shown in Fig. 22 
are usually the only types that are needed in breastwalls less than 
50 feet in length. It appears that normal contraction of the con- 
crete can be accommodated if the joints are spaced not more than 
15 to 20 feet apart. 


Construction Joints 
Reintorcing bars 


oi 0. a G- rete 


| = emo Ste 


FIG. 22 Horizontal sections of a plain and a key-and-groove construction joint used 
in abutment walls. The reinforcement extends across the joint. 


FIG. 23 


The modification of this type of joint shown in Fig. 23 is some- 
times used and with good results. Short dowels, about 60 diameters 
long, are the only reinforcing bars that cross the joint. One-half 
of the length of the dowels is embedded in the concrete first cast; 
the other half of the dowels is either greased or placed within 


24 


Membrane waterprooting thin-walled tubes (of metal or 
: fiber) before concreting is re- 
sumed. The width to which the 
crack may open is not restrained 
by any reinforcing bars except 
@ Construction joint by those in the footing. The 
— membrane waterproofing may 
Ree ae therefore tear unless it is placed 
with a fold at the joint as indi- 


FIG. 23 Horizontal section of vertical cated in Fig. 20 or two separate 
construction joint sometimes used in 


abutments. The dowels are bonded to Strips may be overlapped at the 
the concrete on one side only. joint. The action of the dowel 

bars in this detail is similar to 
that of the key-and-groove construction shown in Fig. 220. 


ove 


OA brs vo. 
rian 


FIG. 24 


The typical feature distinguishing an expansion joint from a 
contraction joint is that the concrete in the latter is cast directly 
against concrete in the joint, whereas in the expansion joint the 
abutting concrete surfaces are separated by a filler. The function 
for which the joint is designed determines the thickness of the filler; 
it is usually between 4% and linch. The expansion joint is suitable 
for cases in which expansion as well as contraction is anticipated. 
It should be observed that “‘expansion”’ in abutments is rarely due 
to swelling of the concrete but is caused by movements such as 
creep or settlement. 

In abutments, the watertight expansion joint construction 
shown in Fig. 24 is usually satisfactory. The exposed edges should 
be chamfered and seepage prevented by inserting a bent strip of 
16-ounce copper plate. The copper strip may be placed as in a 
to prevent water from penetrating the joint. A neater appearance 
is obtained by placing the copper as in 0. 


Joint filler 
Metal water stop 


FIG. 24 Horizontal sections through expansion joints suitable for use in abutments. 


25 


Expansion vs 
Contraction 
Joints 


A 
Watertight 
Joint 


Importance 
of Preventing 
Seepage 


FIG. 25 z inch Hard Joint filler 

The key-and-groove con- 2: aera oR ee 
struction may be incorporated 
in the expansion joint detail as 
shown in Fig. 25. The lip out- 
side the groove has been known 
to be damaged by cracking 
along the dotted line shown. 
Care should therefore be taken 


to make the lip sufficiently thick 


FIG. 25 Horizontal section through ex- 
2 : pansion joint with key-and-groove con- 
and to reinforce it properly. shbcton 


JOINTS IN DECKS 


It is now generally agreed that water must be kept from seeping 
through joints in decks. This requirement has in the past been 
violated in a great many cases. 


FIG. 26 


Seepage is commonly observed and water stains often mar the 
beauty of bridges, as illustrated in Fig. 26. Moreover, failure to 


FIG. 26 Seepage through deck joint has caused unsightly water stains and may 
damage the pier cap. This illustrates the need for proper joint details. 


26 


prevent seepage through joints and cracks is responsible for a 
good deal of local damage in otherwise durable structures. 

Drenching of ordinary concrete due to rain is not harmful. 
For illustration, the handrailing in Fig. 26 shows no evidence of 
disintegration or signs of water stain. It is slow and constant 
seepage that may be harmful. Good, dense concrete is durable 
even when constantly or intermittently wetted, but inferior porous 
concrete may be damaged by slow seepage. Concrete mixes with 
low water-cement ratio* are essential for exposed structures since 
such mixes are dense and practically non-absorbent. 

Especially destructive is the combination of conditions in which 
(1) constant seepage takes place through a (2) porous concrete 
where the climate has (8) frequent cycles of freezing and thawing. 
Prevention of local damage therefore depends upon the two follow- 
ing safeguards: seepage through joints and cracks should be pre- 
vented, and the concrete must be made dense and non-absorbent. 


FIG. 27 


Construction joints in decks should be avoided as much as 
possible. If used, they should be detailed so that they do not 
develop cracks through which water may seep. They should 
preferably be placed along lines crossing the greater amount of 
reinforcing bars. It is particularly advisable to add dowels across 
the joint near the top surface as shown by a in Fig. 27 in order to 
help the regular reinforcement keep the crack closed. The edges 
hould have a small bead, as in a, to prevent scaling. The groove 


Groove filled with mastic-¥ 


Ce i? F Mee 


a 
FIG. 27 Joints suitable for concrete decks. The joint in type a may be keyed and 
is used where the reinforcement is continuous, while type b is used where the rein- 
forcement is not continuous. 


*A complete discussion of the basic principles involved in making durable concrete is given in 
“Design and Control of Concrete Mixtures”’ available free in the United States and Canada upon 
request to the Portland Cement Association. 


27 


Most 
Destructive 
Conditions 


Adjacent 
Fixed 


Bearings 


Expansion 
Joint 
at Piers 


Treadplates 


should finally be covered with mastic. A key-and-groove joint is 
often specified. 

In Fig. 27, b represents a joint between two simply supported 
deck spans with adjacent fixed bearings on the pier. Although 
the two decks have no relative horizontal movement, it is inadvis- 
able to omit the joint filler. The reason is that the deflection of 
the spans may rotate the ends of the decks and thus open the 
joint sufficiently to admit water, and yet the crack may be so small 
that it is difficult to calk. The use of a thin sheet of joint filler 
(b in Fig. 27) is preferred. As the need arises, the filler may be 
driven tightly into the space between the abutting concrete sur- 
faces. The use of a small bead on the edges is good practice. 


FIG. 28 


The number of deck expansion joints should be kept as low 
as possible—for example, by judicious arrangement of fixed and 
expansion bearings in multi-span bridges. 


Three major requirements must be fulfilled at expansion joints. 
Sufficient space must be provided for relative movements; the gap 
between adjacent sides of the joint must be bridged in order to 
avoid roughness in the wearing surface; and water must be kept 
from leaking through the joint. 


The two joints sketched in Fig. 28 are representative of the type 
found to be serviceable for use in bridge decks. Detail a in Fig. 28 
is suitable for use in sidewalks or pedestrian bridges. It embodies 


Bearing plate ie plate Groove Filled with mastic. 


Or Ol Oe 


Sidewalk Oeta// 


toy 
Ion 


FIG. 28 Two types of devices used at expansion joints in concrete decks. Type a 
has been used successfully on sidewalks, while type b is preferred on roadways, 


28 


two plates—a treadplate and a bearing plate—anchored to the 
concrete on opposite sides of the joint. The attachment of the 
plates, a in Fig. 28, is not sufficiently substantial for use in road- 
ways. Detail b, embodying two plates and two angles, is preferred 
for ordinary highway traffic. Treadplates are preferably attached 
to the uphill side of the joint, and the groove between the plates 
is filled with mastic in order to reduce seepage of surface water. 
Drips indicated at the bottom of the slabs in Fig. 28 may help 
keep water from running down the sides and across the bottoms 
of beams and girders. 


FIG. 29 


Treadplates are often attached to the angle below by means 
of rivets with heads countersunk in the roadway surface. Some 
designers recommend the use of tap screws instead of rivets to 
facilitate removal of the treadplate in case it must be replaced. 
It is possible, however, that corrosion may prevent the removal 
of the tap screws. It may therefore be advisable, for future use, to 
provide some intermediate threaded holes in the angle and to fill 
the holes with grease. The appearance of an expansion device 
similar to } in Fig. 28 is illustrated in Fig. 29. 


Great care is required in planning expansion joint details. 
First of all, it should be ascertained that sufficient ome is pro- 
vided throughout the deck for 
movements that may take place 
in the joint. The handrailing, for 
example, should beso constructed 
that there will benocontactacross 
the handrail joint even if the 
deck joint is completely closed. 
The girders should always be so 
built that they will bear against 
each other before any other con- 
tact is possible. It is important 
that the metal shapes be care- 
fully placed and securely at- 
tached so as to avoid roughness 
in the roadway surface. The 
treadplate should be made to 
bear tightly against the metal men 
shape underneath, since failure FIG. 29 Treadplate at expansion joint 
to do so often causes the metal nconerladeck sla, This deck has one 
shapes to become looseandrattle. — surface. 


29 


Allowance 
for Expansion 


Deck Joint 
at Fixed 
Bearing 


FIG. 30 


The joints at the ends of the deck must be detailed to fit into 
the entire layout at the top of the abutment. There are three 
main elements to consider: namely, the support of the approach 
slab (usually of reinforced concrete), the support of the deck (which 
is either a fixed or an expansion bearing, but preferably a fixed 
bearing), and watertightness of all joints involved. 

Fig. 30 shows an ar- 
POT So ge ae with ginal: ie rangement for a deck sup- 
seg ee Gee ported by a fixed bearing 
7 on the seat of an abutment. 
Dowels between the deck 
and the breastwall make 
it a fixed bearing, and the 
ridge on the bridge seat 
acts to counteract the tend- 
ency of the abutment to 
move inward under the 
deck. The strip of mem- 
brane waterproofing is 
added to insure watertight- 
% 4 ness in the horizontal joint. 
FIG. 30 Isometric view illustrating bearing Some designers recommend 
org Soe ye eg sod at Ronse Cae the use of vertical dowels 
aa He foried auhe decktecnersia only i tying the approach slab to 
the seat to prevent the 
approach from being lifted off its seat when the slab is jacked up 
with a mud-pump. It appears that the vertical dowels will interfere 
with the placing of the membrane waterproofing. It is therefore 
suggested that they be placed horizontally as indicated in Fig. 30. 
This arrangement has the added advantage of helping to keep 
the vertical joint closed and watertight. If the dowels are omitted, 
the use of a joint filler is recommended for watertightness. In Ohio, 
the Bureau of Bridges successfully uses fixed supports similar to 
that of Fig. 30 at both ends of slab deck spans up to 25 feet long. 
In the case of deep deck girders, the construction in Fig. 30 may 
be modified to allow a bearing ledge in the deck for the approach 
slab. 


Breastwa// 


FIG. 731 


The details are different when the deck is allowed to move 
longitudinally on an expansion bearing. It is then necessary, in 
order to keep the bridge seat clean and dry, to provide a backwall 


30 


Se 


WeBananauceul oo Cie 


Backwal/ 


N 
N 
I 


SSS ¥ 


Sheet of Zinc or lea 


. ge bearing 
ach “ON briage seats 


Breastwall 


eZ 


FIG. 31. Two arrangements of joints at the expansion end of concrete decks. The 
backwall is extended to the roadway surface in type a, while it stops at the bottom 
of the slabs shown in type b. 


by an extension of the breastwall up past the end of the deck as 
shown in Fig. 31. 


When the top of the backwall is at the bottom of the approach 
slab, as shown in 8, Fig. 31, only one joint appears in the deck. 
Deck expansion devices similar to those in Fig. 28 may be used to 
bridge the gap in the joint, or a simple joint may be used. The 
joint is placed near the middle of the backwall, the deck slab is 
cantilevered backward to this joint, and a sheet of lead or zinc 
(bent as shown) may be used under the two slabs to reduce the 
friction. 


The construction in which the top of the backwall is made flush 
with the roadway surface is also commonly used, but makes two 
joints in the roadway surface. The main joint (at the deck) is 
usually of the type embodying joint filler and copper strip for water- 
tightness. 


FIG, 32 


The water stop may be one of the types shown in Fig. 32. 
The secondary joint at the approach slab needs only a thin sheet 
of joint filler. The use of the copper strip at deck expansion joints 
that close and open at frequent intervals has been unsatisfactory 
in some instances. The copper was found to be cracked due to 
fatigue from being frequently bent in opposite directions. For this 
reason it may be advisable to use a construction without water stop 


31 


Deck Joint at 
Expansion 
Bearing 


Crown and 


Gutter Grade 


Inlets 


and to give preference to a 
detail similar to that shown 
in Fig. 316. It should be 
noted that water stops of 
the type in Fig. 32 are sat- 
isfactory for expansion 
joints in abutments where 


th 1 FIG. 32 Two types of water stops that are used 
€ movements are so sma to make joints watertight. The perforations are 


and infrequent that there designed to permit greater bond between the 


is little chance of rupture concrete on the two sides of the sheet. 


due to fatigue. 


DRAINAGE 


Surface water on bridge decks should be disposed of as quickly 
and directly as possible. This is accomplished by crowning the road- 
way and building gutters to drain into inlets. 


All bridge decks not superelevated should have a crown. A 
114-inch crown in 20 feet of roadway width is usually sufficient. 
For widths equal to VY (in feet), the rise of the crown (in inches) 
may be made equal to 14% + % Xx a In general, the crown 


on a bridge shall be consistent with that on the adjacent highway. 


Sufficient pitch in the gutter can be obtained in several ways. 
The roadway on the bridge may be built on a grade, or with a 
longitudinal camber, or the pitch may be built into the gutter 
itself. Some designers prefer always to build bridges with greater 
longitudinal camber than that required to offset the load deflec- 
tion. They maintain that it 
improves drainage and im- 
parts a definite impression 
of strength by killing the 
appearance of sag. 

The drain inlets should 
be spaced to suit the gen- 
eral layout and should be 
so constructed that the 
water is not discharged 
against beams, girders, 
piers or abutments. 


Neither should water be FIG. 33 Two types of scuppers used for drain 


: inlets. The shape of the scuppers is designed to 
permitted to seep along the prevent the drain water from touching the con- 
bottom surface of the deck. crete. 


32 


mera) 
oe a S 


EiG=a33 


Fig. 33 shows typical 
details of cast iron scuppers 
commonly used for drain 
inlets. A clean discharge 
is obtained in Fig. 33) by 
extending the scupper a 
few inches below the deck. 
The scupper should never 
be stopped flush with the 
bottom of the deck. The 
direction of the water dis- 
charge may be controlled 
by use of a scupper type as 
shown in a. 

In some instances water 
has been removed from 
the gutter by placing hori- 
zontal drain outlets through 
the curb, thus discharging 
the water over the surface 
of the fascia girders. This improper practice is being definitely 
discouraged by the Bureau of Public Roads. 


x S Laey WR CEE REP ERY Oo 
a4 . , ee groove on 
three sides of inlet 


mi ‘Bent jf inch plate 


Girder 


FIG. 34 Self-clearing type of drain inlet with 
grate and scupper. 


FIGS. 34 and 35 


The drain inlets shown in Fig. 33 are often considered too 
small, especially where there is danger of the inlets becoming clogged 
with ice. The construction sketched in Fig. 34 is then pre- 
ferred. It combines an overflow 
arrangement with a large open- 
ing covered with a detachable 
cast iron grate. This type of 
inlet rarely becomes clogged. 
Note that the steel plate at the 
overflow is so constructed that 
drainage water is deflected away 
from the girder. 

This type of drain inlet is 
also illustrated in Fig. 35. 


3 
x The b: a oer ae = sa ¢ gear oes 


FIGS. 36 and 37 


FIG. 35 Drain inlet with large grate and 


overflow arrangement. Note that tap : 
screws attach the grate to the frame Water should not be dis- 
underneath. charged upon a railroad bed, 


33 


Disposing of 
Surface 


Water 


Various 
Types 


¥. i : i F id Sore ae 


FIGS. 36-37 Concrete gutter and sodding protect embankment slopes against ero- 
sion. Eroded slopes detract from the appearance of bridge structures. 


roadway, sidewalk, or earth embankment slope around the abut- 
ment. If necessary, concrete troughs should be built on the slopes 
under the drain inlets to avoid erosion. It is good construction to 
extend deck curbs and gutters along the approach roadway to a 
point where the drain water may be safely taken down the slopes in 
concrete lined gutters, as illustrated in Fig. 36. Erosion due to 
inadequate provision for drainage on the approaches is commonly 
observed (see Fig. 37) and is unsightly. 


Rip-rap on the embankment slopes below the normal water 
line, and sodding above it, will lower the cost of upkeep and improve 
the appearance of the bridge. 


WEARING SURFACE 


There is a noticeable dissimilarity in the present practice of 
applying waterproofing and providing the wearing surface on top 
of the structural slab. The following constructions are used: 
(1) Slabs without wearing surface. (2) One-course construction 
in which the wearing surface (usually less than 1 inch thick) is cast 
integrally with the structural slab. (8) Wearing surface cast 
directly on top of structural slab using two-course construction- 
(4) Wearing surface separated from structural slab by waterproofing 


34 


without fabric. (5) Wearing surface separated from structural slab 
by membrane waterproofing. 


The cost increases approximately in order from type (1) to (5). 
Observations in the field indicate, however, that the durability 
decreases in the same order. Type (1), for example, appears to be 
the most durable and at the same time the most economical con- 
struction. The Bureau of Public Roads feels that additional 
thickness for wearing surface is unnecessary except possibly in a 
few cases such as in regions where there is considerable heavy chain 
traffic during particularly long periods. 


Separate concrete wearing surfaces are built with an average 
thickness of about 4 inches. If the finished surface is to be crowned, 
the top of the structural slab is usually given the same crown. 


It has been customary to construct joints in the wearing surface 
at the following places: (a) along the centerline of the roadway, or 
between the lanes on bridges with more than two lanes; (b) over 
the regular deck joints, and transversely at intermediate lines in 
some cases on long spans. In such cases, the total length of the 
joints in wearing surfaces is therefore increased over the length of 
joints in the structural slab underneath. This is an objectionable 
feature since deck joints are relatively weak and apt to be dam- 
aged. The tendency now is therefore to use as few joints as possible 
in the wearing surface. 


The main sources of damage are (a) impact due to wheels 
passing the joints, and (b) curling of the separate wearing surface 
in the vicinity of the joint. Free water between the two ‘courses 
near the joints was observed during the removal of a top course. 
It was evident that the water had seeped through the joints in the 
top course and had penetrated through some distance adjacent to 
the joint, the water being retained on top of the waterproofing. 
The consequence was that the top course shrank non-uniformly 
so that its top surface became slightly concave. Freezing of the 
entrapped water may have contributed to this condition. The 
curling was most pronounced at the intersection of two joints be- 
cause the seepage was greatest. The load and impact from passing 
vehicles then broke the corners. 


Curling and seepage are eliminated when the wearing surface 
is built integrally with a structural slab or omitted entirely. That is 
why the one-course bridge deck is more durable than the two-course 
construction. If two courses are used, care should be taken to 
develop the best possible bond. 


Observations made during the survey pointed to the conclu- 
sions that (1) cracking in one-course construction is negligible and 


35 


Location 
of Joints 


Causes of 
Cracking 


Advantages 
of One- 
course 
Construction 


(2) cracking occurs most frequently in the construction consisting 
of two courses separated by waterproofing. 

The use of one-course deck construction, despite its economy 
and durability, has not yet become universal. In this connection it 
should be observed that separate wearing surfaces are used, not 
primarily as a means whereby bridge decks may be waterproofed, 
but mainly in order to facilitate the construction operations. Ex- 
cellent workmanship, however, was observed in a great number of 
bridge decks with one-course construction; the lines were true and 
the surfaces even. 


HANDRAILINGS 


No part of a bridge is more conspicuous and at the same time 
more exposed to variations in temperature and moisture than hand- 
railings. Careful attention should be given to their detailing and 
construction, to which the following rules are considered generally 


applicable. 
FIG. 38 
EstheticuCoas A pleasing proportion between the general aspect of the railing 
siderations and the bridge proper is esthetically desirable. For example, a 
Parattin Joints 
3 inch wide ormore ey 
mes 

rein ie [sere by 

bat ey, Se 

ia YS 

/ aS = 

SES <Q 

@ D eats 

See Sen er a Sa 

mS HS AS Qk 

ay Waker t (sucrose cael (eee Lal Pee) oy 

SS) 

| a eS aya ie ae PS 

pose Dual GPE 
COIL Yar nat Cock Top of sidewalk: sees ees 

FIG. 38 Handrailings with precast Ree are ies preferred and have a pleasing 

appearance. 


36 


solid handrailing is preferred for spandrel filled arches while the 
open railing type is better suited for use on open spandrel arches. 
According to the same rule, a well balanced appearance is obtained 
by using an open railing on the span over the bridge opening and a 
solid railing on the wingwalls. Handrailings with precast spindles 
as shown in Fig. 38 and Fig. 39 are particularly suitable for bridges 
in urban regions. 


Sogamear enemas acon Se aN 


FIG. 39 Handrailing on two-span arch bridge. The post over the pier is carefully 
jointed on each side. Note the wind-slot below the footrail. 


FIG. 39 


Precast concrete spindles for railings of the type illustrated in 
Fig. 39 have occasionally been observed to differ in texture from 
the rubbed surfaces of adjacent cast-in-place concrete. Suitable 
molds and materials should be chosen for precast spindles in order 
that their texture may conform to that of the surrounding concrete. 


In regions with heavy snowfalls, handrailings are often designed 
to be as open as possible to minimize drifts and facilitate snow 
removal. 


The use of solid handrailings is sometimes advocated for spans 
over railroad tracks in order to prevent smoke from discoloring the 
inside of the railing. Fig. 40 illustrates an open and a solid hand- 
railing design, the latter being on a span over a railroad. 


37 


Snow, 


Smoke, Wind 


Spindle 
Details 


FIG. 40 Handrailing illustrating open 
joints, split post, wind-slot, and solid 
railing over railroad track. 


FIG. 40 


Some designers advocate the 
use of an open space between 
the top of the sidewalk and the 
bottom of the railing panels as 
illustrated in Figs. 38, 39 and 40. 
The draft through the wind-slot 
thus created has been found to 
assist materially in keeping the 
sidewalk free from snow, leaves 
and debris. The slot is not used 
in railings placed on curbs. 


FIG. 41 


It is advisable to delay the erection of handrailings until after 
the falsework has been struck and the deck has taken the major 
part of its dead load deflection. This applies particularly to arches 


with long spans and to all spandrel filled arches. 


If this pre- 


caution is not taken and the joints are made too narrow, com- 
pression may be set up in the handrailing. The result may be that 


the joint filler is squeezed out as 
illustrated in Fig. 41 or the com- 
pression may ultimately cause 
spalling of the concrete at the 
joints. 

If the spindles are pre-cast, 
it is not advisable to provide a 
depressed pocket for them in the 
top of the footrailing, because 
water may be retained and may 
freeze in these pockets. It is 
better to make the surface plane 
or even to provide a raised pad 
slightly larger than the size of 
the spindle. A dowel bar is 
usually placed through a hole in 
the center of the pre-cast spindle 
as shown in Fig. 38. 


FIG. 42 


Sharp re-entrant angles tend 
to start cracking, particularly in 


38 


Ed ~ 


FIG. 41 Handrailing on arch bridge 
showing extruded joint filler. 


=e sale yy 's ae eae o ee Roadway slab SO ae a Ae, 


FIG. 42 Handrailing with re-entrant angles may develop cracks as indicated in 
type a. It is better to make the apertures rounded as shown in type b 


handrailings, because of severe exposure. For illustration, the 
type of railing shown in Fig. 42a often develops cracks as indicated, 
and the construction shown in Fig. 420 is preferable. 


FIG. 43 


Handrailings are frequently divided into panels by posts spaced 
about 7 to 12 feet apart. An odd number of panels in a bridge span 
is esthetically preferable to an even number. The type of post 
shown in Fig. 43a is unsatisfactory both from appearance and dura- 
bility. A post detail as shown in Fig. 480 is better. 


4 phd filler 


ie! ee ee ee 


FIG. 43 The post detail in type a appears to be too stubby and the off-set joint is 
objectionable. The post in type b has better proportions and has been used success- 
fully with open joints. 


FIG. 44 


The regions of the railing above the abutments and piers are 
commonly accentuated by use of an exceptionally large post. The 
jointing of this post needs careful attention. A common joint 
arrangement at a pier is to attach the post to one side of the joint 


39 


Design of 
Panels and 
Posts 


Types of 
Joint Filler 


Open joints Qpen Jyn 45 


peck slab | ‘ne 
POT ORE: cgatidctd 


Sas ee! | Be wi rae 


- ‘Deck Slab : 


ee 19. 


Joint in deckA7 


FIG. 44 Post details suitable for use at deck joints over piers and abutments. Type a 
has one undivided post attached to one side of the joint, while type b has two posts 
separated by an open joint. 


in the deck and let it cantilever over the deck on the other side of 
the joint. This is shown in Fig. 44a and Fig. 45. Care must be 
taken to provide sufficient space in the joints, particularly in the 
horizontal joint above the curb. It is best to make the horizontal 
joint with an open space about 34 inch wide. There is now a tend- 
ency to avoid the cantilevered type of post and to split the post 
into two symmetrical halves, each of which is attached to the deck 
on its respective side. This arrangement is shown in Fig. 44} 
and Fig. 40. 


FIG. 45 


The appearance and durability of a handrailing depend a good 
deal upon the type of material used for joint filler. White lead paint 
or paraffin brushed on in several thin layers has been used for joint 
filler in special cases, but such joints are often too narrow. Among 
other materials used are pre-molded bituminous joint filler, sponge 
rubber, and cork board. The requirements for good joint filler 
should be still more exacting than those for joints in abutments, 
because good appearance is of greater importance in railings. The 
best results are usually obtained by using no joint filler at all and 
by providing an open space wherever the railing must be jointed. 
A 34-inch width is usually sufficient except at deck expansion 
joints, where the width should be made at least equal to the width 


40 


of the joint in the deck. Open 
railing joints have been used 
successfully on a great number 
of bridges. 


The construction of hand- 
railing with inadequate lateral 
strength constitutes a distinct 
hazard, and reasonable strength 
should be required to prevent 
automobiles from breaking 
through the railing. For this 
reason the Bureau of Public 
Roads favors the requirement 
that railings shall be designed 
to withstand safely a lateral 
pressure of 500 pounds per linear 
foot applied to the railing at a 
point about 2 feet above the 
roadway surface. For the sake 
of safety, the Bureau of Public 
Roads strongly recommends 
smooth inside surfaces without 


FIG. 45 End post in handrailing sup- 
ported on abutment. Note that the hori- tate : : ae 
zontal joint above the deck slab is open. projections, especially in railings 


on curbs adjacent to the road- 
way. 


CREEP IN SKEW BRIDGES 


Many bridges are built with an oblique angle between the direc- 
tion of the roadway and the direction of the piers or abutments. 
These so-called skew bridges have some characteristic features that 
are generally given little attention in detailing and construction. 


FIG. 46 


Numerous observations revealed that the longer diagonal of 
skew bridge decks had a tendency to lengthen during a long period 
of service. The most distinct evidence was usually observed at the 
expansion bearing, where the deck had moved laterally upon the 
bridge seat in the direction toward the acute angle of the deck as 
indicated in Fig. 46. 


Lateral creep has been observed to amount to as much as 4 
inches. Even much smaller movements may cause damage. In 
single-span bridges, for example, the pressure accompanying the 


41 


Lateral 
Strength 


Observed 
Lengthening 
of Longer 
Diagonals 


Evidence 
of Creep 


FIG. 46 Plan view of skew bridge illustrating how the long diagonal tends to elon- 
gate. The free end then creeps laterally on the expansion bearing as indicated. 


movement may be great enough to break a large piece out of the 
wingwall and displace it several inches. Fig. 47 is a sketch of 
possible damage to an abutment through failure to prevent creep 
in a skew bridge. Note that the damage is greatest at the bottom 
of the abutment where it is restrained from moving. 


FIG. 47 


It may be significant 
that the crack at the end 
of the bridge seat in Fig. 
47 resembles very closely 
cracks ¢ in Figs. 3 and 6a. 
The crack in Fig. 6a and 
the damage in Fig. 47 may 
represent different stages 
in the development of dam- 
age done by creep. Creep : pune 
may possibly be another FIG. 47 Abutment damaged by creep at ex- 


reason for cracks like c in pansion bearing in skew bridge. It is evident 
Fig. 3 that creep is accompanied by great forces. 


FIGS. 48 and 49 


In some instances, the evidence reveals creep at the expansion 
bearing of the deck. For illustration, the multi-span bridge shown 
in Figs. 48 and 49 has one expansion and one fixed bearing on each 
pier. The offsets in the curb line illustrated in Fig. 48 show a creep 
of about 114 inch in each expansion bearing. This creep can also 
be observed in Fig. 49, which shows a close-up of part of the joint 
in the sidewalk on the same bridge. 


42 


FIGS. 48-49 Skew multi-span bridge exhibiting creep at expansion supports. Note 
offset of about 11% inch in curb at each pier (left) and increase in width of joint in 
sidewalk (right) both caused by creep. 


FIG. 50 


The evidence of creep is usually overlooked in the early stages. 
For example, little attention may be given to conditions such as 
that illustrated in Fig. 50, which shows that the joint filler has 
been squeezed out at the acute angle of the deck at the expansion 
bearing. This was caused by creep. The combined resistance 
furnished by the friction in the expansion bearing and by the strength 
of the concrete in the wingwall has apparently been sufficient to 
check further creep. 

It is not advisable to disregard the phenomenon of creep in 
skew bridges or in bridges on curves and thus to permit wingwalls 
to be subjected to a considerable thrust they are not built to resist. 
Damage due to creep may be prevented by omitting expansion 
bearings on abutments. The construction of single span concrete 
bridges with two fixed bearings has been used for years by the 
Wisconsin Highway Commission for span lengths up to 45 feet. 
None of these bridges showed signs of creep. 


43 


Preventing 
Creep with 
Fixed 


Bearings 


Suggested 
Practice in 
Bearing 
Layout 


FIG. 51 


Similar methods of prevent- 
ing creep are used by the Bureau 
of Bridges in Ohio. Here two 
fixed bearings are used for slab 
decks with span lengths up to 
25 feet, and another method 
applying to longer span lengths 
has recently been adopted. The 
latter construction is indicated 
in Fig. 51* which shows a ver- 
tical section taken in front of 
the expansion bearing on the 
bridge seat. The sketch shows 
how the center part of the bridge 
seat is raised so that it forms a 
block, which acts as a key be- 
tween the central beams. The 


: > FIG. 50 Extruded joint filler indicates 
deck may move longitudinally, creep at the expansion end of a skew 


but lateral creep is prevented. bridge. Indications are that further creep 


This construction has been in will become destructive. 


use for a short time only but should give satisfactory results. It 
seems to be a highly desirable detail for use at all expansion bearings 
in skew bridges or bridges on curves. 

In view of the discussion in this section, as well as in preceding 
sections, the following rules appear to warrant considerable atten- 
tion: 

1. In single-span layouts, use two fixed bearings on the abut- 
ments when the span length does not exceed 45 feet. 

2. In two-span layouts, use fixed bearings on the abutments 
and expansion bearings on the pier. 


’ Plate of Lead orZinc/ Block on Bridge seat to prevent creép 


FIG. 51 Vertical section through deck shows expansion bearing in which creep is 
counteracted by raising the central portion of the bridge seat. 


*Not drawn to scale. 


44 


3. In three-span layouts, use fixed bearings on the abutments, 
two fixed bearings on one pier, and two expansion bearings 
on the other pier. 

4. In four-span layouts, use fixed bearings on the abutments 
and on the center pier; use expansion bearings on the other 
two piers. 

All expansion bearings in skew bridges or in bridges on curves 
should have the block between girders indicated in Fig. 51. 


c 


FIG. 52 Three arrangements of girders bearing on piers in a skew bridge. The pier 
width is often determined by the position of the bearings as indicated in type a. 
The width may be reduced considerably by use of the layouts in types b and c. 


FIGS. 52 and 53 


Valuable space may be wasted on piers supporting skew bridges 
when the bearings are arranged as indicated at a in Fig. 52. ‘This 
arrangement is often adopted for the purpose of obtaining straight 
deck joints. A narrower pier seat—and a more economical pier and 
bridge construction—may be obtained by placing the bearings much 
closer together as indicated at 6 and c in Fig. 52. It has been sug- 
gested that the deck joint be kept straight by means of a construc- 
tion as indicated at 0 in Figs. 52 and 53. Some bridge designers 
use a saw-toothed joint as indicated at c in these two illustrations. 


Rosdway ‘surface 


hes 


_ Roadway surface. 


Joint fill er: Fos 


“ Top of pier. of ~ : : : \ 


FIG. 53 Details suggested for jointing at piers in skew bridges. Type b has a straight 
deck joint, while the joint in the deck is saw-toothed in type c. 


45 


Frequent 
Maintenance 


Reducing 
Settlement 


When a skew slab as shown in Fig. 46 is loaded and deflects, 
the deck deformation will tend to raise the acute corner of the 
deck. Cracks of the type sketched in Fig. 46 may then develop. 
It is therefore advisable to provide suitable reinforcing bars in the 
top of the slab at its acute angle and preferably parallel to the long 
diagonal of the slab. 


APPROACH SETTLEMENT 


Maintenance work most frequently performed at bridges soon 
after completion is the raising of approach slabs that have settled. 
The cause of the settlement is to be found in the behavior of the 
backfill. 

The backfill behind the abutment is usually of materials such 
as clay, sand or earth. It is placed in layers but the use of water 
in the backfilling operation is usually prohibited since the abut- 
ments are rarely designed for the added hydraulic pressure. This 
type of backfill may settle considerably, and it is therefore best to 
leave a gap in the pavement on the approaches for some time. 
Such gaps are objectionable, and the approaches are usually paved 
shortly after the bridge is completed. The result is that the approach 
slab settles with the fill and cracks. 


‘ So BackAll 
Excavation line Fe. 
a 


FIG. 54 Two methods used in building approach slabs. The slab in type a is self- 
supporting and will not settle with the backfill. The slab in type b does settle with 
the fill, but provisions may be made for jacking up the slab again. 


Abutment 
Abutment 


FIG. 54 


The objectionable features accompanying settlement on ap- 
proaches may be eliminated in some instances. When conditions 
are favorable, it is advisable that the volume of excavation behind 
the abutment be kept as small as possible. In other words, the 
excavation line shown at a in Fig. 54 should be made as steep as 
the type of soil will permit. In addition, it is well to specify for 
backfill the use of coarse materials, such as stone or gravel. When 
this type of backfill is too expensive, ordinary earth backfill may 
be chosen. If so, it is advisable to proportion the approach slab 


46 


so that it can safely span from the pavement ledge on the abutment 
to the undisturbed soil behind the backfill. The approach slab 
will then remain at its original level when the backfill settles below it. 

Where the top of the undisturbed soil is as indicated at 6 in 
Fig. 54, the approach slab is usually built in sections. Roughness 
at transverse joints in the riding surface may be avoided by 
the use of short dowels extending across all joints, including the 
joint at the abutment ledge. If the slab should settle with the back- 
fill, it is usually raised to its original grade by means of the mud- 
pump operation. It may be well to anticipate this operation when 
the slab is built. Some designers, therefore, specify that holes be 
left in the slab properly arranged for future use as indicated at D 
in Fig. 54. Such holes may be about 2% inches in diameter and 
spaced about 5 feet apart in both directions. They should be filled 
tightly with mastic to protect the edges and make the holes water- 
tight. 

* oe x 


A digest of the observations made in the field has been presented 
with special attention given to those details that can be improved. 
The details that are being used universally with consistently good 
results have been omitted because they are so generally understood 
and require no discussion. 

Field observations have led to the conclusion that troublesome 
effects developed under the most adverse conditions only, although 
_the underlying causes of potential damage often exist. Despite the 
relative infrequency of troublesome cases, it is advisable to take 
proper precautions under all similar conditions. Cause, effect and 
precaution therefore have been given equal attention in the dis- 
cussion. It is hoped that these studies will stimulate further effort 
toward perfection of structural details in concrete bridges to keep 
abreast of the advancement in concrete quality. 


PeeeiveaA De CRM ENT ASSOCIATION 


eo WEST GRAND’ AVENUE ° CHIEGAGO T0meLULs 


Typical 
Approach 
Slab Practice 


Concluding 
Remarks 


Wiss 
' 


PRINTED IN_ U.S.A. 4 


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Hatetetete Tek Poteten seleleres 


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‘ 


financing 
water 


and 


sewage 
works 


FRONT COVER 


Water Works plant at Columbia, 
Miss. This attractive architectural 
concrete building, built in 1949, 
has an area on the roof for par- 
ties, dances and picnics. Engi- 
neers and architects: Mallett & 


Associates, Inc., Jackson, Miss. 


financing 
water 


and 
sewage 
works 


PORTLAND CEMENT ASSOCIATION 
33 West Grand Avenue ¢ Chicago 10, Illinois 


contents 


Introduction eee 
Financitig vy seats ee eee 
General Principles ......2.55. 900" 
Methods’. 12:12 at eae en tte 


General Obligation Bondsaanoe 
Special Assessment Bonds...... 
Revenue Dondsan sate ats 
Rate Structures, 2) .05.25 
Required Annual Revenues..... 
PresenusPracticesan ae 
Water ates sana eee 
Sewace Rates) sieves! see 
Recommended Procedures...... 
Water Rates.) 
Sewage Rates micas oo et eene 
Enforcement of Charges......... 


Publicity and Public Relations... . 


introduction 


Nile communities are confronted with the necessity of pro- 
viding adequate water and sewage facilities. Even though 
the urgency of these needs is recognized, there remains the 
problem of selecting a method of financing that will meet with 
public approval. 

Various methods of financing water and sewage projects are 
discussed in this booklet as a guide to municipal officials in 
adopting a plan that will best serve the interests of their com- 
munities. Also included is information on the principles of estab- 
lishing fair and equitable rate structures for water and sewage 
service charges as well as an outline for educational campaigns 
to obtain public support for such improvements. 

The health and welfare of every community and of the coun- 
try as a whole depend on a safe and adequate supply of water. 
Of equal importance is the satisfactory disposal of all industrial 
or domestic waste water, for water once used is re-used by the 
next city or industry downstream. The necessity of providing 
this dual service for rapidly expanding urban centers creates 
many difficult problems for public officials. 

It has been estimated that our population, which is more 
than 160 million today, will reach 200 million by 1975 and that 
industrial production will double in the next 25 years. This 
means an enormous increase in the demand for water. New 
uses—air conditioning, garbage disposal units, automatic dish- 
washers and laundry machines—will also greatly increase con- 


Fig. 1 

180 

160 

140 

120 
“” 
£ 
& 

: 100 
& 
c 
¥ 

3 80 
>, 
a 
° 
a. 

60 

40 

20 

0) 


sumption of water in homes and business establishments. (See 
Fig. 1.) And, in the not-too-distant future, the developments 
in nuclear power may pose some real problems in the use, treat- 
ment and disposal of contaminated water. 

The U.S. Department of Commerce has published reports on 
an exhaustive study of public water and sewage works needs. 
The value of facilities in service in 1954 was estimated at $42 
billion, of which $23 billion is in the field of water supply and 
$19 billion in sewerage. To meet present demands and to serve 
future needs of a growing population, it is estimated that $25 
billion worth of construction should be undertaken during the 
next 10 years. (See Fig. 2.) This would mean an average annual 
expenditure of $214 billion, more than twice the current outlay. 


ESTIMATED GROWTH IN COMMUNITY POPULATION 
AND WATER USE 


AVERAGE DAILY PER CAPITA WATER USE 


TOTAL COMMUNITY 


160 


100 


Per capita water use in gallons per day 


POPULATION 
80 
POPULATION SERVED BY 
PUBLIC WATER SUPPLIES 
60 
40 
20 
(0) 
1910 1915 1920: 1925 1930 1935 1940 1945 1950 1955551960 
Year Source: U.S. Department of Commerce. 


Fig. 2 


Needed construction in billions of dollars 


Financing such a large construction program presents some 
difficulties. Property taxes are at a high level and there is always 
opposition to any increase in the tax rate. This has given rise 
to other methods of financing, such as the ‘“‘pay as you use” or 
service charge method, otherwise known as revenue financing. 
This method for financing all or part of a water and sewage 
works has increased in popularity during the past decade. Reve- 
nue bonds are regarded by purchasers as good investments. 

It is essential that sound methods of financing be selected 
if the urgently needed sanitation facilities are to be provided 
within the desired 10-year period. To delay them will adversely 
affect our national economy, destroy many recreational areas, 
and, of more importance, endanger public health. 


NEEDED CONSTRUCTION DURING NEXT 10 YEARS 


SEWAGE WORKS 


—;—— 


Amount needed 


for growth 
WATER WORKS | 
Amount To offset 
needed for obsolescence 
growth 
To offset 


obsolescence 


Present 
i, deficiencies 
Yj 


New construction— 
Present 


deficiencies Yf 
in planning stage 


Source: Report, U.S. Departments of Commerce and Labor, 1955. 


7 


financing 


Since local units of government—counties, districts or authori- 
ties—derive their powers from the states, specific statutes and 
the state constitutions control the extent to which local govern- 
ments can finance needed projects. Existing legislation should 
be carefully examined to see that there are no defects in the 
present statutes that might act as a deterrent to financing. 
Adequate enabling legislation must be provided if it does not 
exist. Special bond counsel with wide experience should be em- 
ployed by the governmental unit contemplating extensive water 
and sewage improvements. Special counsel, working in close 
cooperation with local attorneys, can make a thorough study 
well in advance of a definite program. 

It is also desirable to employ a financial consultant to furnish 
the governmental unit with an impartial opinion and advice on 
market conditions for any contemplated bond issue. 

The covenants to be made in the bond instrument must be 
carefully considered well in advance. It must be determined 
beyond question in the early deliberations of the public bodies 
that the local officials have the necessary authority to make the 
covenants. Legal and financial counsel can be of special service 
on these matters. Bond counsel will be able to check the legality 
of the proceedings of the public body as they progress, thus pre- 
venting errors that might affect the validity of the bonds and 
delay construction of the needed improvement. The financial 
consultant will be in a position to advise on matters of rates, 
timing and marketability. 


general principles 


The ever-present problem for the municipality—as for the in- 
dividual—is one of paying for a desired service or improvement. 
At the risk of oversimplification, a formula for testing the bor- 
rowing power is described here that can be used as a guide when 
a financial plan for water and sewage facility improvements is 
being considered. The basic elements involved, regarded as fac- 
tors of the formula, can be expressed algebraically as 
CG, +C,4+ C; = C,, 

where C, = Capital; 

Ca-=" Capacity: 

CG = Character; 

C, = Credit, or the trustworthiness of the promise to 

repay borrowed funds. 

The value assigned to Capital (C,) will depend on value of 
property and equipment and other resources. 

The value given Capacity (C2) is often considered in conjunc- 
tion with Character (C3). This is particularly true of a munici- 
pality where the earning capacity of its utility services may be 
substantially influenced by the character of the community. 
The earning power, existing or potential, is the measure of a 
municipality’s capacity to pay for improvements over a given 
period. The essential nature of water supply and waste-water 
disposal assures a steady income from reasonable rates, and 
modern methods of billing and collection with prompt follow-up 
reduce delinquencies to a minimum. 

The character of a community is apparent from a statistical 
analysis. Its population growth, types of industry, volume of 
trade, home ownership, and assessed property valuation will 
all be important factors in the test for credit. 


methods 


Most communities cannot finance extensive public improve- 
ments on a cash basis. Therefore, financing all or a portion of 


the improvement by borrowing is common. Borrowing may be 
accomplished by the issuance of (1) general obligation bonds, 
(2) special assessment bonds, (3) revenue bonds, or by a com- 
bination of these. 

Whichever form of financing is used, the municipality will 
benefit by preparation of a complete financial analysis. Advance 
knowledge of the specific information required will give the local 
unit of government sufficient time to collect and tabulate data 
for use when needed. The information and figures should be as 
accurate and up to date as possible. If this is done a clear pres- 
entation of the financial position and the Capital (C,), Capacity 
(C.) and Character (C3) of the municipal unit can be made. To 
simplify analysis and interpretation the information should be 
presented in a uniform pattern as briefly as adequacy permits. 
The Municipal Securities Committee of the Investment Bankers 
Association of America has prepared convenient report forms for 
this purpose, which are reproduced in the Appendix of this 
booklet with the Association’s permission. 


general obligation bonds 


The first and best-known method is based on governmental 
credit and the taxing power of the community. To secure this 
the full faith and credit of the governmental unit, backed by 
its taxing power, is pledged; the amount borrowed becomes a 
general obligation and must be paid without regard to any spe- 
cific fund. General obligation (G.O.) bonds are not considered 
“risk”” capital and generally carry a low interest rate. They 
usually require a referendum and may be rejected unless there 
has been a good educational campaign on the merits of the 
project for which they are intended. 


special assessment bonds 


The laws governing special assessment bonds vary from state 
to state. The bonds are generally payable from assessments 
based on benefits to private property and become a lien on the 
property benefited. In some instances a part of the cost may 


be assumed by the municipality as a public benefit and paid 
for from general or ad valorem taxes. 

Although not used as frequently now as formerly, special 
assessment bonds are sometimes used in combination with gen- 
eral obligation or revenue bonds. Such a financing method has 
considerable merit because it permits the cost to be spread on 
a more equitable basis among users, property benefit and the 
general public. 


revenue bonds 


When a project under consideration is one that provides a 
direct service such as water supply and waste-water disposal, 
it can frequently be shown that the application of a service 
charge can develop an earning capacity enabling the improve- 
ment to be financed, built and operated as a “‘self-liquidating”’ 
project. Financing through the sale of bonds on which principal 
and interest payments are solely from the income derived from 
operation of the facility is referred to as revenue financing. 
Since the taxing power of the governmental unit is not used, 
revenue bonds do not constitute a municipal debt within the 
meaning of constitutional or statutory limitations. 

However, revenue bond financing should not be regarded as 
a device to overcome constitutional or statutory debt restric- 
tions. This method should be based on the merits of the project 
and be able to withstand a critical financial analysis. 

There is a definite advantage in using revenue financing for 
water supply and sewage disposal projects because it places 
these essential services on a businesslike basis. The service that 
these projects provide is ideally suited to revenue financing be- 
cause a moderate periodic charge can be made for it. 

To meet the requirements for sound financing the munici- 
pality may plan a financial program that uses both revenue and 
general obligation bonds. With this method, interest rates are 
usually lower than when the project is financed solely by the 
sale of revenue bonds. 


rate structures 


required annual 
revenues 


Closely related to the revenue-bond method of financing water 
and sewage works projects is the problem of establishing fair 
rates. This is a matter of prime importance because the rate 
structure will be scrutinized critically by the citizens who use 
the service as well as by the purchaser or underwriter of the 
bond issue, but until recently there was little authoritative in- 
formation conveniently available. 

There has now been made public a joint report of the Ameri- 
can Society of Civil Engineers, the Section of Municipal Law 
of the American Bar Association, and six other participating 
national organizations*—‘‘Fundamental Considerations in 
Rates and Rate Structures for Water and Sewage Works,”’ Ohio 
State Law Journal, Spring 1951. This has been cited by the 
courts as authority when the questions of rates and enforce- 
ment of charges have been issues. Much of the following ma- 
terial has been abstracted from this report. 

Municipal and other publicly owned water and sewage works 
are usually not operated for profit, but are generally organized 
to serve the public on a cost basis, the theory being that the 


*American Water Works Association, National Association of Railroad and 
Utilities Commissioners, Municipal Finance Officers Association, Federation 
of Sewage Works Associations, American Public Works Association, and In- 


vestment Bankers Association of America. 


required revenue is the amount necessary to meet the cash out- 
lays as they fall due. If the debt is due at one time, a fund must 
be accumulated to pay off the debt at maturity. If the debt is 
payable in installments, the money must be collected to dis- 
charge the installments as they come due. 

The total annual revenue required covers debt service (prin- 
cipal and interest), maintenance and operation, depreciation 
reserve for replacement of equipment, and other contingencies. 


present practices 


There is, at the present time, no uniform practice in determin- 
ing rates and rate structures. In the past, scant consideration 
has been given to fundamental principles, and too often it has 
been a matter of adopting any plan that would produce suf- 
ficient revenue with the fewest complaints. 


water rates 


Existing water rates fall into two large categories: (1) the sale 
of a commodity and (2) the furnishing of fire protection. Com- 
modity rates are those charged to the customer to cover the 
cost of producing and delivering water to him. The following 
rate bases are in common use. 


1. Flat rates for unmetered customers: This rate class is 
used in both large and small cities. It is popular where 
water is unusually plentiful and can be provided at 
relatively low cost. Some of our largest cities still have 
flat rates for all except large users, a carry-over from 
their early practices. 

Flat rates are usually based on the number and types 
of installed fixtures, the number of rooms, the number 
of occupants, or the type of occupancy. They are at 
best only estimates of the average use of water. 


2. Rates based on property valuation: This class of rate, 
based on either the value of the property for taxing 


14 


5. 


purposes or on its value for rental purposes, is used in 
Canada and a few cities of the United States. 


Uniform metered rates: A single-rate charge for water 
came into use after the introduction of water meters. 
A customer using 100,000 gal. per month pays exactly 
10 times what a customer using 10,000 gal. per month 
pays. It is reported that slightly more than 4 per cent. 
of cities of 10,000 population or over use uniform rates. 


Sliding scale metered rates: Studies by water-works man- 
agements showed that the cost of service to different 
classes of customers was not the same. A fair distribu- 
tion of cost entitles a customer who uses a large amount 
of water to a lower rate for the increased amount than 
that charged a customer who uses a small amount of 
water. To distribute costs fairly, a sliding scale rate 
schedule, called a “‘block”’ or “‘step,”’ was devised. 

The following example illustrates such a rate schedule: 


Block or step in gallons Rate in cents per 
per month 1,000 gal. 
First 25,000 5 3575 o656010:0.syerste 6 0:8 10 o:0,0 sie 0) sleeves) st ef eneheneeieeae 20.0 
Next 225,000 ooo 5566.5 cies voiere.s ave 5 evere oie ogee seit revere 15.0 
Over250, 000 aie 5 si. io ieceirete rere seiatel os sore c's tsrotsic\ sic etote eens 10.0 


This type of rate schedule, if it is properly designed, 
should be based on the cost of supplying water to each 
class of users. It attempts to divide the cost of water 
service into three elements: 


a. The capacity, or readiness-to-serve, cost. 

b. The commodity cost or the cost of producing 
and delivering the water. 

c. The customer cost or the cost of meter reading, 
billing, collecting and accounting. 


Additional provisions in rate schedules: A minimum rate, 
with or without a service charge, is usually incorporated 
into both uniform and sliding scale rates. These sched- 
ules stipulate a minimum charge for the collection 
period. For both uniform and sliding scale rates this 
charge usually covers some quantity of water—for ex- 
ample, up to 3,000 gal. per month—and may or may 
not include a service charge for the meter. If a meter 
charge is included, it varies with the size of the meter. 


Miscellaneous charges incorporated into some rate schedules 
include such items as “‘construction water,” “sprinkling water’ 
and “‘irrigation water.’’ Since in each of these cases the service 
is limited to the season of the year or to geographic location, 
the charge is too variable to report except as a matter of gen- 
eral interest. 

Other charges, sometimes incorporated into the published 
rate schedules, include a fee for making a water service tap, for 
the service connection and for setting the meter. 

Charges for fire protection do not follow any uniform prac- 
tice. The cost of such protection varies with the size of the water 
works and the community. 

The collection of income for public fire protection is achieved 
through charges against the municipality or other governmental 
agency or through charges against the owners of private prop- 
erty. In the former case the charge may be either an annual 
lump sum or a charge per hydrant and per linear foot of main. 
The charge thus becomes a source of revenue from general taxes 
that is often partly offset if ‘‘free water’’ is furnished to the 
governmental agency for public buildings, parks, playgrounds 
or similar services for which no payment is made. 


sewage rates 


Sewers have been used for many years, but the operation of 
sewage treatment works is a relatively new municipal function. 
It has created a financial problem since the usual sources of 
municipal revenues have been largely pre-empted for other uses. 
This has resulted in a search for additional revenues and has 
stimulated interest in special charges for the use and benefit of 
sewage works. These sewage service charges have generally not 
been established on an equitable basis. 

An examination of current practices indicates that among 
municipalities charging for sewage service there are wide varia- 
tions in the extent to which such revenues are relied on to meet 
the cost of the sewage works. Some use such revenues to finance 
the construction of new sewer systems or new treatment works, 
others to pay the debts on existing sewage works, and still 
others to pay only the current operating and maintenance costs 


15 


of the sewers or the treatment works, or both. The wide range 

in the amount of revenue raised and the bases for collection 

make it appear that few rate structures have been scientifically 

designed. It seems that all efforts have been made to raise some 

definite amount of revenue in the easiest manner, rather than 

to fix the rates on a fair basis in true relation to the cost of pro- 

viding for the use and benefit of the works. 

The design of rates and rate schedules for sewage works has 

included several factors: 

1. Financing method used in construction. 

2. Sewage characteristics. 

3. Quantity of sewage. 

4. Degree of treatment. 

5. Effect of the charges on the various classes of individuals 
who pay them. 

Four bases for charges in common use are: 


1 


Metered water charges: A sewage charge based on 
metered water use represents the most accurate meas- 
ure of the relative use of the sewage works, generally 
resulting in the fairest distribution of charges. How- 
ever, Inaccuracies and inequalities are introduced when 
all of the water used is not discharged into the sanitary 
sewers, as, for example, where some is used for lawn 
sprinkling. The method is also open to the objection 
that it does not take into account the benefit to unde- 
veloped property. Consequently, adjustments for both 
users and properties are required if charges are to be 
made in proportion to use and benefits. 

Rate schedules of this type usually include a mini- 
mum annual charge and are generally on a sliding scale, 
with a lower charge for greater quantities; maximum 
charges in the first block are approximately 50 per cent 
more than the minimum charges of the last block. 


Combined sewage and water charges: Acombined sewage 
and water charge is not commonly used. This plan pro- 
vides for only one charge to yield both water and sew- 
age revenues. The plan has no justification except sim- 
plification of billing procedure because it does not reflect 
true use charge for either water or sewage service. 


3. Charges based on metered water and strength of sewage: 
A charge based on metered water and the strength or 
characteristics of the sewage is more exact than one 
based on the quantity of water or sewage, particularly 
if the works include sewage treatment. The charge, 
therefore, should take into account the type of treat- 
ment and the proportion of the cost due to the quantity 
and characteristics of the sewage. Such a method need 
not be applied to all sewage sources, but only where 
the sewage strength or volume is especially high. 


4. Fixed percentage of water bill: Sewage charges estab- 
lished as a fixed percentage of the water bills are perhaps 
the most common. The billing procedure is simpler and 
cheaper than when a separate rate structure is adopted, 
and the plan includes all users whether the water service 
is metered or not. However, such a method carries over 
any unfairness in water-rate schedules. The range is 
from a minimum of 10 per cent to a maximum of 200 
per cent with a normal range between 20 and 50 per 
cent, but these percentage figures have little meaning 
unless the water-rate structure is also known. 


recommended procedures 


A basic principle stated in the joint committee report, ““Funda- 
mental Considerations in Rates and Rate Structures for Water 
and Sewage Works,”’ is the following: 

“The needed total annual revenue of a water or sewage 
works shall be contributed by users and non-users (or by 
users and properties) for whose use, need and benefit the 
facilities of the works are provided approximately in propor- 
tion to the cost of providing the use and the benefit of the 
works.” 

The application of this principle to the determination of fair 
rates and rate structures for any particular situation will in- 
volve, in the first instance, the determination of the share to be 


borne by users and non-users, and in the second instance, an 
allocation among different classes of users and non-users. 

Dual rate structures will usually be required, one for users and 
the other for non-users. The rate schedule for that part of the 
needed total annual revenue to be contributed by users will 
ordinarily fall into usual well-known classifications. Rate sched- 
ules for that part of the needed total annual revenue to be 
contributed by non-users are not generally well known, al- 
though such rate schedules have been used for some years by 
the Buffalo Sewer Authority for sewage works and by the 
Washington Suburban Sanitary Commission for both water and 
sewage works. 


water rates 


The initial step in determining the proper rate structure for a 
water works, which raises its required annual revenue entirely 
from users, or for the use portion where both users and non-users 
are charged, is the allocation of the total cost of service or the 
use share between two major types of uses—public fire protec- 
tion and general service. This requires the segregation and 
assignment to each class of the service costs directly attributable 
to that class, and the division of the remaining joint costs on 
some fair basis. A rate structure must then be created that will 
return the required annual revenues in the proper proportion 
from each class and, in the case of general service—that is, uses 
other than public fire protection—in the proper proportion from 
the several classes of users. 

A detailed analysis of a project with fair allocation of costs 
based on the actual cost of providing the service will enable 
local officials to select a reasonable division for combined financ- 
ing with general obligation bonds and revenue bonds. 

A typical analysis to determine a fair rate structure for a 
water-works project is included in “‘Determination of Fair Sew- 
age Service Charges for Industrial Wastes—A Discussion,”’ by 
Thomas M. Niles, which appeared in Sewage and Industrial 
Wastes, Vol. 24, No. 2, February 1952, pages 215-221.* 


*Reprints of this article are available on request from the Portland Cement 
Association. Distribution is made only in the United States and Canada. 


sewage rates 


The first step in determining the proper rate structure for sew- 
age service charges is to prepare a descriptive list of the various 
elements of each major part of the works—for example, collect- 
ing sewers, intercepting sewers, pumping station and various 
component parts of the treatment plant. The second step is to 
determine annual fixed and operating costs for all elements 
listed. The third step is to apportion these amounts, on an 
equitable basis, between users and property. The fourth step is 
to subdivide the users’ share on the basis of quantity of sewage, 
suspended solids and strength of sewage (BOD). If the annual 
fixed and operating costs are known, it 1s then possible to allo- 
cate an equitable charge based on volume, suspended solids and 
strength of sewage both to the users and to property. 

A typical example of a cost analysis for determining fair 
sewage service charges can be found in “Determination of Fair 
Sewage Service Charges for Industrial Wastes,’ by George J. 
Schroepfer, printed in Sewage and Industrial Wastes, Vol. 23, 
No. 12, December 1951, pages 1493-1515. * 

From a practical standpoint it is desirable to show water and 
sewage service charges on the same bill but as separate items. 
To avoid a heavy burden on the accounting and billing depart- 
ments, the billing periods may be staggered alphabetically, or 
by area or district division of accounts. 


enforcement of charges 


Adequate power to enforce the charges is especially important 
when revenue financing is used. The monthly charges for the 
domestic user are relatively small but there is always a small 
percentage of the total accounts that are difficult to collect. 
Follow-up notices are necessary in such cases. Postal card 
notices and reminders of the overdue account have proved effec- 
tive in collecting bills when the amount in arrears is small and 


*Reprints of this article are available on request from the Portland Cement 
Association. Distribution is made only in the United States and Canada. 


the overdue date fairly recent. For delinquent accounts of longer 
duration more positive means of collection are necessary. 

The most drastic is to shut off the water. For the purpose of 
collecting delinquent water bills this sanction has been generally 
available and accepted. The use of the water shut-off method to 
enforce payment of the service charge for sewage works was not 
so generally accepted until favorable court decisions upheld the 
right of a municipality to invoke this sanction. A notable case 
was decided by the Supreme Court of Florida in 1946, on the 
theory that the two services, water supply and sewage disposal, 
were interdependent and could be considered as one (State vs. 
City of Miami 157 Fla. 726). A Pennsylvania law requires a 
water utility to shut off service to a customer who is more than 
30 days in arrears on sewage service charges, when requested 
to do so by a local unit of government. 

To encourage prompt payment of water and sewage bills 
many municipalities have adopted the discount method. This is 
generally considered a fair and practical method when related 
to the savings in cost of collection. As in other phases of admin- 
istration the enforcement of payment involves good public rela- 
tions. The positive enforcement of charges can be accomplished 
and the good will of customers can be retained if the methods 
are made known and strictly followed. Any leniency should be 
provided within the framework of the method and not as an 
exception to the general practice. 


publicity 
and 
public 

relations 


When any public utility improvement program is being planned 
it is highly desirable to prepare an outline for an educational 
campaign well in advance. State health departments and water- 
pollution-control agencies are always willing to assist munici- 
palities in this preparation. A suggested outline covering the 
principal steps in the campaign follows: 


A. Organization 
1. Foim a steering committee 
2. Establish headquarters 
3. Select staff 
a. Publicity director 
b. Volunteers for secretarial and other duties 


B. Collecting facts 

1. On need 
a. Engineer’s report 
b. Public health requirements 

2. On feasibility 
a. Financial consultant’s report —methods of 

finance 

3. On legislative needs 
a. Present provisions 
b. Recommended changes 
c. Power of municipality to act promptly 


2 


C. Publicity 
1. Newspapers 
a. Articles 
b. Letter of endorsement by prominent citizen 
c. Advertisements 
2. Mailings 
a. Preparation of material 
b. Distribution 
3. Public meetings, radio and television 
a. Talks by citizens, engineers, attorneys, clergy 
4. Displays 
a. Posters 
b. Models 
c. Pictures 
D. Cooperation of local organizations 
1. Chambers of Commerce 
2. Service or social clubs 
3. Professional societies 
4, Izaak Walton League 


E. Individual contact 


1. Door to door 
2. Telephone calls 


If there are controversial questions, they should be resolved 
before the project is financed. This may not be possible in some 
cases and public support then becomes the determining factor. 
When the campaign terminates with a referendum a strong 
closing statement should be made public that presents the facts 
and stresses the vital need for the proposed improvement. 

The huge construction program necessary to meet present 
demands for needed water-supply and sewage-disposal facili- 
ties will be substantially aided by intelligent educational cam- 
paigns. Data concisely presented by a few progressive munici- 
palities would help to set the pattern for a more uniform 
presentation of engineering, legal and financial reports. 

After the project has been financed and built, periodic reports 
should be prepared and distributed to customers and banking 
groups. In addition to a financial statement, such reports should 
contain items and information of interest, well illustrated with 
pictures and charts. Reports that show the businesslike opera- 


22 


tions of the municipal corporation will establish a valuable 
credit barometer for future improvements. 

The Portland Cement Association through its several dis- 
trict offices is ready to cooperate with public officials in the 
development of a sound program for constructing water-supply 
and sewage-disposal facilities and other public improvements. 


23 


appendix 


IBA Revenue Bond Report — Form No. 2 Sewer 


Condensed Report of Revenue and Expenditures of the 


(Insert name of issuing political body) 


FOR THE PERIODS SHOWN 


Fiscal Year Same period Same per: 
ended 1 year ago 2 years 4) 
1. Operating Revenue $e Fe 
2. Nonoperating Revenue ———————— ————ee 
3. Total Groas Revenue } ee ye 
4. Expenditures for Operation & Maintenance (incl. payments 
for Employees Retirement & Disability Fund) Se EEE et 
5. Other charges, if any, against Gross Revenue le Eee | 
6. Net Income available for debt service saetne Samet a ae 
7. Interest paid on bonded debt SE eee _—_——____ iB 
8. Principal paid on bonded debt Ee —— 
(a) Matured ————— Poe eS — 
(b) Called a ae ee ae 
9. Other charges against Net Income (specify various funds) * 
(a) ee ee ee ae ————— a 
(b) EE ee a ee 
(CC) ee ae pee eS WS — 
(d) ee ———E—— ae _— 
10. Amount available for retirement of débt by call SS —————— fener se see —_—__ =F 
11. Surplus (state to what uses surplus has been or may be put) 
12. Total amount of bonds issued (original & subsequent) 
13. Bonded debt at end of period (also show below) 
(a) Bank loans at end of period 
(b) Other unfunded debt at end of period 
14. Principal & Interest on bonded debt next fiscal year 
15. Maximum Principal & Interest requirement on present debt 
in any future fiscal year 
16. Total amount accumulated in reserve funds** 
(name & amount) 
17. Present book value of plant and equipment after depreciation 
18. Estimated average daily water supply (in gallons) 
19. Average daily water consumption (in gallons) — fj 
20. Water storage capacity (in gallons) —__ 
21. Number of customers at end of period—Residential — 
Commercial ae 
Industrial —_ 
All Others SS —————— —_ =e 
22. Gallons water consumed per customer—Residential __ =a 
Commercial — | 
Industrial — | 
All Others — a 
*What method of depreciation is used? = 
*What disposition is made of revenue in these funds? — 


**How are reserve funds invested? 


(See reverse side) 
Investment Bankers Association ef America 


24 


Page 2 of Form No. 2 Sewer 


Latest Balance Sheet 


YN ois a a ae a oA eo 8h cc 
(Insert or attach copy) 


Nol 


Are there any contingent liabilities not shown in the balance sheet? Yes 
If “Yes”, explain. 


Name and address of auditor preparing the annual audit. 


Is the auditor an independent auditor? Yes No . 
Is sewer service charge based on amount of water metered? Yes 


. If not what is the base? 


No 


No 


Does the sewer charge appear on water bill? Yes 


May water and sewer charges be paid separately? Yes No . If “Yes”, explain 


If sewer charge is not paid, does it become a lien on real property? 
May past due water bills become a lien on the property? - 
What is the source of water supply? 


Does the system contain a sewage treatment plant? 


Other Pertinent Data or Comments 


Signed 


Official Title 


Report on Finances 


MUNICIPALT Ry ee eee ere eee S UAC Fen) 17, 
FORM OF GOVERNMENT (Commission, Mayor-Council, Manager, etc.) 


PROPERTY VALUATION 
Current Year, 19__ Previous Year, 1Q2.— 
Actual or Full Valuation See $ 


Assessed or Taxable Valuation $e $ 
Assessed Valuation is legally. % of Actual Valuation. 
U. S. Census 1930__________ State Census____________(give date) 19___ Present Estimate—____—_ 
Has this municipality ever defaulted on debt obligations? 
If so, give full particulars in a separate statement. 
BONDED DEBT 
(aS of ee, 


) 


Purpose of Issue Outstanding Sinking Funds 


General (include all purposes not listed below) 
Special Assessments, payable also from general taxation 


Utility Debt, payable also from general taxation: 
(a) Water 


(b) Light and Power 
(c) Other (specify) 


TOTAL GENERAL OBLIGATION BONDS 
Special Assessments only 
Utility Revenue only 
(a) Water 
(b) Light and Power 
(c) Other (specify) 
TOTAL OTHER THAN GENERAL 
OBLIGATION BONDS 


List below amount and maturities of bonds (included above) issued within last two years for the following purposes : 


(a) Relief Se ee Maturities 
(b) Funding be ee eS ee Maturities 
(tRetunding Fo Maturities 


If refunding bonds were issued, were they sold at public sale or exchanged for maturing bonds? 


If exchanged, how did interest rate compare with bonds refunded 2 

Total General Obligation Bonds year ago this date $____________2 years ago this date $ 
Bonds now authorized but not issued: Purpose —________ Amount $ 

Are utility bonds fully supported by earnings of the property ? 

If not, what proportion of general taxes is necessary ? $ 

Legal debt limit of this municipality 


OVERLAPPING DEBT 


(That Part of Debt of School or Special Districts, Counties, etc., 
Payable by Taxes Levied in this Municipality ) 


Debt Gross Debt This Municipality's 
Name of Overlapping Entity Limit % Less Sinking Fund Share 


Copyright, 1934, Investment Bankers Association of America 


26 


Page 2 


CONDITION OF SINKING FUNDS 


Cash on hand or in bank et ne a Ee a 
United States Government securities peek! {eet foe eee 
Your own bonds 5 eee ee 
Bonds of your state $= 
Bonds of other states 
Bonds of other municipalities in your state 
Other municipals 
Other investments (specify nature) 

TOTAL 
AMOUNT OF TERM Bonps FoR WHICH SINKING Funps ARE REQUIRED 


PRINCIPAL REQUIREMENTS FOR NEXT FIVE YEARS 


Fiscal Year Beginning 


AUTHORIZED SOURCE OF PAYMENT 19__ 19__ 19S ome 1 

General Taxation ee ef | ee ee 

Special Assessments Only ee ee Ge Ge en ee 

Special Assessments and also General Taxation ee) ee, ee, SS, 

Utility Revenues Only ee eS ee, rn: eee 

BE aity Revenucs/and also’ General Taxation™ $= fgg 
UNFUNDED DEBT OUTSTANDING 


(aslo, =e TS ) 


R.F.C. Loans $ ee Sectired by. 
Tax Anticipation Notes Ss Due 
Delinquent Tax Notes $ Due 
Bond Anticipation Notes $ Due 


Bvatratits: $2 Bankgoansi$2— Judgments $. / 
Unpaid Bills 60 days past due $___ Miscellaneous $ 
eID Se te Secured shy. 


Soray UNrunDeD Dest $_—__________Year Ago $______ Ss? Yr, Ago $ 
COMPARATIVE STATEMENT OF OPERATING RECEIPTS and DISBURSEMENTS 
(Your Government Only—Do Not Include Municipally Operated Utilities) 
When does your fiscal year begin? 


Fiscal Year Beginning 


Cash Balance at beginning of year 
|) RECEIPTS: 


(a) Proceeds of bonds sold es ee ee a ee 
(b) Receipts from ad valorem taxes [eC ee hee ees 
(c) Receipts from other taxes $e ee ee eee 
(d) Receipts from other sources GP a as wh Nie a ee 
Total Receipts ee Se ee ee 
| EXPENDITURES: 
(a) Expenditures of bond proceeds a Ed 
t (b) Bond principal 5 eee ee Ce eS 
| (c) Bond interest le SE aad mest el SN 
| (d) Sinking Funds oo eee See eee 


$ 
(e) All other purposes ———— ae 
Total Expenditures ee 
a _—— 


Cash Balance at end of year 


eens 


Page 3 
TAX DATA 


Taxes for fiscal year beginning. 19.__are due___________19—_= 3 become aelmauers 


19 If payable in installments give particulars —.£§$@-—@£§$\————————————_ 
eee UCt—<~=~S 
Discounts for prepayment and when applied 2 $$—@$#-—$@$@AAA@@@$@O 
= t—<CSti‘“<‘<‘<C:;” 
Specific penalties for delingyeney $$ Aa Aa a i 
Explain in detail any modifications of penalties or penalty dates which have been made during last two years 
I 
<a tC Ct tttttt—S 


How are uncollected taxes handled? 
a. Included in next year’s budget ?___——__—_———— 


b. Turned over to other governing bodies and when 2? eee 


c. Sale of tax certificates and when ?___ 
d. Other. methods 


Has tax sale period been extended in last two years 2 EOE Ee 


Tf so, explain ————— 


TAX COLLECTION REPORT 


Fiscal Year 
Beginning Total Ad Valorem or General Uncollected Uncollected Uncollected 


Month______ Property Tax (omit special at End of Latest Available at Approx- 
imately Same 


Date 
Month___Day___Year__— Date Last Year 


Day—_ assessments and levies o Tax or Fiscal 
other taxing bodies) Year 
(Last three years) 


City eee oe 
800 = aaa 
Total general property or ad valorem tax for current year composed of : Sa —O————————e 
ny Eye 


eee 


TAX TITLE LIENS, TAX LIMITS, ETC. 


Accumulated total of uncollected taxes for fiscal years prior to those reported above Ee 
Total tax title liens owned by municipality (years 19 to 19____ inclusive) =a 
Are tax title liens included in uncollected tax totals above? How much? 9a 
How much?___________ Statutory on Constitutional =——————— 


Is there a tax rate limit? 
Does this apply to debt service™ 7 @$_$€$A a 


Do you levy taxes in excess of actual requirements to provide margin against delinquencies ?. 


—— 


If so, what ratio? 


Page ¢ 
SPECIAL ASSESSMENT COLLECTION REPORT 


Fiscal Year Uncollected at End Uncollected Latest Date Avail- 
Beginning of Year of Levy able Month__Day___Year__ 
(Last three years) 


Are special assessment bonds general obligations or only EOD ent Vater s\:eeeeae ee 


If former, is this by virtue of state law or city charter ee ee ee ee ees 
Are delinquent special assessments enforced in the same manner as tax hens? a ere 


If not, © 


BANK DEPOSITS 
(all your funds) 


FAMOUNt go as Of 
How are deposits secured 2 
What amount of funds, if any, in closed banks? 
(a) Operating Fund $_______________Secured?____———s How a a a ce i ee 
(b) Sinking Fund $ Secured? How ee ee ee a ee 


19___. In how many open banks? 


OTHER PERTINENT DATA 


SGI: ) See ee oe ea ee ee eee 


ee eee Official Title a 
3-34 


bibliography 


30 


“Revenue Bond Legislation,” Americé| 


Robinson, S. B., ‘Financing through Rey 
enue Bonds,” Report No. 107, Natior| 
al Institute of Municipal Law Officer 
730 Jackson Place N.W.., Washingto 
6, D.C., 1944. 


Wood, David, “Financing Municipal Pro) 
ects with Revenue Bonds.” Address ;/ 
meeting of Municipal Section, Amer 
can Bar Association, October 19, 194) 


Water Works Association Journal, Vii 
39, No. 10, October 1947, pages 102, 
1037; } 


Friel, Francis S., ‘‘Financing Sewal 
Works,” Sewage Works Journal, VI 
19, No. 3, 1947, page 379. 


Mitchell, Robie L., “Financing of Sew) 
Improvements,” Daily Bond | 
February 24, 1948. | 


Joyce, John J., and Nollett, Frank, ‘Sey 
Rental Financing in a Large am 
Small Community,” Sewage and | 
dustrial Wastes, Vol. 22, No. 9, S; 
tember 1950, pages 1103-1110. 


Tatlock, Myron W., “Sewage Servi 
Charge Practice,’ Sewage and Ina} 
trial Wastes, Vol. 22, No. 12, Dect} 
ber 1950, pages 1536-1542. 


Fundamental Considerations in Rates 

and Rate Structures for Water and 
Sewage Works,” Ohio State Law Jour- 
nal, Vol. 12, No. 2, Spring 1951. 


Imer, W. L., “Financing Water Works 
_Improvements,’’ American Water 
Works Association Journal, Vol. 43, 
- No. 4, April 1951, pages 313-321. 


inningham, John W., ‘Relationship of 

Water and Sewage Works Financing,” 
_ American Water Works Association 
_ Journal, Vol. 43, No. 11, November 
1951, pages 937-940. 


wroepfer, George J., ‘“Determination of 

Fair Sewage Service Charges for In- 
dustrial Wastes,” Sewage and Indus- 
| trial Wastes, Vol. 23, No. 12, Decem- 
_ ber 1951, pages 1493-1515. 


. 


es, Thomas M., ‘‘Determination of 
| Fair Sewage Service Charges for In- 
dustrial Wastes—A Discussion,” Sew- 
age and Industrial Wastes, Vol. 24, No. 
2, February 1952, pages 215-221. 


Wainwright, Townsend, “Municipal Fi- 
nancial Consultant Service,’ Ameri- 
can Water Works Association Journal, 
WVol44) No.2: February 1952, pages 
93-99. 


Smith, F. Burton, “Establishment of Rate 
Differentials Inside and Outside City 
Limits,’ American Water Works Asso- 
ciation Journal, Vol. 44, No. 2, Febru- 
ary 1952, pages 142-148. 


Sewage Service Charges in Cities over 5,000 
Population, Special Report No. 18, 
American Public Works Association, 
November 1953. 


‘Determination of Water Rate Schedules,”’ 
American Water Works Association 
Journal, Vol. 46, No. 3, March 1954, 
pages 187-219. ; 


Industrial Waste Disposal Charges in Cities 
over 5,000 Population, Special Report 
No. 18-S, American Public Works As- 
sociation, January 1955. 


Symons, James M., “Rate Formulas for 
Industrial Wastes,’ Water & Sewage 
Works Reference and Data Edition, Vol. 
102, No. 6, June 1, 1955, pages R-230- 
R-235. 


31 


This sewage treatment plant at 
Fillmore, Calif., was built in 1955. 
Designing engineer: Bennett En- 
gineering Co., Santa Paula, Calif. 
Consulting sanitary engineers: #, 
Harry N. Jenks and John H. Jenks, 

Palo Alto, Calif. 


Printed in U.S.A. 


rtland Cement Association 


East Sewage Treatment Plant, Bremerton, Wash. Because of its location, concrete retaining walls and sea walls 
were built in conjunction with this primary treatment plant. Carey and Kramer, Seattle, consulting engineers. 


Sewage treatment works, 
Kenyon, Minn. The walls of 
this building are of 8-in. 
architectural concrete. Bannis- 
ter Engineering Co., St. Paul, 
Minn., consulting engineer. 


Front Cover 


Sewage treatment plant 
at Pekin, Ill. Kinsey En- 
gineering Co., Pekin, 
consulting engineer, 


Copyright 1954 by Portland Cement Association 


Administration and laboratory 
building, Southside Sewage 
Treatment Plant, Oklahoma 
City, Okla. The exterior walls 
of this structure are 8-in. con- 
crete masonry units covered 
with shotcrete. Benham Engi- 
neering Co., Oklahoma City, 
consulting engineer. 


Sewage Treatment Works 


EFORE this country was settled by the white man, it was safe to drink 
B from almost any stream, river or lake in America. The savage had 
solved his sanitation problem—he protected himself, his family, and the mem- 
bers of his tribe by a frequent change of abode. 

Since then, civilization, with its ever-increasing population and industrial 
activity, has emptied practically everything into our waterways with little 
thought of the consequences. This condition must be corrected. 

Most authorities now predict a population of 200 million persons by 1975 
in the United States. America has become an urban nation, with three out of 
five persons living and working in cities, and the growth of urban communities 
has created urgent problems of sewage disposal. At the same time, the 
demand for clean water usable in home and industry has pyramided. 

In his Economic Report transmitted to Congress on January 28, 1954, 
President Eisenhower said: 

“The accumulated requirements of local water and sewerage facilities are 
impressive. To eliminate the backlog of water facilities within five years, and 
also provide for current growth of population, annual expenditures would 
have to come to about 1.2 billion dollars, compared with a current rate of 
0.5 billion. Even more serious is the shortage of sewers and industrial waste 
facilities, the capacity of which has not kept pace with the rapid urban 
growth of the last decade. To meet these requirements within five years, as 
well as to provide for current growth, annual expenditures of 1.8 billion 
dollars are necessary, which compares with a current rate of about 0.6 
billion.” 


WHY SEWAGE TREATMENT WORKS 
ARE NECESSARY 


Water and Health 


The failure to dispose properly of hu- 
man wastes was one of the primary 
causes of the frequent plagues and epi- 
demics in Europe in the Middle Ages. 
To curtail these outbreaks, systems of 
underground pipes or sewers were de- 
vised. Drinking water was piped from 
distant hills to great cities like Rome, 
and sewers carried the wastes to nearby 
waterways, such as rivers or lakes. As 
long as the wastes were greatly diluted 
by water they did not become dangerous 
to health. 

During the past century it was dis- 
covered that certain bacteria, which are 
tiny living organisms, cause diseases. 
These harmful bacteria were found in 
the feces of sick people and in polluted 
water. This knowledge was applied to 
water treatment to make contaminated 
water safe to drink by removing or kill- 
ing the harmful bacteria. Diseases like 
typhoid fever that used to kill thousands 
of persons each year have been brought 
under control. 

It is known, however, that there is an 
economical and practical limit to what 
can be accomplished in the treatment 
of drinking water. In many localities 
the rivers have become so polluted that 
there is grave question as to how much 
longer they can be used as a source of 
public water supply. 


4 


Scientific research is still going on in 
the field of water-borne disease. A prom- 
ising vaccine has been developed for use 
against the dread poliomyelitis. In the 
course of this work, it was definitely 
established that polio enters the body 
through the intestinal walls, a charac- 
teristic of all water-borne disease. The 
relationship between undulant fever and 
the water supply is still in doubt and 
the same is true of tularemia, or rabbit 
fever. 

Meanwhile, more people need larger 
quantities of potable water. The use 
per person is reaching toward 150 gal. 
per day and the rate is climbing steadily. 
Most larger cities now use surface water 
and those cities using the less contam- 
inated underground supplies are being 
forced to consider going to treated sur- 
face supplies because of falling water 
tables. Many cities now pipe water long 
distances because of contaminated lo- 
cal supplies. 


Uses of Clean Waters 


In addition to domestic water supply, 
there are other important needs for clean 
water. Industrial water usage was esti- 
mated to be 80 billion gal. daily in this 
country in 1950, and it is predictec 
that this tremendous demand on wate! 
resources will be increased to 215 bil 
lion gal. daily by 1975. Much of thi 


Beach scene in California. Unpolluted waters are a valuable asset to any community. Protect 
your waters against pollution by treatment of sewage and industrial wastes. 


industrial water must be of excellent 
quality. A basic consideration in the lo- 
cation of an industry is the quantity and 
quality of water available in the area. 
As civilization grows more complex 
and leisure time more abundant, the 
need for healthful recreation increases. 
~The bathing beach, the ol’ swimmin’ 
hole, the trout stream or the picnic by a 
babbling brook—all are important rec- 
-Teational activities which are necessary 
in our lives. In many areas the resort and 
aeration industry is the most impor- 
tant business. The family car is used by 
millions of people to get out for a week- 
end in natural surroundings. All these 
things are threatened by wastes being 
dumped in natural waters. In many cases, 
ur creeks and rivers bear little resem- 
lance to the clear, inviting streams of 
resterday. 
_ There are important agricultural uses 
or water from lakes and streams. They 


are often used to water beef and dairy 
cattle and other livestock, and crop ir- 
rigation alone is estimated to require 
almost 100 billion gal. of water daily. 
Livestock have been killed by drinking 
water containing chemical poisons dis- 
charged by industrial plants. Most milk 
ordinances prohibit the sale of fluid milk 
from dairy cows watered in polluted 
streams. Polluted agricultural water sup- 
plies become more serious when it is 
considered that a rapidly increasing pop- 
ulation means that food supplies must 
be increased accordingly. 

Many people do not stop to realize 
that water must be used and re-used by 
the next city or industry downstream. 
On many of the great rivers of America, 
the waters are re-used dozens of times 
before they reach the ocean. The same 
is true of the Great Lakes. There is not 
enough water available for each city to 
have an adequate, usable supply and at 


> 


Activated-sludge sewage treatment plant, Noblesville, Ind. Henry B. Steeg and Associates, 
Indianapolis, Ind., consulting engineers. Pollution abatement will be attained when each com- 
munity builds an adequate plant for the treatment of its wastes. 


the same time to use the water as a 
means of unrestricted waste disposal. 


What Is Pollution? 


Sewage and industrial wastes are 
themselves polluted waters. The pollu- 
tion consists of small amounts of grease, 
soap, waste food particles, paper, chem- 
icals, discharges from the human body, 
etc. These materials are mixed in the 
liquid in a dissolved or suspended state, 
as salt and pepper are mixed in soup. 
The salt is dissolved but the pepper par- 
ticles are suspended in the soup during 
stirring and settle to the bottom when 
stirring ceases. These waste materials 
may be either mineral or organic mat- 
ter. The difference is that the organic 
matter will rot or decay, while the min- 
eral will not. 

When sewage and industrial wastes 
are mixed with natural waters, they pol- 
lute the stream or lake. The amount of 
dilution available determines the level 
of pollution. Sewage always carries the 
agents of its own destructicn in the form 
of millions of useful microscopic bac- 
teria which consume the organic mate- 
rial in the sewage as food. This action 


6 


is the basis for the natural purification 
of water. 

The important fact in the natural pur- 
ification of water is that dissolved oxy- 
gen in the water is required for these 
helpful bacteria to work. Because cities 
have grown large and close together, the 
amount of sewage has become too great 
to be handled by these natural processes 
without depleting the oxygen dissolved 
in the water. As a result, the water grows 
progressively more polluted, more dan- 
gerous to health and less desirable for 
re-use. 

Pollution abatement does not aim at 
keeping the sewage and industrial wastes 
out of the streams entirely, for this would 
be uneconomical, impractical and a 
failure to use water resources wisely. 
Rather, the aim is to treat the sewage 
to remove almost all of the impurities 
that cause pollution before discharging 
the effluent into a natural waterway. This 
can be accomplished only at the source, 
which is the end of the city sewer system. 
It therefore becomes the moral and legal | 
responsibility of each community and in- 
dustry to clean up its own mess. In this. 
way the community’s own health and 
that of its neighbor will be improved. | 


WHAT IS SEWAGE TREATMENT? 


EWAGE treatment is not a mysteri- 
*s Ous process. Contrary to popular 
belief it does not involve the extensive 
use of chemicals except in special cases. 
Modern treatment facilities merely speed 
up the forces of nature instead of allow- 
ing them to occur over a much longer 
period in a stream or lake into which 
the sewage might empty. Involved are 
the action of gravity in the settling of 
Suspended solids, aeration and the ac- 
tion of bacteria and other living organ- 
isms which use the sewage as food. 
The purpose of treatment is to sepa- 
rate from the Se€wage as much of its 
Suspended solids as possible and to sub- 
ject them, as well as the liquid, to proc- 
esses which will render them suitable 
for final disposal. Naturally, the degree 
of treatment varies with circumstances. 
Factors such as the amount and char- 
acter of the domestic sewage and indus- 
trial wastes, as well as the size, condition 
and use of the outlet stream, determine 
how much treatment should be provided 
in each case. For example, a small town 
Ma river as large as the Mississippi may 
teed to provide only minimum treat- 
nent while cities such as Chicago and 
New York must provide considerable 
-eatment even though they are situated 
Nn large bodies of water. Therefore, sew- 
ge May require partial treatment or 
°omplete treatment depending upon 
‘cal conditions. 


Partial or Primary 
Treatment 


Partial or primary treatment consists 
of the separation of the settleable solids 
from the liquid, disposal of the solids in 
an approved manner, and the discharge 
of the liquid either without further treat- 
ment or after disinfection. Grease, scum, 
other floating material and settleable sol- 
ids removed by primary treatment fa- 
cilities represent 30 to 40 per cent of 
the organic material found in sewage. 
Treatment units or processes which may 
be included in this first phase of disposal 
are screens, grit chambers, sedimenta- 
tion basins, chemical precipitation, chlo- 
rination, and Sludge digestion, drying 
or disposal facilities. These units and 
processes and their functions will be 
discussed later, 


Complete Treatment 


In the foregoing Paragraph we have 
outlined primary treatment facilities 
briefly and mentioned that only about 
one-third to one-half of the organic ma- 
terial in the sewage is removed by this 
portion of the treatment process. The 
organic material remaining is mostly in 
a dissolved state. Therefore, if complete 
treatment is necessary, additional proc- 
esses known as secondary treatment 


Fig. 1. Flow diagram of a typical 
sewage treatment plant. 


must be provided to reduce these im- 
purities further. Secondary treatment fa- 
cilities are biological processes which 
are capable of removing up to 95 per 
cent of the organic material and which 
include such units as intermittent sand 
filters, trickling filters, or the activated- 
sludge process. These also will be de- 
scribed in more detail later. 


Selection of Type of 
Treatment 


Many factors must be considered in 
selecting the type of treatment best 
suited for a given community. Among 
these are the cost, the population to be 
served, the type of sewage to be han- 
dled, the nature and amount of indus- 
trial wastes which may be discharged to 
the sewers, and the size, condition and 
use of the outlet stream. 

Municipalities contemplating the 
construction of sewage treatment works 
should employ a competent sanitary en- 
gineer experienced in this field to assist 
the local engineer in designing the plant. 
It is no reflection on the ability of the 
local engineer to provide him with such 
assistance, for sewage treatment is a 
highly specialized subject. Governmen- 
tal agencies should be contacted, such 
as the state health department, the state 
stream control agency, etc. Determina- 
tion of the degree of treatment necessary 
as well as the approval of the final plans 
is usually a function of one or more 
state departments. 


8 


RAW SEWAGE FROM SEWERS 
a 


BAR GRIT 


SCREEN CHAMBER 


PRIMARY 
TREATMENT 


SLUDGE 
DIGESTER 


Operation of Treatment 
Facilities 


Sewage treatment facilities, either sim- 
ple or complicated, cannot be expected 
to operate without supervision. The 
number and caliber of operating per- 
sonnel required will depend, of course, 
upon the size and type of the installation 
and the number and complexity of the 
necessary laboratory control tests. 

Provision for adequate operation and 
maintenance costs should be made in 
the annual budget to assure proper oper- 
ation of the equipment. Since a consid- 
erable capital investment is represented 
by a sewage treatment plant, it is poor 
economy to shorten useful equipment — 
life with inefficient operation. Poor oper- 
ation may threaten the health and wel- 
fare of down-stream water users and © 
result in suits against the offending city. | 

Adequate operational records help in — 
obtaining efficient operation. Such rec- | 
ords are invaluable in the public rela- 
tions job of informing the citizen about 
the services he receives from the sewage 
plant in return for his tax dollars. 


TRICKLING FILTER 
PRIMARY Fp Beara areca 
SETTLING TANK PUMP 


== 


SECONDARY 
SETTLING TANK 


CLEAN WATER TO STREAM 
—— eS Sa 


CHLORINATION 
TANK 


| 
SECONDARY 
| 


TREATMENT 


HOW SEWAGE WORKS ARE FINANCED 


Wes a municipality has decided to called, may include: 


construct a sewage treatment 1. A contiguous area comprising a 
works, the question of financing the im- Tegion or drainage area in one or 
Provement is of major importance. The more counties, including the mu- 
treatment of sewage may be more than nicipalities therein. 

| 4 municipal problem, since areas out- 2. A single municipality with or with- 
| side the corporate limits may also re- Out adjoining unincorporated 
quire treatment works but may be un- areas, 
__ able to finance separate facilities. 3. A portion of a municipality. 


In some states the Creation of a dis- 
trict is possible under general law; in 
others new laws would be necessary. It 
should be established at the outset 

For this reason and because of con- _ whether or not a separate organization 
_ Stitutional debt limitations, it may bede- _ is desirable, what area it should include 
sirable to form a separate organization —_and the need for additional legislation. 
whose specific Purpose is to intercept After careful consideration of all the 
ind treat sewage. Such organizations _ facts, these questions should be decided 
ave taxing and financing powers dis- in consultation with Officials, engineers 
inct from those prescribed by state law and attorneys of the municipalities in- 
or the individual municipalities. These volved and the state health department 
anitary districts, as they are sometimes or other interested state agencies, 


Organization of District 


Methods of Financing* 


There are four principal methods of 
financing sewage treatment works: 

1. General tax obligation bonds. 

2. Special assessments. 

3. Service charge revenue bonds. 

4. Combination method. 

General Tax Obligation Bonds—This 
method considers the improvement to 
be of general benefit to all property ac- 
cording to its assessed valuation. The 
sewage works is not considered in this 
method as a separate utility but as a 
part of the municipal governmental 
function and, therefore, as a general tax 
upon all property. 

Special Assessments — The special 
assessment method of financing is based 
upon the taxing of real estate in propor- 
tion to the benefits occurring through 
increased valuation. This method does 
not consider payment in proportion to 
the service rendered. 

Revenue Bonds—The revenue bond 


*See also “Fundamental Considerations in 
Rates and Rate Structures for Water and 
Sewage Works,” Ohio State Law Journal, 
19 5iep Violael2=s Nowe 


PUBLIC 


HE subject of sewage treatment is 
Pats concern of every citizen. For 
health, as well as economic and recrea- 
tional considerations, pollution of our 
surface waters must be stopped. In 
many instances these waters are the only 
source of our public water supply. Their 
pollution may cause outbreaks of water- 
borne diseases, endanger seafoods, cur- 
tail industrial development, depreciate 


10 


method of financing considers the im- 
provement as a utility and provides for 
payment of the bonds from revenues 
without adding to the general tax debt 
of the community. Usually, the charge 
for sewer service is based on a percent- 
age of water consumption, but other 
factors which may be deemed equitable 
may be considered in establishing a rate 
structure. 

Combination Financing — Financing 
of anentire project may be accomplished 
by combining any or all of the above 
described methods to fit the overall 
financing plan for the municipality. 
Service charges may be made even 
though a project may not be financed 
with revenue bonds, and such income 
may be used to retire general obligation 
sewerage bonds. 

A more detailed discussion of the 
steps necessary in financing a sewage 
works project may be found in the book- 
let entitled Financing Sewerage Works, 
published by the Portland Cement Asso- 
ciation and furnished free on request. 
Distribution is made only in the United 
States and Canada. 


SUPPORT 


property values, destroy recreational 
areas and prohibit water sports such as 
swimming, boating and fishing. 

If a city needs sewage treatment 
works or extensions to an existing plant 
to make it more efficient, public support 
of such an improvement is highly desir- 
able. | 

To obtain this support educational 
campaigns are effective. Newspaper ar 


ticles, advertisements, posters, booklets, 
lectures, radio talks, etc., have been used 
to advantage in acquainting citizens with 
the nature and necessity of the proposed 
project, its probable cost and method of 
financing. The aid of local organizations 
such as civic, professional and social 


clubs in such a campaign does much to 
assure its success. Whatever methods 
are used, a full discussion of all the facts, 
especially costs to the individual, is 
essential. Poorly advertised meetings or 
meetings held in secret will fail to gain 
this desirable public support. 


SEWAGE TREATMENT 


S HAS been mentioned, sewage treat- 
ment is a speed-up of such forces 
of nature as gravity, aeration and the 
action of bacteria and other living or- 
ganisms. The following is a brief de- 
scription of how the various units and 
processes of a sewage treatment works 
utilize these forces in reducing the im- 
purities of the sewage. 

The force of gravity is utilized to set- 
tle out organic and inorganic matter 
which is suspended in the sewage. The 
process involves a reduction in the veloc- 
ity of flow and the retention of the sew- 
age in tanks for a period of time. Such 
tanks are universally built of concrete. 

The biological process to which both 
the dissolved and undissolved organic 
matter in the sewage are subjected 
involves living organisms such as bacte- 
tia. These feed upon the organic matter 
and by their life processes reduce the 
impurities in the sewage. In fact, treated 
Sewage effluent is often used for farm 
irrigation or industrial process water. 

Bacteria enter sewage from several 
sources but the majority are contributed 
by human and animal excreta. Two 
types of bacteria, aerobic and anaerobic, 
ire responsible for the decomposition 
f the organic matter in the sewage. 
30th require oxygen. The aerobic de- 


mand free oxygen while the anaerobic 
obtain their supply from the chemical 
compounds present in their surround- 
ings. Thus, anaerobic bacteria are uti- 
lized for the decomposition of sewage 
solids in digesters while aerobic bacteria 
work on the impurities in the liquid in 
filters and aerators. Since aerobic bacte- 
ria require free oxygen, aeration of the 
sewage is necessary in some of the proc- 
esses Of sewage treatment which are 
described later. Anaerobic bacteria pro- 
duce noxious odors and inflammable 
gases while aerobes produce little odor 
in their life cycle. 

Since aerobic bacteria require oxygen 
for growth and activity in causing the 
decay of organic matter, it is apparent 
that they will use more oxygen in the 
conversion of sewage of a greater 
strength than in the conversion of a 
weak sewage. This fact is relied upon 
in one of the tests used in determining 
the concentration of sewage. The test 
indicates the volume of oxygen required 
for aerobic decomposition, or decay, of 
sewage and is called the Biochemical 
Oxygen Demand in the sewage. It is 
commonly known as the B.O.D. test. 
The B.O.D. of the average municipal 
sewage is in the order of 250 parts per 
million. 


11 


Bar screen and grit chambers, 
South Side Sewage Plant, Okla- 
homa City, Okla. Benham Engi- 
neering Co., Cklahoma City, con- 
sulting engineer. 


TREATMENT METHODS 


Primary or Partial Treatment 


As previously indicated, primary 
treatment consists of the separation of 
suspended matter from the liquid, prop- 
er disposal of the solids, and discharge 
of the liquid. A brief description of the 
various processes and units which might 
be included in a partial treatment works 
is given in the following paragraphs. 


Screening—The screen is usually the 
first step in any treatment works. (See 


12 


~ 


photo above.) It is used to intercept 
floating or coarse suspended solids 
which might otherwise clog sewage 
pumps or pipe lines. It consists of a 
series of evenly spaced, parallel metal) 
bars installed at an angle in the sewage 
channel. The material which is caught 
by the screen may be removed manually 
or mechanically and disposed of by 
burial or incineration. An improvemen 
of the screen is the comminutor, whicl 
grinds the material it intercepts and re 
turns it to the sewage flow. 


Grit Chambers—A grit chamber is a 
narrow, rather shallow concrete channel 
constructed to reduce the velocity of 
flow to the point where heavier, inert 
particles in sewage, such as sand, cin- 
ders, etc., settle out, leaving organic 
particles suspended in the flow. Grit is 
removed because it tends to clog pipes, 
Cause excessive wear in sewage pumps 
and occupy needed space in the digester. 
Grit chambers are essential when the 
sewage contains drainage from streets 
and alleys and are desirable in highly 
mechanized treatment plants. 


Settling Tanks—A settling tank is 
usually included in any sewage treat- 
ment works. It is made so that the sew- 
age flows through it even less rapidly 
than through the grit chamber. The de- 
creased velocity permits more suspend- 


ed particles to settle or sink to the bot- 
tom, yet the size of the tank is such that 
any portion of sewage entering will pass 
through in about two hours. Various 
types have been devised, including plain 
sedimentation tanks, septic tanks and 
Imhoff tanks. 

A plain sedimentation tank may be 
rectangular or circular. In the rectan- 
gular tank the sewage enters at one end 
and flows through the length of the tank. 
In the circular tank, sewage enters 
through a submerged pipe to the center 
of the tank and then flows radially to an 
outlet which extends around the entire 
rim. The settled material, called sludge, 
is collected in a hopper in one portion 
of the basin by an electrically driven 
scraping mechanism. The sludge thus 
collected is pumped several times a day 
to sludge digestion tanks or disposed of 


Settling tanks, sewage treatment plant, Reading, Pa. These concrete tanks are 10 ft. deep and 
-have 8-in. walls. Robert Chubb, city engineer, Reading. 


Sewage treatment plant, Rayne, La. In the right backgro 
consulting engineer. 


Imhoff tank. L. J. Voorhies, Baton Rouge, cir 


in some other satisfactory manner. 
Septic and Imhoff tanks differ from 

plain sedimentation tanks in that the 

solids which are deposited are not re- 


und is an exterior view of a concrete 


moved daily but accumulate in the lower 
portion of the tank, where they undergo 
anaerobic decomposition. These tanks 
are therefore designed with greater Ca- 


This is a top view of a concrete Imhoff tank at Middleburg, Pa. Gannett, Fleming, Corddry and 


Carpenter, Inc., Harrisburg, Pa., 


consulting engineer. 


Chemical precipitation-settling unit of prestressed concrete, Bakersfield, Calif. Clyde C. Kennedy, 
San Francisco, Calif., consulting engineer. 


pacity to provide for several weeks’ ac- 
cumulation of sludge. 

In the septic tank, settling occurs in 
the same compartment in which the 
solids are decomposing. As a result the 
settling efficiency is decreased because 
of rising gas bubbles. Septic tanks are 
used only for very small installations 
such as institutions, trailer camps, rural 
homes, etc. 

The Imhoff tank (see photos on page 
14) is an improvement of the septic 
tank. It is designed to prevent gas bub- 
bles from rising through the sewage 
and thus has increased efficiency. It is 
‘sometimes referred to as a two-story 
tank since it is a tank within a tank. The 
Upper tank is the settling compartment 
hrough which the sewage flows. It is 
rovided with a slotted bottom through 
hich the solids pass into the lower or 
igestion compartment. A_ baffle ar- 
nhgement prevents the gases of the de- 


composing solids from rising through 
the sewage in the settling compartment, 
thus improving settling. 

Chemical Precipitation — Chemical 
precipitation is used to increase the 
quantity of suspended material removed 
from sewage by settling. The process 
consists of adding chemicals to the sew- 
age, such as ferrous sulfate, aluminum 
sulfate, etc. These will react with sub- 
stances normally present or with other 
substances also added for this purpose 
in order to bring together small particles 
of material which will not normally set- 
tle. The particles which are brought to- 
gether form a mass of material which 
will settle more readily than the in- 
dividual or separate particles under 
favorable conditions. This method will 
double the efficiency with which sus- 
pended material is removed, but it is 
used only under special circumstances 
because of increased operational cost. 


Me) 


Concrete digester and control house, sewage treatment plant, Peru, | 


Quinlan, Chicago, Ill., consulting engineer. 


Sludge Digestion—Sludge digestion is 
the process which renders sludge more 
suitable for final disposal by making it 
less offensive to sight and smell and by 
greatly reducing its volume. The process 
is carried on in sewage works by anaero- 
bic bacteria in either the lower compart- 
ment of an Imhoff tank or in specially 
designed tanks called digesters used with 
plain sedimentation tanks. 

Since the rate of digestion increases 
with temperature, heating the sludge is 
helpful and is commonly done where 
digestion tanks are provided. Heating 
the sludge in septic and Imhoff tanks 
is impractical. 

The gas generated by the digestion 
process is burnable and, in certain con- 
centrations, highly explosive. In many 
sewage treatment works this gas is col- 

lected and utilized to heat buildings and 
digesters, and for fuel in gas-driven en- 
gines for pumps and generators. A re- 


16 


Il. Consoer, Townsend & 


cent use has been to recirculate this gas 
for sludge mixing in the digesters. 


Sludge Drying—Sludge from the sew- 
age treatment process may be dewatered 
either before or after it has undergone 
digestion or decomposition. Its mois- 
ture content depends upon its condition. - 
Raw (undigested) sludge contains ap- 
proximately 98 per cent moisture while | 
digested sludge may have as low as 85 
per cent moisture content. Common 
methods of dewatering are sludge drying) 
beds and sludge filters. 

Sludge drying beds are usually rec 
tangular and consist of graded grave) 
overlaid with about 6 in. of sand. Th} 
bed is drained by open-joint tile and |) 
usually exposed to the sun and air bi} 
may be enclosed in glass similar to | 
greenhouse (see photo on page 18). } 
operation, sludge is discharged onto t)) 
bed to a depth of about 8 to 10 in. Dra 


Digester under construction, sewage treatment plant, East Providence, R.l. Precast concrete 
plank were used on the floating cover in preference to less durable materials. Charles A. Maguire 
and Associates, Providence, consulting engineers. 


Open sludge drying beds with concrete walls, sewage treatment plant, College Station, Texas. 
E. W. Steel, Austin, Texas, engineer. 


Aeration tanks, activated-sludge sewage treatment plant, 


sii 


Pottstown, Pa. Note glass-enclosed 


sludge drying beds in the background. Albright and Friel, Philadelphia, Pa., consulting engineers. 


age and evaporation reduce the volume 
of well-digested sludge to about 50 per 
cent in a week or two; then the moisture 
content is such that the sludge can be 
removed from the bed with forks or 
shovels. There is very little odor to 
dried, well-digested sludge. On the other 
hand, fresh or incompletely digested 
sludge dries less rapidly, produces ob- 
jectionable odors, and forms a breeding 
place for flies. 

Sludge filters may be used to dewater 
either raw or digested sludge. The filter 
is a cloth-covered cylinder which rotates 
partially submerged in a container into 
which the sludge is introduced. Sludge 
is picked up on the cloth of the filter by 
4 vacuum which dewaters it. 


18 


Disposal of Sludge—Either raw OF 
digested sludge may be disposed of be- 
fore or after dewatering. Cities near the 


coast have barged the wet sludge out to 
sea for disposal. Wet sludge has been 


discharged into streams Or lakes during 


periods of high flow, but this may lea¢é 


to stream pollution. Wet sludge may be 
discharged into lagoons OF be spreac 
upon farm land and plowed under. 


Dewatered sludge can be disposed ¢_ 


on dumps, it can be incinerated, OF 

can be used as a fertilizer if proper! 
prepared and applied. Its value depen 
upon the type of sludge. Heat-drie 
activated sludge appears to have tl 
highest commercial value. For examp 
plants at Milwaukee, Wis.; Austiy 


| 


| 


Texas; Chicago, Ill., and many other 
cities produce commercial fertilizer as a 
part of their sewage treatment program. 


Complete Treatment 


In the primary facilities described 
above, approximately two-thirds of the 
organic material present in the dissolved 
and suspended state is not removed. 
Therefore, if complete treatment is nec- 
essary an additional process known as 
secondary treatment is accomplished by 
the use of intermittent sand filters, trick- 
ling filters, or the activated-sludge proc- 
ess. Final settling tanks are required in 
the activated-sludge process and are 
generally used with trickling filters. 


Intermittent Sand Filters—An inter- 
mittent sand filter consists of a bed of 
graded sand and gravel adquately un- 
derdrained by Open-joint sewer pipe. 
The surface of the sand bed is flooded 
intermittently with sewage. Bacteria and 
other lower forms of life feed on the 
Sewage in the bed. The aerobic bacterial 
action in the porous bed produces an 
effluent of very high quality. Sand filters 
are not used except in small installa- 
tions, however, because of the large 
land area required and the large amount 
of hand labor involved in cleaning and 
maintenance. 


Trickling Filters—Trickling filters are 
*omposed of underdrained beds of 
tone 3 to 10 ft. deep with the stone of 
niform size for maximum permeabil- 
y. After the solids are removed, sew- 
3¢ is applied to the surface of the filter 
ad flows over and downward through 
‘© stone. This stone soon becomes 
ated with aerobic bacteria, which are 


; 
: 


the workmen of the trickling filter. It is 
their action which brings about the pu- 
rification accomplished by this unit. 
These bacteria eat the small particles 
of organic matter or impurities present 
in liquid and thereby improve its con- 
dition. This coating on the stone gradu- 
ally increases in thickness until it finally 
peels off or unloads and is carried away 
in the liquid. To keep this material from 
entering the outlet stream, a final set- 
tling tank is necessary. The liquid must 
pass through it before being discharged 
into the outlet stream. 


Sewage is applied to the filter either 
through spray nozzles or rotary distrib- 
utors. Spray nozzles spaced 12 to 15 ft. 
apart are installed at the surface of the 
Stone and sewage flows to the nozzles 
through distributor Pipes. Rotary dis- 
tributors are frequently used in connec- 
tion with circular beds and the majority 
of the more recent installations utilize 
this system. Sewage is conducted 
through a horizontal conduit to a ver- 
tical pipe in the center of the filter. Two 
or more horizontal pipes or arms are 
fastened to this center supply pipe only 
a few inches above the surface of the 
stone in the filter. Sewage flows through 
these arms and onto the filter through 
Openings spaced at intervals. The force 
of the sewage flowing through the arms 
Causes the distributor to revolve in the 
Same manner as a lawn sprinkler, there- 
by spraying the entire surface of the 
filter. 


Until recently, trickling filters were 
designed for what is now called low-rate 
Operation, or application of sewage at 
a rate of 1 to 3 million gal. per acre of 
filter surface per day. In the last few 
years, high rate operation (16 to 30 mil- 
lion gal. per acre per day) has been 


19 


practiced. Although low-rate filters have operation, however, and turn out a less 
been used satisfactorily for many years, stable effluent. 

high-rate filters have the advantage of 

being smaller and therefore cheaper to Activated-Sludge Process — In this 
construct. They require greater care in method of treatment a suspension of 


Trickling filters at sewage treatment plant, East Providence, R.I. Filter underdrains were formed 
of precast concrete beams as shown in lower picture. Charles A. Maguire and Associates, Provi- 
dence, consulting engineers. 


Very compact activated-sludge sewage treatment plant, Pinckneyville, Ill., built in 1938. Building 
and Engineering Service Corp., Decatur, Ill., engineer. 


living aerobic organisms in the form of 
a flocculant material is built up in the 
liquid itself rather than as an attached 
scum on filter rock. The organisms in 
the suspension feed upon the organic 
Material that surrounds them and re- 
duce the amount of impurities in the 
‘wage. This is done in a unit known 
\s the aeration tank. Compressed air is 
orced through the liquid, or the sur- 
ace is mechanically agitated so that air 
} €ntrained. This aeration supplies the 
ygen required by the organisms and 
“eps them in intimate contact with 
\€ sewage. 
After the aeration process the sewage 
‘tun into a final settling tank before it 


is discharged into the outlet stream. The 
settled particles are teeming with bac- 
teria needed in the aeration tank to ac- 
complish purification. Therefore, this 
settled material is continually pumped 
from this final tank back to the aeration 
tank, with any excess going to the di- 
gester or to the primary settling tank. 
This process is capable of reducing the 
biochemical oxygen demand of the sew- 
age by as much as 90 to 95 per cent. 

The activated-sludge process is fre- 
quently adapted to very compact, unit- 
type sewage plant designs called pack- 
age plants. Such plants take advantage 
of the common-wall principle and are 
ordinarily equipped with a variety of 


21 


automatic controls to facilitate opera- 
tion, Activated-sludge plants, in gen- 
eral, require a more capable operator 
than the trickling-filter type of plant. 


Chlorination—Chlorination of either 
raw or treated sewage May be desirable, 
depending upon local conditions. It is 
generally used for disinfection, odor 
control or the prevention of undesir- 
able growths. 


Other Processes—The foregoing dis- 
cussion describes briefly some of the 
more common units which are utilized 
in sewage treatment works; it is not a 
complete treatise on this subject. There 
are other processes and units which are 
being used satisfactorily in sewage treat- 
ment. In addition, there are many modi- 
fications and combinations of the meth- 
ods described such as recirculation, 
step-aeration, pre-aeration, storage of 
activated sludge for shock loads, filtra- 
tion and activated-sludge combinations, 
and aerobic sewage lagoons used in 
secondary treatment. 


Service Buildings 


Service buildings to house office, lab- 
oratory and equipment are a necessary 
part of a sewage treatment works. Ar- 
chitectural concrete or concrete ma- 
sonry is admirably suited to the con- 
struction of such buildings. Attractive 
structures of distinctive modern design 
may be provided at reasonable cost. 
The clean-cut lines of an architectural 
concrete building surrounded by well- 
planned, landscaped grounds will be an 


22 


attractive asset to any community. 

A typical service building in archi- 
tectural concrete at Bakersfield, Calif., 
is shown on the back cover. Additional 
examples will be found in a leaflet Sew- 
age and Waterworks Plants in Archi- 
tectural Concrete, published by the 
Portland Cement Association, which 
will be furnished free on request. Dis- 
tribution is made only in the United 
States and Canada. 


Concrete In Sewage Plants 


Concrete is used for sewage plants in 
relatively thin-walled hydraulic struc- 
tures, as well as for buildings. Since 
these. structures undergo severe €XpO- 
sure to freezing and thawing, wetting 
and drying, mild chemical corrosion, 
etc., it is extremely important that con- 
crete of high quality be used in con- 
struction. A durable concrete that is 
also watertight may be obtained by 
using: 


1. Structurally sound aggregates of 
low porosity. 

2. A portland cement paste of low 
water-cement ratio. 

3. A properly designed air-entrained 
mix. 

4. Proper placement. 

5. Adequate curing. 


Detailed information on the produc: 
tion of quality concrete may be foun¢ 
in the publication Design and Contro' 
of Concrete Mixtures, available on re 
quest from the Portland Cement Ass¢ 
ciation. Distribution is made only in th 
United States and Canada. | 


Architectural concrete sewage treatment plant, Atlanta, Ga., built in 


1937. Wiedeman and Singleton, Inc., Atlanta, Ga 


-, consulting engineer. 


Sewage treatment plant, Austin, Texas, showing three architectural concrete 
buildings. These are, from left to right, laboratory and office, screen house, 
and the blower building. G. S. Moore, Austin, Texas, designing engineer. 


The activities of the Portland Cement Association, a national organization, are limited to 
scientific research, the development of new or improved products and methods, technical 
service, promotion and educational effort (including safety work), and are primarily de- 
signed to improve and extend the uses of portland cement and concrete. The manifold 
program of the Association and its varied services to cement users are made possible by 
the financial support of over 70 member companies in the United States and Canada, en- 
gaged in the manufacture and sale of a very large proportion of all portland cement used 
in these two countries. A current list of member companies will be furnished on request. 


Architectural concrete building, sewage treat- 
ment plant, Bakersfield, Calif. Currie Engineering 
Co., San Bernardino, Calif., consulting engineer. 


AT A s $ PF, Pee 10 


es eee 


steetie 


Table of Contents 


Introduction §..uits seen 2s ae ae ene ea oie 2 
‘Types: of Floor Systemsany an oes a bate es: 3 
One-Waypoystems ogee dns. 5, .re ae ene ae 3 
Two-Way Dystemsa.). tation ol oc) ayer Renee 3 
Supporting Members... aio. sues ee 4 
Mat-Slab Systems ne an dont cit, tate eet ee 5 
Modifications to the Basic Floor Systems........ 6 
Selection of Most Economical Floor System....... ¢ 
Special Design’ Detailecey nus. b a oer ee 9 
Designs of Typical Floor Systems................ 12 
One-Way, solid Slabs tua ye pete coe te cee ean 12 
One-Way Joists—20-In. Metal Pans............. 14 
One-Way Joists—16-In. Filler Block............ 15 
Flat ‘Plates’ ¥, cotepuse castrate homie sepals cere eee 16 
Flat Plates— Waffle Construction............... ie 
Flat Slabs? oqo Wie gree Ness) reel A gai 18 
Two-Way Solid Wslabsee -gni J ee anaes te 19 


Reinforced Concrete Floor Systems 


INTRODUCTION 


Reinforced concrete floors may be adapted easily and eco- 
nomically to any floor requirement. There are at least 
three basic types of concrete floor systems, the one-way, 
two-way and flat slab, and there are many combinations 
and modifications of these basic types to satisfy various 
functional and structural requirements. 

Concrete floors may be designed to expedite construc- 
tion and reduce story height of office, apartment, hospital 
or other commercial buildings; or they may be built to 
provide smooth, permanent, exposed concrete ceilings 
suitable for residential use. The wide variety of concrete 
floor systems available gives the architect or engineer a 
broad selection for his particular situation. This booklet 
is intended to assist him in making his choice. 


The drawings in this publication are typical designs and 
should not be used as working drawings. They are intended 


to be helpful in the preparation of complete plans which 
should be adapted to local conditions and should conform 
with legal requirements. Working drawings should be pre- 
pared and approved by a qualified engineer or architect. 


Copyright 1956 by Portland Cement Association 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and { 
educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services 

to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all — 
portland cement used in these two countries. A current list of member companies will be furnished on request. 


Types of Floor Systems 


ONE-WAY SYSTEMS 


A one-way solid floor slab designed to carry load in one 
direction is shown in Fig. 1. Although this type of floor is 
common because of its simple design and construction, 
it is generally restricted to use in short spans because of 
its excessive dead weight. These floors are suitable for 
heavy loads on spans up to about 15 ft. 

Various methods may be used to reduce dead weight 
and yet retain practically the same carrying capacity. A 
common method is to eliminate the concrete that pro- 
vides little or no resistance to moment. This is accom- 
plished in concrete joist floors formed by pans (Fig. 2) or 
filler block (Fig. 3), and in hollow slabs cored with paper 
tubes (Fig. 4). 

In the joist floor shown in Fig. 2, pans supported on 
shored joist soffits form the underside of the floor. These 
pans are generally available in 20- or 30-in. widths and 
in depths varying from 6 to 14 in. in 2-in. increments. 
Most pans are removable, although thin-gage corrugated 
units, which are sometimes used, can be left in place. 
Pan-joist floors are economical for light loads on fairly 
long spans. Since considerable concrete is displaced by 
the pans, shear at the support is often a controlling factor; 
for this reason special end pans are available that taper 
as indicated in Fig. 2. When tapered ends are used, shear 
must be investigated at the beginning and end of the taper 
and in some instances it is also necessary to investigate 
stresses due to negative moment at these two sections. 

Variation in joist width to meet specific design require- 
ments is easily obtained by altering the spacing of pans. 
A minimum joist width of 4 in. is specified by the ACI 
Code.* A minimum slab thickness of 2 in. is also specified 
_by the code but special conditions other than moment 
requirements may dictate the use of thicker slabs. 

Another method of reducing dead weight in one-way 
slabs is to use filler block. This type of joist floor is 


*American Concrete Institute, ‘Building Code Requirements for 


Reinforced Concrete (ACI 318-51).” 


Fig. 1. The one-way solid slab, supported by beams that frame into gir- 
ders and columns, is a conventional floor system that is easily and 


quickly designed. 


economical for light to intermediate loads on medium 
spans and, in contrast to joist floors formed by pans, it 
presents a smooth undersurface that may be left untreated 
as the finished ceiling. 

Paper tubes placed in the forms before the concrete is 
cast will also reduce dead weight. These cored, hollow 
slabs look like solid slabs when they are finished. 

Portland cement paint may be applied directly to the 
underside of most types of concrete floors. Generally, 
painting the exposed concrete is more economical than 
applying other types of ceiling finish and is equally 
acceptable. 


TWO-WAY SYSTEMS 


Two-way floor systems, as the name implies, are reinforced 
to carry load in two directions. A typical two-way panel is 
illustrated in Fig. 5. Whether a slab acts as a one-way or 
two-way slab depends solely on the dimensions of the 
panel; it is not a matter of design convenience. Consider 
the simple structure shown in Fig. 6, in which two beams 
having the same moments of inertia and a span ratio of 
4 to | intersect at their centers. A load placed at the point 
of intersection causes the beams to deflect equally since 
they are integral at the joint. From the equation for 
deflection of a simple beam it may be determined that 
the load taken by the long span is 1/64 of that taken by 
the short span. For practical purposes it may be assumed 
that the short beam carries all of the load. If the span 
ratio were 2 to l, the usual dividing ratio between one- 
and two-way floors, the load taken by the longer span 
would be only about 10 per cent of the total load. 

In Fig. 6 the load P is shown transmitted to reactions 
at the ends of the beams. In the analysis of an entire 
floor panel or bay, the effect of end reactions on support- 
ing members must also be included. A study of Fig. 7, 
which illustrates the distribution of a load in a two-way 
system, shows that the sum of the moments across a bay 


Fig. 2. Concrete joist floors formed by removable metal pans are eco- 
nomical for long spans and light uniform loads. Shear requirements 
dictate the use of tapered pans near the supports. 


must equal the moment produced by one-way action for 
the full load.* Therefore, the problem in the design of any 
type of floor that has two-way action is not the determina- 
tion of total moment acting across the full panel width 
at various sections but the distribution of this moment 
along the sections. The design is simplified by assuming 
uniform distribution of moment across bands or strips 
usually taken as half the bay width. 

The ACI Code presents two methods for designing two- 
way floor systems. In Method 1, moments and shears at 
critical locations in the floor panel are calculated as per- 
centages of the moments and shears at these locations 


*Since the panel is square, the load taken by each interior beam is 


5 If torsional restraint of the exterior beams is neglected, the center 


moment is i x be = re. The moment at the midpoint of each ex- 
terior beam due to the reaction F is x x E = re: The sum of the 


PL 


moments across Section A-A is2 X PE + FE + oR which is the 


moment produced at the midpoint of a simple beam by a load P at 
the center. The same relationship holds for a section normal to 
Section A-A. If the interior beams are replaced by a slab, it follows 
that the sum of the moment in the slab and the moments in the 
supporting beams at any section must equal the moment at that 
section produced by one-way action. Similarly, flat-slab and flat- 
plate floors must be designed to carry the total load in both directions. 


Fig. 4. Dead weight of floors may be reduced by using paper tubes, 
which displace concrete near the neutral axis of the slab. 


Fig. 3. Concrete masonry units serve as filler block for this cast-in-place 
joist floor. The underside of the floor has a smooth surface for direct 
application of ceiling finishes. 


when one-way action is assumed. The percentages are 
given for various values of r, the ratio of the distance 
between inflection points in each of the two directions. 
A maximum decrease of 25 per cent of positive-moment 
reinforcement is permissible in the quarter panels ad- 
jacent to a continuous edge. 

In Method 2, coefficients for determining moment in 
a middle strip (see Fig. 5) are given for panels with various 
combinations of continuous and discontinuous edges and 
for certain values of m, the ratio of short to long span. 
Moments in column strips are taken as two-thirds of 
those in the middle strip. Loads on supporting beams may 
be assumed to be the dead and live loads within the area 
of the adjacent panels bounded by 45-deg. lines from the 
columns and by the median lines parallel to the long side. 
In the design of two-way floor systems the effective depth 
to the steel in one direction is less than in the other, 
since one layer of reinforcement is necessarily on top 
of the other. Because of the more complicated arrange- 
ment of reinforcement in two-way systems, it is generally 
advisable to indicate placing procedures on the working 
drawings. 

Two-way solid slabs are economical for medium to heavy 
loads on spans up to about 30 ft. and are highly efficient 
in carrying machinery and other concentrated loads. This 
type of floor presents a smooth undersurface to which 
paint may be applied directly. 

Often it is desirable to use domes or block fillers to 
decrease the dead weight of two-way floors that support 
uniform loads. Domes for forming recesses in the floor 
are square with sloping sides to facilitate removal. Like 
pans used for one-way concrete joist floors, domes are 
available in various widths and depths. The width of the 
two-way “ribs” is controlled by design requirements but 


should not be less than 4 in., as specified by the ACI Code. 


SUPPORTING MEMBERS 


Both one-way and two-way floor systems carry loads to 
beams, which in turn transmit the load either directly to 
columns, or to girders and then to columns. Although the 


Fig. 5. Two-way solid slabs are especially suitable for resisting con- 
centrated loads. For convenience in design, two-way systems generally 
are considered to consist of middle and column strips, as shown. 


27ST) Ge TES Pa 


determination of beam dimensions depends to a large ex- 
tent on the requirements of moments and shears, the 
designer has considerable latitude in selecting widths and 
depths. An increase in beam depth results in a decrease in 
reinforcement to resist a given moment, whereas an in- 
crease in width results in a shorter span for the slab and 
consequently in lower moments and shears in the slab. 
Less beam depth and greater width lead to a reduction in 
story height and enclosed volume, thereby lowering the 
total cost of walls and vertical piping as well as the cost 
of heating and ventilating equipment. For certain con- 
ditions a wide, shallow beam, called a slab band, is more 
economical than a conventionally shaped beam, even 
though more reinforcement is required in the beam itself. 
Slab-band construction is shown in Fig. 8. 

When panels vary in size, or when panel sizes are 
similar but live loads vary, different beam strengths are 
required. It is generally more economical to vary strengths 
with changes in reinforcement than to adjust beam sizes. 
In any case, beam width should be kept constant so that 
form panels for the slab are the same size. The use of 
actual rather than nominal lumber dimensions reduces 
construction costs because there is less ripping of form 
material. 


FLAT-SLAB SYSTEMS 


The term ‘“‘flat slab” is usually associated with a girder- 
less floor having drop panels and column capitals. Drop 
panels, or thickened portions of the slabs, are formed 
at columns to provide increased cross-sectional area and 
depth to resist negative moments and shears. Column 
capitals, or flared haunches at the tops of columns, are 
used to reduce the slab span; as a result, moments and 
shears are also decreased. Flat slabs are well suited to 
carry either heavy or light live loads and they are also 
highly efficient in supporting concentrated loads. A typical 
flat-slab floor is illustrated in Fig. 9. 

For light live loads, the shears and negative moments 
may be such that drop panels or column capitals are not 
required. Girderless floors without drop panels or column 
capitals are commonly referred to as flat-plate floors. The 
simple formwork required for this type of floor offers 
obvious economy. Figs. 10 and 11 show the use of flat- 
plate floors in apartment buildings. 

In some cases negative moment can be satisfied without 
drop panels or column capitals but shear may be excessive. 
To incréase shear capacity without the use of drop panels, 
special shearhead reinforcement, which has the same 
function as stirrups in beams, is often used. 

Moments and shears in both the flat-slab and flat-plate 
floors may be determined by an analysis of the structure 
as a continuous frame or, within certain limitations as to 
continuity and dimensions, may be determined at critical 
sections by the use of specified coefficients as given in the 
ACI Code. 

Filler block or domes similar to those used in two-way 
floors to produce ribs or joists in two directions may be 
employed in flat slabs or flat plates to reduce dead weight. 


Fig. 9. Flat-slab floors support both heavy uniform loads and large 
concentrated loads efficiently. For a given story height they provide 


maximum clear-ceiling height with few obstructions. 


Fig. 6. The action of a one-way floor is typified by this framework, 
which has a high ratio of long to short span. 


Fig. 7. The action of a two-way floor system may be compared to that 
of a frame in which the ratio of long to short span is 2 to 1 or less. 


Fig. 8. In a large multistory housing project such as this, the lower 
construction cost resulting from reduced floor-to-floor height—made pos- 
sible with a wide shallow beam often called a slab band—produces a 
marked saving. The floor slab is a one-way system. 


(The domed or coffered floor slab is often referred to as a 
waffle slab.) Such construction may be used in the center 
portion of flat-slab floor panels, as shown in Fig. 12. In 
flat-plate panels a solid slab over the columns is retained, 
as shown in Fig. 13, to provide adequate shear and 
moment resistance. 

It is sometimes difficult to furnish sufficient resistance 
to lateral loads in the lower floors of tall buildings of 
flat-plate construction by means of the slab only. An ex- 
cellent solution to this problem is the use of shear walls, 
sometimes called crosswalls. These walls relieve the floors 
and columns of the necessity of resisting lateral loads and, 
in addition, they are useful architecturally. If they are 
included in a tall building less material is required in the 
floors and columns and, as a result, a more economical 
design may be achieved. 


MODIFICATIONS TO THE BASIC 
FLOOR SYSTEMS 


Although this booklet is primarily concerned with concrete 
floor systems that are cast in place, it is also important to 
consider the application of precast concrete to floor con- 
struction. Precast concrete construction permits excel- 
lent control of concrete quality and generally allows 


higher production efficiency and simpler, mace rapid Fig. 10. Flat-plate floor construction requires only the simplest form. 
work because all interior beams are eliminated. Since the formwork t 


building erection. ; simple the framework is rapidly built—an important consideration in 
Almost any of the floors that have been described may multistory apartment buildings. | 


be precast. For example, precast concrete planks and 
channel slabs used in floors are precast one-way systems; 
the planks are similar to solid slabs and the channel 
slabs are comparable in function to joist floors. One-way 
precast systems are particularly economical for light live 
loads, such as in roofs. 

In the type of precast flat-plate floor shown in Fig. 14, 
the floor and roof slabs are cast at ground level, one on 
top of another. After the concrete has attained sufficient 
strength, the slabs are raised to their final elevations by 
means of jacks set on the columns. Except for simple 
edge forms all formwork is eliminated. 

Most of the various floor systems can be prestressed. 
Prestressing produces homogeneous action of the concrete 
and increases the stiffness of the floor. Homogeneity is 
achieved by imposing on each section of the floor or floor 
elements a compressive prestress force greater than the 


eric Sino by design loads. : F Fig. 11. The absence of projections below a flat-plate floor allows com 
e tec miguce of prestressing can be applied to either plete architectural freedom in planning room layouts. Paint may b 
precast or cast-in-place systems. Prestressing is best applied directly to the underside of the slab. 


suited to floors that are lightened with joist construction 
or with hollow cores. The use of these floors rather than 2 
of solid slabs reduces not only dead weight, at little sacri- 


| 


Fig. ‘12. Flat-slab floors of waffle construction, here formed with 
plastic pans, are solid only over the columns. Reduced dead weight 
permits smaller columns and footings. 


fice in strength, but also the amount of prestressing steel 
required. 

Lightweight concrete is sometimes used to reduce dead 
weight. This will result in reduced column and footing 
sizes and may effect an overall economy. 


For almost any set of conditions one of the various 
floor systems described in this section will provide an 
economical floor. In addition to these basic types of floors 
many variations are being designed and constructed that 
serve floor requirements satisfactorily. 


Fig. 13. A coffered concrete ceiling, untreated except for painting, 
gives this waiting room a distinctive appearance. 


Fig. 14. The flat-plate slabs shown here are precast on the floor, one 
on top of another, and then lifted to their proper elevations by jacks. 


Selection of Most Economical Floor System 


Although there may be several designs of concrete floors 
that are suitable, maximum economy can be achieved only 
by careful study of all systems that satisfy the given 
conditions. The magnitude and distribution of live load 
together with building requirements for column locations 
will usually reduce the number of types to be considered 
to three or four. Moreover, since engineering experience 
may lead to the elimination of one or two types, a floor 
system may occasionally be selected without further con- 
sideration. In general, however, final selection of a suit- 
able floor system should be based on preliminary designs 
and cost studies. As an aid in comparing the various floor 
systems, seven typical designs of a floor panel are pre- 
sented in the last section. The panel chosen for these 
designs is an interior panel in the longitudinal direction 
and an exterior panel in the transverse direction, since in 
most buildings there are more panels of this type than 
interior or corner panels. 

Selected spans include as wide a range as _ possible; 


superimposed loads represent the usual upper and lower 
loading limits for each type of floor. Although spans of 
25 ft. are generally excessive for flat-plate construction, a 
25x 25-ft. panel is illustrated so that interpolation may be 
made for panel sizes between 20x20 and 25x25 ft. 
Similarly, a 20x 20-ft. panel of the waffle-type flat plate is 
given to permit panel spans of 23 and 24 ft. to be inter- 
polated, these sizes representing the approximate lower 
economical limit. 

Column sizes given in the examples for flat-plate floors 
are considered minimum for supporting two floors and a 
roof. If larger columns are used the designs are adequate 
but the shearhead reinforcement can be decreased. 
Although moments in a flat-plate panel are a function of 
column sizes, the change in moment due to a change in 
column size is small. For example, if the column shown 
for the 15x 15-ft. flat-plate floor panel supporting a super- 
imposed load of 50 psf is increased from 12x12 in. to 
15x15 in., moments are decreased by only 24 per cent. 


7 


In using the tables to compare various floor systems, it 
must be remembered that the percentage of each beam to 
be included in a panel depends on the size of the building. 
If a building with a one-way, solid-slab floor system, as 
shown on pages 12 and 13, is 7 panels wide and 10 panels 
long, there are 6 longitudinal beams, exclusive of spandrel 
beams, in the 7-panel width; therefore, 6/7 of a longitudi- 
nal beam should be included in each panel. In the 10-panel 
length there are 19 transverse beams and 19/10 of a 
transverse beam should be included in each panel. How- 
ever, for a building of such size there is little error if its 
dimensions are considered infinite and panel quantities 
include one longitudinal and two transverse beams. 

Quantities for square panels other than those listed 
may be estimated accurately by interpolation. In fact, 
values for rectangular panels may be estimated satisfac- 
torily by substituting a square panel of the same area. To 
illustrate this, consider the two-way solid slab shown in 
Fig. 15 for which the accompanying table gives both inter- 
polated and actual quantities. This panel is 20x25 ft. and 
is designed for 100-psf superimposed load. Its total area 
of 500 sq.ft. is equivalent to that of a 22.4-ft. square 
panel. The dimensions of this equivalent square panel are 
not important to the problem since interpolation should 
be based on area. Quantities given with Fig. 15 for the 
300-sq.ft. panel are equal to the sum of the quantities for 
the 20x20-ft. panel (see the two-way, solid-slab design, 
page 19) and of the proportionate difference, (500 — 400) 
+ (625 — 400) or 0.444, between quantities for the 20x 20- 
ft. and 25x25-ft. panels. For example, to interpolate for 
the area of slab formwork in total units per 20x25-ft. 
panel, multiply 0.444 by 198, the difference between the 
values of 351 and 549 taken directly from the tables of 
the two-way, solid-slab design for 20x 20-ft. and 25x 25-ft. 
panels. The product 0.444 X 198 = 88 added to the quan- 
tity 351 for the 20x 20-ft. panel gives 439 sq.ft. per panel. 

Because an equivalent square panel is assumed when 
interpolating for rectangular panels, formwork quantities 
for individual beams will not be comparable with actual 
values. However, total form quantities including all beams 
do compare favorably. 

An inspection of reinforcement in the slab and beams 
shows variations between interpolated and actual values. 
Slab reinforcement for the actual case is slightly less than 
for the equivalent square panel. Longitudinal beam rein- 
forcement is greater for the actual panel since the beam 
has a greater span and carries a larger portion of the load 
than the similar beam in the equivalent square panel. 
In like manner the actual transverse beam has less rein- 
forcement than the theoretical one. However, total slab 
and beam reinforcement in each panel compares favorably. 

The preceding example leads to the conclusion that a 
certain amount of material is required to support a uni- 
form load on a given area regardless of the dimensions of 
the area. This statement is sufficiently accurate as long as 
dimensions are not unreasonably out of proportion. For 
example, quantities for a 15x 40-ft. floor panel with a one- 
way slab are not comparable with those for an equivalent 


square panel of 600 sq.ft. A good rule of thumb in using 


8 


a 
fs 
© 
i 


& 
& 
ca 
Ix 
res) 


10-*2u 


9 


ie ae aN : 
ees, ae AP Obig WAS, ANTES Saabs gore i iN 
Interpolated quantities Actual quantities _ 
Reinforce-| Forms | Concrete | Reinforce-| Form 
atts ment(|b.) | (sq.ft.) (cu.ft.) | ment (Ib.) (sq.ft. 
tae Total me Total re Total ae Total ysl Total}! 
ft Ett; fe, punts sq.ft. units sq.ft. units} 

230 | 0.46 | 1152 | 2.30 | 439 

48 | 0.10} 463}0.93} 98 

28} 0.05] 28210.56} 65 


306 | 0.61 | 1897 | 3.79 


| work totals include beam forms only. 


7 OFT ER a REA TI 


Fig. 15. Comparison between actual and interpolated quantities in a | 
rectangular two-way, solid-slab floor in which the span ratio is less 
than 5 to 3, the limiting ratio above which interpolation is not reliable. 


Fig. 16. Comparison between actual and interpolated quantities in a 
rectangular one-way, solid-slab floor in which the span ratio is 5 to 3. 


Concrete | Reinforce- 


Forms 
(cu.ft.) | ment(lb.)| (sq. 
Total | UM'S) Total 
units att units 
75 
Long.beam 


280 | 0.75} 312 
178 | 0.47} 46 
| Trans.beam 217 10.58} 74 


Total* | 180 | 0.48 | 952 | 2.54 | 156 | 0.42 | 193 0.51 892 } 2.381 194 


| Slab 125 


*Totals include one longitudinal beam and two transverse beams. Fo 
| work totals include beam forms only. 


the tables to determine quantities for rectangular panels 
is that the ratio of long span to short span should not 
exceed 5 to 3. Fig. 16 shows a one-way slab floor panel in 
which the long span is two-thirds greater than the short 
span. A panel with 375 sq.ft. lies between a 15x15-ft. and 
a 20x20-ft. panel. The table of Fig. 16 gives actual and 
interpolated values and again total quantities are com- 
parable although the discrepancy is greater than for the 
20x25-ft. panel of Fig. 15. 

Interpolation also may be made when superimposed 
loads vary from those given in the tables. Linear extrapola- 
tion may be made for spans beyond the range of the tables 
up to approximately 30 ft. Extrapolated quantities will be 
comparable although somewhat less than actual values. 

To outline the procedure for selecting a floor system, 
a study is made of a warehouse with the following require- 
ments: a typical panel is 23x23 ft. and the total super- 
imposed load is 200 psf; the warehouse is four stories 
high and requires no ducts for heating or ventilating; no 
ceiling finish is necessary but painting is desirable to 
improve illumination; the building is three panels wide 
and nine panels long. 

From the given requirements it appears that three floor 
systems, the one-way solid slab, the two-way solid slab 
and the flat slab, should be investigated. Interpolation is 
made for a panel area of 529 sq.ft., for which the propor- 
tionate difference between areas of the 20x20-ft. and 
25x25-ft. panels is 0.57. The results of the interpolation 


Item 


Forms (slab) 


Forms (long. beam) 
Forms (trans, beam) 


Beam forms total* 


Concrete (slab) 
Concrete (long. beam) 
Concrete (trans. beam) 


Concrete total* 


Reinforcement (slab) 3.50 

Reinforcement (long. beam) E 1.00 

Reinforcement (trans. beam) 1.20 
Reinforcement total* 


Total cost per sq.ft. 1.72 


*Totals include 2/3 of a longitudinal beam and 17/9 of a transverse beam for 
the one-way system and 8/9 of a transverse beam for the two-way system. 


Note: The unit prices are only approximate and must not be used in any actual 
cost comparison. Cost data obtained locally from published records or contractors 
should be substituted to obtain more accurate comparisons. 


Fig. 17. Summary of unit quantities and costs for floor systems suitable 
for a typical 23 x 23-ft. warehouse panel. 


are given in Fig. 17. The costs show that a flat slab is the 
most economical floor. The unit prices shown in Fig. 17 
are only approximate and must not be used in any actual 
cost comparison. Cost data obtained locally from published 
records or contractors should be substituted to obtain 
more accurate comparisons. 


Special Design Details 


In addition to structural analysis, a floor design includes 
_ consideration of details such as the position of reinforce- 


ment around openings and in sections that may be 


_ affected by forces due to shrinkage or temperature changes. 


Fig. 18 is not a typical floor layout but is intended to 


illustrate some of the details that ordinarily need special 
attention. Details are numbered on this layout for separate 
discussion. 


Floor reinforcement, besides being provided for moment 


-and shear requirements, is also used to resist forces 
resulting from volume changes. The ACI Code specifies 
a minimum reinforcement of 0.2 per cent of the cross- 


sectional area based on effective depth in floors reinforced 
with deformed bars and a minimum reinforcement of 0.18 
per cent when welded wire fabric is used. In roofs the 
respective values are increased to 0.25 and 0.22 per cent. 

In Fig. 18 the volume-change forces due to shrinkage 
or temperature changes acting over the full width of the 
floor are concentrated at a narrow section (see details 


1 and 8) that is only about one-fourth the width of the 
full slab. A desirable solution to this problem is to sepa- 
rate the two floor areas with an expansion joint. If it 
is necessary to make the two areas integral, as in this 
layout, a control joint and additional reinforcement should 
be provided. The amount of reinforcement to be added 
depends on the arrangement of the floor. In this case 
twice the amount of minimum volume-change reinforce- 
ment is considered sufficient for the concentration of 
these forces. 

The additional bars shown in Detail 18-1 must be ex- 
tended a sufficient distance beyond the narrow section to 
resist the tensile forces due to shrinkage as they spread 
out; extra bars should be placed in adjacent panels to 
assist in distributing the forces transversely. It is always 
good practice to cut off no more than half of the bars at 
a section to prevent the total transfer of tensile forces 
from the reinforcement to the concrete at that section. 
This is especially true of bending-moment reinforcement 


9 


Fig. 18. A floor layout that includes eight 
special design details. 


when the analysis indicates that either positive or negative 
moment no longer exists or is greatly reduced beyond the 
section. 

A similar need for additional reinforcement is shown in 
detail 8, Fig. 18. Openings in a floor for stairs, elevators 
and pipe chases produce a weakened plane that should 
have adequate volume-change reinforcement. As in Detail 
18-1 the reinforcement should extend into the slab far 
enough to allow distribution of the forces, and cutoff 
points should preferably be staggered. 

Detail 2 of Fig. 18 indicates another type of weakened 
plane caused by conduits or pipes embedded in the slab. 
An important advantage of concrete floors is that con- 
duits may be placed in the slab with almost complete free- 
dom of location at little additional expense. However, it 
is advisable to limit the size and number of these facilities 
at any section in a floor so that the cross-sectional area 
in the plane of the axis of the conduit is not decreased by 
more than one-third. This condition is illustrated in Detail 
18-2. If small pipe or conduit is to be used in a concrete 
joist floor a slab no less than 3 in. thick is recommended. 

Small openings may be built in concrete floors without 
additional beams framing the opening. Reinforcement 
may be spread to bypass the hole, as indicated at the left 
portion of Detail 18-3, or the reinforcement may be 
terminated at the opening and additional bars added at 
the sides equivalent to the interrupted steel area, as indi- 
cated in the right portion of Detail 18-3. Studies of slabs 
and deep girders show that the stress effects created by 
openings extend out a distance equal to the width of the 
opening; thus the bars need to be spread only as far as 
this distance from the opening. The redistribution of 
stresses around an opening induces a transverse moment 
in the vicinity that should be resisted by short bars per- 
pendicular to the main reinforcement as shown in De- 
tail 18-3. 

At a corner (detail 4 of Fig. 18) a local negative mo- 
ment exists in the slab in the diagonal direction. To pro- 
vide for this moment, top bars should be placed in the 
slab as indicated in Detail 18-4. 

Although slabs in exterior panels are generally con- 
sidered to be simply supported at the outer edges, negative 
moment exists along these edges because of the torsional 
restraint of the rectangular spandrel beams. The magni- 
tude of this restraint depends on the cross-section and 
span of each spandrel. For example, in Detail 18-5(a), 
the negative moment in the slab at the midspan of the 
spandrel is approximately 80 per cent of the fixed-end 
slab moment when infinitely rigid columns and a span of 
20 ft. for the spandrel and 10 ft. for the 4-in. slab are 
assumed. In Detail 18-5(b) the same conditions are as- 
sumed except that the spandrel dimensions are reduced 
from 9/2x46 in. to 54x18 in. As a result the negative 
slab moments are only 20 per cent of the fixed-end mo- 
ment. When column flexibility is considered, these per- 
centages will be modified according to the relative stiff- 
nesses of columns and of the entire slab between centers 
of bays. 


Frequently overlooked in one-way slab design are the 


10 


Detail 18-1 


Detail 18-2 


Detail 18-3 


Cut off alternate bars — 


Half Section- Type I 


Ve h Maximum 


Half Section- Type I 


Negative moment= Negative moment= 
80 % of fixed-end 20 % of fixed-end 
moment moment. 


pof short span 


phinimam reinforcement 
0.005 bd (AC! Code) 


Usually FL _ 


Detail 18-4 


Detail 18-5 


Detail 18-6 


Detail 18-7 


negative moments that exist over the short beams normal 
to the direction of the main reinforcement. Such a con- 
dition is indicated in detail 6 of Fig. 18. This negative 
moment is constant when the ratio of long to short span 
is greater than 5 to 3. At interior supports where the edge 
of the slab may be considered fixed, the negative moment 
in the slab at midpoint of the short beam is 0.0571wL?, 
where L is the span in the short direction. The amount of 
restraint at the spandrel beam is determined in a manner 
similar to that described for Detail 18-5. Reinforcement 
provided for the moments should extend at least a dis- 
tance equal to L/2 into the slab, as shown in Detail 18-6. 

Detail 7 of Fig. 18 illustrates a floor beam framing into 
a spandrel beam. Here again it is common practice to 
assume a simple support in the analysis. However, the 
ACI Code specifies a minimum amount of negative rein- 
forcement at the outer end of all members built integrally 
with their supports. If a beam intersects a spandrel only 
a short distance from a column it will be necessary to 
provide more than the minimum negative reinforcement. 

Negative bending moment at the discontinuous end of 
a beam due to support restraint usually varies between 
1/24 and 1/16 wL?. Based on these moments, the point 
of inflection falls between 1/9 and 1/6 of the span. Since 
reinforcing bars are customarily bent up at 1/7 L, as 
shown in Detail 18-7, it is possible for negative moment 
to exist beyond the region reinforced by bent-up bars. 
For this reason, it is good practice to provide straight top 
bars at the discontinuous end of a beam even though the 
bent-up bars satisfy code requirements. 

Construction joints are often located at the discretion 
of the construction superintendent. However, these joints 
should be shown on the plans when it is desirable to avoid 
the possibility that they may open. Joints located in areas 
of positive moment, such as near midspan, have the least 
opportunity for opening and showing a crack in the top 
surface of the slab. As an added precaution against such 
cracks, short bars may be placed near the top of the slab 
across the joint. In cases where leakage must be prevented 
a cut 4 in. deep may be made along the joint in the top 
surface of the slab and calked. 

This discussion indicates that a general appraisal of a 
floor under design is often as important as the structural 
analysis and the selection of reinforcement. Design judg- 
ment based on experience will anticipate the trouble 
spots, provide for the difficulties and thus result in a 
sounder, more satisfactory floor design. 


1] 


Designs of Typical Floor Systems 


In this eight-page section typical designs for seven differ- 
ent floor systems are given. Variations in spans and super- 
imposed loads are included to cover the full range of use 
normally associated with each system. Superimposed 
load, the sum of all loads except dead weight of the floor 
itself, includes loads due to partitions, floor and ceiling 
finishes, and live load. 

All floors are designed to meet requirements of the ACI 
Code. Designs are based on a concrete stress of f’¢ = 3,000 
psi, a steel stress of fs = 20,000 psi and the use of 
A305* reinforcing bars. 

Accompanying tables give material quantities for form- 
work, concrete and reinforcement without allowance for 
waste or breakage. Quantities are given in terms of total 
units and units per square foot of panel; total units for 
slab quantities are given per panel while total beam quan- 
tities are given per beam. 

In the tables beams parallel to the spandrel beams are 
designated longitudinal beams while those perpendicular 
to this direction are designated transverse beams. Span- 
drel-beam quantities are not given since spandrel sizes 
often depend on architectural requirements. 

Column capitals are considered as part of the columns 
and are not included in the quantities. 

Quantities are determined in the following manner: 

1. Area of pan forms = (panel length — beam width 

— 6in.) X panel width. 


ONE-WAY SOLID SLABS 


2. Area of slab forms equals the area inside beams for 
slab and beam systems, and the area of the panel 
itself for flat-slab systems. 

3. Area of beam forms = (beam width + 2 X depth 
of beam stem) X (beam length — beam width). 


4. Volume of slab concrete = (panel area X slab thick- | 


ness) — volume of pan forms or filler block. 

5. Volume of beam concrete = cross-sectional area of 

beam stem X (beam length — beam width). 

In the floor plans cutoff and bend-up points for rein- 
forcement are shown as recommended in the Manual of 
Standard Practice for Detailing Reinforced Concrete Struc- 
tures (ACI 315-51) except in the case of flat-plate floors 


of the solid and waffle types in which straight bars have a — 


length equal to the panel length minus 1 ft. in column 
strips and 0.7 of the panel length in middle strips. The 
symbol (E) after straight bars indicates an embedment 
of 20 diameters past the column face. Hooks shown at 


discontinuous edges of slabs also indicate 20-diameters — 


embedment. 


*Specifications for Minimum Requirements for the Deforma- 


tions of Deformed Steel Bars for Concrete Reinforcement (ASTM ~ 


Designation: A305). 


50-PSF SUPERIMPOSED LOAD 


ee te 


a? : 
we ; 
MS ae ) { 
lt iv 
ls 
BS 
. | | 
eis. 
Formwork (sq.ft) 
15x15 20x20 25x25 
Total ae Total a r_| Lotal p ee gi 
units sq.ft. units sq.ft. units sq.ft. units sq.ft. sq.ft. sq.ft. 
Slab 75 }.0.33 | 1332) 0:33 1208 |) 0:33.01 193% 4°0.86 C400 ete POO Re 77a a 529 | 0.85 3 
Long. beam 10 | 0.05 25 | 0.06 47 | 0.08 | 116 | 0.52 | 308 | 0.77 | 597 | 0.96 101 | 0.16 @ 
Trans. beam 6 | 0.03 18 | 0.04 32 | 0.05 45 | 0.20 | 167 | 0.42 | 362 | 0.58 80 | 0.13 
& 
Note: 1. In each panel the three transverse beams are identical. : 
Zs sa reinforcement is shown in the left half and reinforcement perpendicular to the main steel is shown in the right half of each — 
panel. 4 
M 


12 


ONE-WAY SOLID SLABS 


100-PSF SUPERIMPOSED LOAD 


__15+0" Square 


4-in. Slab 


Ly 
"7 Bt +2-"6 Sie) 
Teur 


20-0" Square 


(as 
ie. 
142 UF 


— jin 
++ 
ae) 


Reinforcement (Ib.) 


20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 
Item Tot ius Total Units Tara E Total vals Total ae Total ait Total ee Ne 
units att units sate units a ft units units a a units a a units on a units ae ft. 
Slab 133 | 0.33 | 208 | 0.33 | 216 | 0.96 | 461 | 1.15 | 1200 } 1.92 a 0.82 | 328 | 0.82 } 529 | 0.85 
Long. beam -29 | 0.07 56 | 0.09 | 163 | 0.72 | 395 | 0.99 748 | 1.20 0.18 70 | 0.18 | 113 } 0.18 
Trans. beam 22 |} 0.05 38 | 0.06 86 | 0.38 | 224 | 0.56 389 | 0.62 | 2 0.14 58 | 0.14 92 | 0.15 


200-PSF SUPERIMPOSED LOAD 


__18'=0" Square | 


*“7St(E) 
=46 


Concrete (cu.ft.) 


fg 2070 oguare:) a | 


Reinforcement (Ib.) 


25'-O" Square 


4-in. Slab 


“I= as Top Each End) 
18-72 


[1] eas jon 


Formwork (sq.ft.) 


v, 2570" Square) 


15x15 20x20 25x25 15x15 20x20 25x25 
Item Total ae Total Units Total a Total Units Total ea ea 
units sq.ft units sq.ft. units sq.ft. Ble sq.ft. units sq.ft. sq.ft. 
Slab 78 G33 17 133%-) 0:33} 261 91 0.42 | 2587) 114 | 764-7 1.91 2.29 
Long. beam 16 0.07 39 | 0.10 79 | 0.13 | 224 | 1.00 | 496 | 1.24 eS 
Trans. beam 12 0.05 29 | 0.07 52 | 0.08 | 129 | 0.57 | 286 | 0.71 0.95 


Note: 1. In each panel the three transverse beams are identical. 
2. Main reinforcement is shown in the left half and reinforcement perpendicular to the main steel is shown in the right half of each 


panel. 


13 


sea ESE eee ots eet Eo 


ONE-WAY JOISTS—20-IN. METAL PANS J 


—50-PSF SUPERIMPOSED LOAD 


ee the 20-0" Square _ 7 hea | 25-0" Square | 


lo" 25. 
12.5 Joists per panel | 


Per Joist i-#6 


\ ki oo ie ee 
. 


25x25 20x20 | 26x25 —=«|~SCsdoxTS ~—=«Y;S20x20— |S 


Item Total it Total Uni Units Total Units Bite Total pe Total Units Units - 
units amit units saft sat units ante units unt units ‘att units | 
Slab TG Wi eeie 3) ae) | a 43 | 208 | 0.92 | 479 | 1.20 | 1056 | 1.69 | 210 | 0.93 | 375 | 0.94 | 590 
Long. beam 5 10,02 13 | 0.03 26 04 | 100 | 0.44 | 244 | 0.61 | 590 | 0.94 24 10.11 44/011 72 
Pans 210 | 0.93 | 375 | 0.94 | 588 


100-PSF SUPERIMPOSED LOAD 


: | ___25+0" Square l 


Ts" arr 2-"o ste 
IB UL j 


Concrete (cu.ft.) Reinforcement (Ib.) 


Formwork (sq.ft. 
20x20 25x25 1 inte 15K Ome meno xe 15x15 20x20 
Item Total Units | topqy | Units Total | Units Units | rotay | Units | Total 
units | Pe" | units units | Per i per | units | Per i 
sq.ft. sq.ft. ite sq.ft. sq.ft. 
Slab 11s) 0.348 (155 309 | 1.37 | 677 | 1.69 | 1386 | 2.22 | 210 | 0.93 
Long. beam 9 | 0.04 20 127, 0.567 1283 10.717 2 8it 120 32 | 0.14 56 


Pans 210 | 0.93 | 375 | 0.94 


Note: 1. 6” + 2%4" indicates a pan 6 in. deep and a slab 24 in. thick. 


14, 


ONE-WAY JOISTS—16-IN. FILLER BLOCK 
50-PSF SUPERIMPOSED LOAD 


15-0: Square | 20-0" Square 25'-0" Square 


4+ 2x 21 (R) 6+2 x21 (R) 8+ 2x21 (R) 
86 Joists per panel 11.4 Joists per panel 14.3 Joists per panel 


Per Joists |-#7 


iy 
* 
i 
ra 
is) 
oe 
bi) 
a 


i7-#2 


Eo Bry [7 SLE) FT : eS. 12-* Bt + 2-*8 SLE. 
10-*2 7 14-*317 


Reinforcement (Ib.) Formwork (sq. ft.) Masonry units (no.) 
20x20 25x25 15x15 20x20 25x25 
Units Total Units Total Units Total nits Total nits 
Pet units | Pet units | Pe units | PE" lunits Pe! 
sq.ft. sq.ft. sq.ft. q.ft. sq.ft 


we 519 0.83 


Concrete (cu. ft.) 
15x15 20x20 25x25 15x15 20x20 25x25 15x15 


Item Total Units Total pe Total se Total Units Total Units Total pals Total ae Total 

units sq.ft. units itt units Gat units sq.ft. units La units Hit units ne units’ 

67 | 0.30} 140 | 0.35 | 248 | 0.40 | 292 | 1.30 | 573 | 1.43 }1439 | 2.30 | 210 | 0.93 | 375 | 0.94 | 590 |0.94 | 183 {0.81 | 328 
55 10.14 | 84 10.13 


Siab 
Long. beam 8 10.041 2010.05! 36 10.06 | 114 10.51 1279 10.70 1582 10.93 1 30 10.13 


100-PSF SUPERIMPOSED LOAD 


I5'~O" Square 20-0" Square 25-0" Square l 


6+2x 21(R) 8+2x 2/(R) 10 t 2x 21(R) 
8.6 Joists per panel 11.4 Joists per panel 14.3 Joists per panel 


Per Joist 
Per Joist ¢ j-#7 


17-*2 28-*2 


Masonry units (no.) 
15x15 20x20 25x25 


Reinforcement (Ib.) Formwork (sq. ft.) 


Concrete (cu. ft.) 
25x25 15x15 20x20 25x25 


20x20 29x25 15x15 20x20 


15x15 
item otal|4"'tS| Total ith Total es Total ae Total vote Total ee Total see Total ee Total we Total rae otal an otal o 
units sq.ft. units units sq.ft. units sq.ft. units sq.ft. sq.ft. units sq.ft. units sq.ft. units sq.ft. units aft. units aft. nits q.ft. 
Slab 79 }0.35 | 161 |0.40 } 283 10.45 | 295 | 1.31 | 740 }1.85 1575} 2.52 | 210 |0.93 | 375 | 0.94 | 585 |0.94 | 183 | 0.81 | 328 |0.82 | 515 | 0.82 
Long. beam 9 10.04 | 23 10.06} 49 10.08 1125 10.55 1350 10.88 | 702 11.12 | 33 10.14 | 61 10.15 1100 10.16 


Note: 1. 4 + 2 X 21(R) indicates a 4-in. block, a 2-in. slab and a 21-in. joist spacing. 
2. (R) indicates regular block and (S), if shown, indicates soffit block. 


15 


FLAT PLATES 


50-PSF SUPERIMPOSED LOAD 


Concrete (cu. ft.) Reinforcement (Ib.) 


15x15 20x20 25x25 15x15 20x20 25x25 
Item Total Units Total Units Total ee Total Units Total Units Total Hi 
units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. 


Slab 94°} 0.42.| 250. ] 0.62 | 521] 0.83) 419) 186i] 9967)" 2.49") 20454" 3:27 


100-PSF SUPERIMPOSED LOAD 


20-0" Square 25-0" Square 


PLN BRS 
Band width 
ses 


Concrete (cu. ft.) Reinforcement (Ib.) Formwork (sq. ft.) 
15x15 20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 
Item Total gis Total Units Total pu Total Units Total Units Total sa Total Units Total Units Total Be 
units sq.ft units sq.ft. units ane units sq.ft. units sq.ft. units eat units sq.ft. units sq.ft. units nit 
Slab TAZ 0:50) ie 283 OTe eon OS ao od PIRATES | ZF) AASV) UAE) | UY) 400 | 1.00 | 625 | 1.00 


Note: 1. Size and spacing of reinforcement in exterior-column strips is the same as in interior-column strips. 
2. Shearhead reinforcement is indicated by A. 8-43 A means eight No. 3 stirrups, two per column face. Exterior columns require half 


the stirrups shown for interior columns. 


16 


FLAT PLATES—WAFFLE CONSTRUCTION 


50-PSF SUPERIMPOSED LOAD 


pei 0 - Os Square: >! 


Concrete (cu.ft.) Reinforcement (Ib.) Formwork (sq.ft.) 
20x20 25x25 30x30 20x20 25x25 30x30 20x20 25x25 30x30 
Item Total it Total Units Total Units Total Units Total Units Total pe Total pee Total ae Total eit 
units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft units sq.ft. units sq.ft. units sq.ft. units sq.ft 
Slab 725190343 O20 2a 5749 0.64 SOT a eel oOZe oi OZo TES: OV mn R400 1.00 | 625 1.00 | 900 1.00 
Pans TesSOn0C4aeeo 55 0.89 1 783 | 0.87 


100-PSF SUPERIMPOSED LOAD 


_20°0" Square 


ss aes 


| ! 
IDOOEEE 


Pot Jehes 


| f i | % AGT af 
4 | iS 
pain | 2 ce ag eres 
ES EL) LASS CHEETA | ms RES i AS 
Concrete (cu.ft.) Reinforcement (\b.) Formwork (sq.ft.) 
20x20 25x25 30x30 20x20 25x25 30x30 20x20 25x25 30x30 
Item Total ae Total Units Total ea Total se Total ae Total ¥h Total st Total pas Total ite 
units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. He sq.ft. units sq.ft. units sq.ft. mnits sq.ft. 
Slab 205 | 0.51 | 398 | 0.64} 686 | 0.76] 927 | 2.32 | 1967} 3.15} 3993] 4.44) 400] 1.00] 625} 1.00] 900 | 1.00 
Pans SOOMMOLCAs MOLI O-Conn 73a} 0:81 


Note: All domes are 20 in. square. 
. Reinforcement in each band is given per joist. 


No. 2 bars are slab reinforcement given per joist. 


SFwN He 


6” + 2)” indicates a dome 6 in. deep and a slab 2) in. thick. 
. Joist widths are as follows: 20-ft. span, 4 in.; 25-ft. span, 5 in.; 30-ft. span, 5/2 in. In the 30-ft. spans six joists in each column strip 


[Sal 


are 6 in. wide. 


Oo 


. Reinforcement per joist in exterior-cotumn strips is the same as in interior-column strips. 
. Shearhead reinforcement is indicated by A. 8-43 A means eight No. 3 stirrups, two per column face. Exterior columns require half 


~ 


the stirrups shown for interior columns. 


FLAT SLABS , 


-100-PSF SUPERIMPOSED LOAD 


Oi! ig@OrON Square 


Item 


Slab 100 | 0.45 | 242 | 0.60 } 445 | 0.71 | 343 | 152 | 852 | 2.13 | 1835 | 2.94 : 409 | 1.02 | 637 


200-PSF SUPERIMPOSED LOAD 


7+ 
Mime at. | 


Concrete (cu.ft.) 
15x15 20x20 25x25 


1270. 


116 | 0.52 | 250 | 0.62 | 501 | 0.80 | 485 | 2.15 3.17 | 2710 | 4.34 | 231 | 1.03 | 409 | 102) 639 


18 


TWO-WAY SOLID SLABS 


100-PSF SUPERIMPOSED LOAD 


fot eae Sousa 20'-0" Square a 


t, 


Seder 


Concrete (cu.ft.) Reinforcement (Ib.) 


-——— 257075 Mare 


Formwork (sq.ft.) 


15x15 20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 
Item Total ae Total ee Total sed Total Total Total ae Total ee Total aa 
units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. sq.ft. 
Slab 75 | 033! le7| 0.42! 3391 0.54| 356| 1.58] 930{/ 2081 1o62| 206] 197| 0.88] 351| 0.88) 549] 0.88 
Long. beam 9 | 0.04| 23| 006] 45| 0.07] 112] 0.50] 239] 0.60) 583] 0.93) 33] 0.15] 61) 015| 94] 0.15 
Trans. beam | 12 | 0.05] 29] 0.07] 54| 0.09] 130] 0.58) 288] 0.72| 625) 1.00] 37| 0.17] 70] 0.18] 105| 0.17 


200-PSF SUPERIMPOSED LOAD 


| 15-0" Square 20'-0" Square | 


: I-"9 Top 
Bi +I-"TBt = 
2u 


/OBt.+ I= 118i 
I- FIOSK(E) 10- 


Ra: 
2- *7Bt +27 51S?! (E. oH 
1-*4 Top Each End 8-21 
aes eal 


| | 


25-0" Square i 
le Tee ‘ 


Slab 75 184 339 5/3 ied: PETS 2435 
Long. beam 14 | 0.06 32} 0.08 59 | 0.10} 137 | 0.60} 334] 0.83} 700 
Trans. beam 17 | 0.08 38 | 0.10 Po NO 2atan 12321 0.07, |) ¢ 400} 1.00) f 5 7838 


per 


Note: 1. Reinforcement is shown for quarter-panel strips adjacent to beams rather than for full column strips. 
2. Longitudinal reinforcement given for the middle strip includes the column strip adjacent to the spandrel. 


25x25 
its Units 
ane sq.ft. 
0.86} 540 
0.18; 109 
0.20} 124} 0.20 


0.86 
0.17 


19 


FORMS 

_ FORK 
AKCHAITECTURKAL 
CONCKETE 


PORTLAND CEMENT ASSOCIATION 


‘ " 
a 
ws 
x mp 7 
* 
ay 
: 
- 
j 
; 
sf 
2 
lo 
n 
P) 
? t 
1 


concrete for permanence 


FOKMS 
FOR 


AKCHITECTURKAL 
CONCKETE 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the devel- 
opment of new or improved products and methods, technical service, promotion and educational effort (including safety 
work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold pro- 
gram of the Association and its varied services to cement users are made possible by the financial support of over 65 
member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of 
all portland cement used in these two countries. A current list of member companies will be furnished on request. 


Copyright 1952 by Portland Cement Association 


PORTLAND CEMENT ASSOCIATION 
33 West Grand Avenue . Chicago 10, Illinois 


Foreword 


‘bss is little information in American literature and not much more in 
foreign publications regarding forms for architectural concrete construction. 
This situation is no doubt due, in part at least, to the familiarity of most con- 
tractors with formwork for structural concrete. The technique and craftsman- 
ship of the form construction involved in the use of concrete as an architectural 
material, however, is quite different from that for structural concrete, al- 
though fundamentally the same principles apply. In order to meet the demand 
for information pertaining strictly to formwork for architectural concrete 
buildings, this booklet has been prepared. Only those phases of form con- 
struction that apply especially to architectural concrete have been included. 
Not every conceivable detail has been shown, but important phases have been 
covered with enough examples and suggestions to enable the careful con- 
tractor, though inexperienced in architectural concrete, to produce a thor- 
oughly satisfactory job. 
PORTLAND CEMENT ASSOCIATION 


Contents 


Section 

Introduction . 

Structural Design 

Mill for Making Forms . 

Erection Accessories. 

Planning the Job 

Detailing: as. 028i es: gt ceed ees 
Kinds and Grades of Lumber and Where Used 
Wood Molds 

Plaster Waste Molds 

Metal Forms and Molds 

Typical Forms aed 
Erecting—Oiling—Stripping 

Estimating 

A Typical Job 


GO NO O30) CO BNI OL Oi ts (Coe ND 


Page 


Fig. 1—Main entrance to Portland Cement Association Laboratories, Skokie, Ill. The pleasing texture, clean 
lines and sharp details are the result of careful form construction and rigid control in proportioning, mixing 


and placing concrete. Carr & Wright, architects; Turner Construction Co., contractor. 


INTRODUCTION 


N an architectural concrete building the concrete has a 
two-fold purpose. Not only does it serve as the struc- 
tural material but it also provides the exterior finish, thus 
becoming the architectural medium. Molded in its final 
position, the concrete permanently records every detail, 
good or bad, of the contact surface of the forms. Conse- 
quently, materials selected for the forms and the degree 
of perfection in the form construction will largely deter- 
mine the architectural effects obtained. 

With the growing use of architectural concrete, con- 
struction technique and craftsmanship have so improved 
and developed that by selection of form material and by 
the manner in which it is used, surface textures and de- 
tails may be obtained which are in keeping with any 


SECTION | 


architectural style. Indeed, the architect has at his dis- 
posal,a range of textures from glass-like smoothness to 
very rugged surfaces. Intricate details as well as very 
simple ones may be formed with plaster waste molds or 
with milled wood forms and these details become an in- 
tegral part of the finished structure. 

Where exposed concrete is the architectural medium, 
the object of the forms is not simply to support the un- 
hardened concrete, but to combine with that function the 
important purpose of giving character to the structure 
through form, texture and detail. Extra care is therefore 
warranted in designing and fabricating the forms to 
achieve the perfection of detail that is so desirable in 
architectural concrete. 


The drawings in this publication are typical designs and should not be used as working drawings. 
They are intended to be helpful in the preparation of complete plans which should be adapted to 
local conditions and should conform with legal requirements. Working drawings should be pre- 
pared and approved by a qualified engineer or architect. 


ee F ish oe 


# 


Fig. 2—The formwork for the California Fruit Growers Exchange, Los Angeles, is an example of uniform spacing of 
studs and wales, even for high walls. Walker & Eisen, architects; Wm. Simpson Construction Co., contractor. 


STRUCTURAL DESIGN 


ORMS must have adequate strength in bending and 
Jie to withstand the pressure of the freshly placed 
concrete. The deflection of sheathing, studs and wales 
must be kept within smaller limits than generally allowed 
on structural work, where appearance is not so important. 

In the design, due consideration must be given to the 
loads or pressures to which the forms are subjected; to 
the allowable working stresses for the materials used; to 
the modulus of elasticity of the material; and to the per- 
missible deflection. 

Experience has shown that certain maximum spacings 
of studs, wales and ties should not be exceeded regard- 
less of computed values. This is not because the forms 
would fail if these spacings were exceeded slightly, but be- 
cause with reuse of material the deflections may increase 
and because the forms cannot be held to a true line if 
the members are spaced too far apart. It is important, 
however, to check the maximum arbitrary spacings to be 
certain they should not be still further reduced if condi- 
tions differ materially from the following: On the assump- 
tion that concrete will be placed at a rate of about 2 ft. 
an hour and the temperature may be 50 deg. F. or slightly 
lower, studs should not be spaced more than 16-in. 
centers when used with l-in. sheathing or 11/16-in. or 
thicker structural grade plywood and not over 12-in. 
centers with %-in. plywood. Wales should not be more 


4 


SECTION 2 


than 24-in. centers and ties having a minimum working 
strength of 3000 Ibs. when fully assembled should be 
spaced not more than 27-in. centers when used with 
double 2x4-in. wales. 


Pressures 


Forms for architectural concrete are usually vertical. 
Therefore, the horizontal pressure exerted by the concrete 
is the load for which they must be designed. There is some 
uncertainty as to the exact pressure exerted by freshly 
placed concrete, but experience, supported by some test 
data, indicates for practical purposes the pressures that 
should be used for safe design. 

The pressure is influenced by the following factors 
which should be taken into account by the designer: 

1. Method of placing concrete, whether by hand or 
by vibration. 

2. Rate of filling the forms. 

3. Temperature of the concrete. 

The consistency and proportions of the mix also affect 
the pressure but evaluation of these factors is difficult 
and, as a rule, they can be neglected within the range of 
mixes used in building construction. Likewise, the size 
and shape of the forms and the amount and disposition 
of reinforcement generally may be neglected. 


High-frequency vibration causes concrete to act as a 
fluid and the fluidity is retained during the vibration 
period.* The full height of concrete under vibration must 
be considered as the head, and the pressure exerted is the 
same as for a liquid having the weight of concrete, which 
may safely be assumed as 145 pcf.** 

When concrete is compacted by hand, the agitation is 
not sufficient to maintain the mass in a fluid condition. 
The pressures exerted are therefore somewhat less than 
the full hydrostatic head. Tests show that, for each rate 
of placing, the pressure increases to a certain maximum 
and then decreases. The more rapid the placing rate, the 
quicker the maximum pressure is attained, because the 
concrete becomes so compacted when it reaches a certain 
depth (variable depending upon rate of placing) that it 
will support additional concrete without exerting addi- 
tional pressure on the forms. This state is reached, when 
placing at a rapid rate, before hardening of the concrete 
has begun; but for slower rates, probably under 2 or 3 ft. 
per hour, the hardening of the concrete combines with 
the compaction to prevent further increase in pressure. 

The temperature of the concrete also has a marked in- 
fluence on the maximum pressure and the elapsed time 
before it is reached. For example, mixtures placed at 
70 deg. F. develop maximum pressures equal to about 75 
per cent of those placed at 50 deg. F. Fig. 3*** shows con- 
servative pressures for concrete placed at rates from 2 to 
6 ft. per hour and at temperatures of 70 deg. and 50 
deg. F. Forms of less depth than the depth at which 
maximum pressure is attained for the different rates of 
placing should be designed to withstand the pressures 
indicated by the full lines. In deep forms, that part below 
the depth of maximum pres- 
sure should be designed for the 
maximum pressureas indicated 
by the change in direction of 


with the same spacing of studs and wales to the top. 
Some saving in material can be made in long, high 
walls by taking advantage of the lower pressure near 
the top, but this is seldom of importance in ordinary 
buildings. 


Allowable Stresses 


Formwork, being temporary, may be designed for 
somewhat higher working stresses than allowed for per- 
manent construction. It is not advisable to go to ex- 
tremes, however, because forms may be overloaded be- 
cause of an unexpected rapid rate of placing or other 
reason, and the result of a form failure is very trouble- 
some to correct. Theoretically, the kind of lumber used 
makes some difference in allowable design stresses, but 
for the kinds generally used, extreme fiber stress of 1800 
psi* and horizontal shear of 200 psi may be used. If the 
higher-strength woods such as Douglas fir and Southern 
pine cannot be obtained, and one of the woods consid- 
erably lower in strength must be used, some adjustment 
should be made in the working stresses. Table 1 gives 
safe working stresses for form design for various kinds 
of lumber. 


Deflection 


Forms must be so designed that the various parts will 
not deflect beyond prescribed limits; otherwise, the fin- 
ished wall will be out of alignment and unsightly bulges 
will mar the appearance. The exact amount of deflection 
permissible depends upon the desired finish and the loca- 


*psi—pounds per square inch. 


the lines of pressure. Generally, 
building forms of such depth 


as to require that the bottom 
part be designed for the maxi- 
mum pressure are constructed 


*L.W. Teller, ““The Effect of Vibra- 
tion on the Pressure of Concrete 


Against Formwork,” Public Roads, 
March 1931, Vol. 12, No. 1, page 
11. Raymond E. Davis and Harmer 
E. Davis, ““Compaction of Concrete 
Through the Use of Vibratory Tam- 
pers,” Journal, American Concrete 
Institute, June 1933, Vol. 4, No. 9, 
page 365. 


Vertical feet below surface of concrete or top of wall 


**pycf—pounds per cubic foot. 


***Reproduced by permission of 
Universal Form Clamp Co., copy- 


tight owners. Fig. 3a 


Pressure -100 |b. per sq.ft. 


A 
See yey div edah ae) 
Pressure - 100 |b.per sq. ft. 


Fig. 3b 


Key {HL 


Figs. 4a & b—The roughness of the wall texture at the right will permit 
greater deflection of the form sheathing than the smooth surface shown 
at the left. 


TABLE 1—Safe Working Stresses (psi) and 
Moduli of Elasticity of Various Kinds of Lumber 
for Form Construction { 


Com- 
Com- pres- 
pression] sion 


perpen-|parallel Modulus 
dicular to of — 
to grain rain elasticity 


Bids il 
t 


Douglas Fir, coast 
region—No. 1 
Praden ere ae SOO 

Hemlock, west 
coast—No.1 


1,600,000 


grade@annanceee 1800 1,400,000 
Larch—common 

structural grade.| 1800 1,500,000 
Pine, Norway— 

common struc- 

tural grade...... 1375 1,200,000 
Pine, outhern— 

No. 1 grade..... 1800 1,600,000 


Pine, Southern 
Longleaf—No. 1 
longleaf grade.. 

Redwood, Heart— 
structural grade.| 1625 

Spruce, Eastern— 
structural grade.| 1625 


1,600,000 
1,200,000 
1,200,000 


+The working stresses given in this table are approximately 25 
per cent greater than ordinarily used for permanent construction 
and for the grade and sizes (2-in. thickness or less) of lumber gen- 
erally used for forms, because forms are temporary thereby re- 
ducing the effect of time yield. Basic data for this table were taken 
trom National Design Specifications for Stress-Grade Lumber and Its Fastenings, 
1950 Revised Edition, Recommended by National Lumber Manu- 
facturers Association, Washington, D. C 


{L =length of member in inches; d=least dimension of the mem- 
ber in inches. 


tion. A small deflection that would not be noticeable in 
a texture produced with square-edged rough lumber is 
quite objectionable in a surface intended to be very 
smooth, particularly in one made with a form liner to 
eliminate joint lines. If the surface is near street level, or 
can be observed from a short distance, less deflection is 
permissible than in upper stories where slight irregulari- 
ties are not noticeable. Under any circumstances, the 
deflection of sheathing, studs and wales should not be 
greater than 1/270 of the span. As a rule, the size and 
spacing of studs and wales will be governed by the 
stresses in bending and horizontal shear, but the deflec- 
tion of sheathing is generally the determining factor. 


6 


Span of sheathing 
Q=\0" 


Figs) 


In the formulas given below for deflection, the modu- 
lus of elasticity of the material appears. The moduli of 
elasticity of the various kinds of lumber have been deter- 
mined by tests. It is evident from a study of these values 
(Table 1) and the formulas for deflection, that for the 
same loads and span some woods will deflect much more ~ 
than others. Due consideration should be given to this 
fact in the selection of lumber, particularly for sheathing. 

For a uniform load, as carried by the sheathing, and 
disregarding continuity because of the frequent necessity 
for using short lengths, the deflection will be 


3 eee! Swit 
D (deflection in inches) = 384x 12x El (1) 


in which 


uniform load plf* 

= span in inches, center to center of supports ) 
modulus of elasticity | 
moment of inertia (See Table 2—use the proper 
value, depending on whether the lumber is rough, | 
S2S, S2E or S4S). 


Problem 1—Determine the maximum deflection of 1x6 | 
Southern (No. 1 grade) pine sheathing S4S, if studs are 
spaced 16-in. centers, and concrete at 50 deg. F. is placed. 
at the rate of 2 ft. per hour (sheathing continuous over | 
several studs). (See Fig. 5.) Assume the form to be 10 ft. | 
deep. Because the form is deeper than the depth at which 
maximum pressure will be exerted at the prescribed plac-. 
ing rate, the entire form will be designed for the maximum 
pressure of 440 psf** (Fig. 3b). 


w = 440 X .47 = 207 plf 


w 
l 
EB 
yi 


1 = 16in. | 
E = 1,600,000 (Table 1) 
P= 92 (Table 2) 


z= 5 x 207 X 16+ ey: 

D = 37012 X 1,000,000 X 22 O42 
*plf—per lineal foot in pounds. | 
**psf—pounds per square foot. 


TABLE 2—Properties of American Standard Board, Plank, Dimension and Timber Sizes 
Commonly Used for Architectural Concrete Form Construction { 


5 M fi : : 
and American standard sizes Area of section ornens eee sects Oe feet 
rough in inches A=bh sq. in. f= pees per 
3 12 6 lineal 
inches S28 S2E S48 Wa 
boh beh boh Beh S28 S2E S48 piece 
4x1 4x25¢ 35%x1 3 54x25% 4.0 ; ae 
6x1 6x%_ | 55¢x1 554x%, || 6.0 ‘ar| ‘sal ‘e7) 3 
8x1 8x26 7 x1 7 6x6 8.0 : J x 81 1.25 .76 % 
10x1 10x59 Ral 94x @ 0.0 ; 7.42 40 79 38 WO il fete! 97 56 
12x1 12x%o | 11%x1 114%x%%@ 2.0 ae 8.98 48 .96 46 122392 Tle7, 1 
4x14 4x1% 3%x1\% 34x14 5:0 2 5 75 94 .68 5/y» 
6x14 xl 55x14 | Sxl, |} 7.5 : 1.13] 1.46] 1.06 % 
8x1\% xl, 7 %x1\% 7 Maxl, 0.0 A PS 1.95 1.41 56 
10x14 | 10x1ly% 9x1 9x1, PAS) i IWSSiie2. 47, 1.79 1!/24 
12x14 | 12x1% | 11%x1\ | 11%x1% 5.0 : 2-262 99) eee 14% 
4x1% 4x15% 3%x1\% 354x156 6.0 Bh 2s} |) ye) 76 aThe) 1.02 .68 1 as) 136i). O04 % 
6x1% 6x15% 5%x1l4% 5 5%x15% 9.0 7.88} 8.44] 7.38 Wale) 1.58 1.06 WZe|| Belli 1.62 34 
8x1% 8x1% 74%x1% 7 4x1% 2.0 | LOL50) 11-25) |\5 9784 it yal Zaei lal 174 2230 jee S i 2.15 1 
10x1\% | 10x15% 9%x1% 9M4x1% SONS 1 S425) 2847. 1.88 2167: 1.79 2.87) |\eeSoeD Oil a7 S 14% 
12x1% | 12x1% | 11%x1% | 11%x1% 8.0} 15.75] 17.25|15.09 2.26 St23 25197. 3:45) 4.31 || 53:30 1% 
4x2 4x1% 3 5%x2 3%x1% 8.0 6-50)) 7-251 5.89 1.43) 2.42 i730 1576) |e. 42 1.60 2 
6x2 6x1% 5 54x2 5 5x1 5% Z20 9.7 12 SaaS 25) Sle 7/3) 22011 2204) |on7 Sees 4S 1 
8x2 8x1 5% 7 x2 7%x1% 6.0 |} 13.00 | 15.00] 12.19 2.86 5.00 2.68 Sie || i{010)]) <i-sh0) 1% 
10x2 10x1% 94%x2 94x15 0.0 | 16.25] 19.00} 15.44 Siete! 6.33 3.40 4.40| 6.33} 4.18 1% 
12x2 12x15 | 11%x2 11%x1% 4.0 | 19.50] 23.00} 18.69 4.29 7.67 4.11 5.28| 7.67| 5.06 2 
2x4 | 156x4 | 2x35% 154x354 || 8.0] 6.50| 7.25] 5.89]| 8.67| 7.94| 6.45 4.33] 4.38| 3.56]  % 
2x6 15%x6 2x5% 154x5 5% 2.0 Siar Ae) | il sl edey| | Se)ai 29.25] 29.66] 24.10 OFS 101558257 1 : 
2x8 154x8 2x7 % 1%x7% 6.0 | 13.00} 15.00] 12.19 69.33 | 70.31) 57.13 17.33 | 18.75] 15.23 1% 
2x10 15x10} 2x9\% 1%x9% 0.0 | 16.25] 19.00 | 15.44 135.42 |142.90 }116.10 27.08 | 30.08 | 24.44 1% 
2x12 15x12} 2x11\% 154x114] 24.0 | 19.50 | 23.00 | 18.69 5 53.48 |205.95 39.00 | 44.08 | 35.82 2 
3x6 5 8.0 | 15.75 | 16.88 | 14.77 : 47.2 44.49! 38.93 L557 SS S82 ses 4) 1% 
25%x7% 4.0 | 21.00 | 22.50 | 19.69 ||128.00 }112.00 |105.47 | 92.29 28.00 | 28.13 | 24.61 2 
3x10 25x10} 3x9\% 254x9 4 0.0 | 26.25 | 28.50 | 24.94 |1250.00 |218.75 |214.34 |187.55 43.75 | 45.13 | 39.48 2% 
3x12 254x12| 3x11\% 254x114 36.0 | 31.50 | 34.50 | 30.19 ||432.00 |378.00 |380.22 1332.69 63.00 | 66.13 | 57.86 
NOTES: b=width of piece or dimension perpendicular to direction of load. 
h=depth of piece or dimension parallel to direction of load. 
_ 84S—all figures under this heading apply also to pieces S1S1Z, S1S2H and S2S1E. 
tBasic data for this table taken from Wood Structural Design Data, Vol. 1, by National Lumber Manufacturers’ Association. 
CAS : 16 = allow i i 
The permissible D is not more than —~ = .059; there- a " : able stress in extreme fiber in 
270 bending (Table 1) 
fore, the size boards for the span and load assumed is s rf dul at b bh? Table 2 
: ; : (i = section Modulus oO 1€ member — a 
satisfactory as far as deflection is concerned. It is seldom 6 ( € 2) 


necessary to determine the stress in sheathing due to 
bending and shear. The method of determining such 
stresses, which is discussed in the following paragraphs 
and illustrated by Problem 2, is also applicable to 
sheathing. 


Bending and Shear 


Sheathing and studs may be simply supported at two 
points, but much more commonly they are continuous 
Over several spans. If simply supported, the bending 
moment is 


M = 1.5wl” (2) 
and when continuous over more than two spans, 
M = 1.2wi” (approx.) (3) 


in which M = bending moment in in.-lb. * 


w = uniform load plf 

! = span in ft., c to c** of supports. 

The resisting moment of the member being designed is 
M, = fS (4) 
in which M; = resisting moment in in.-Ib. 


*in.-lb.—inch pounds. 
**c to c—center to center. 


Since the resisting moment must equal the bending 
moment, the allowable span is determined by equating 
M, = M and solving for /, thus: 


fS-=  1.5wP 
ryS9 
(pa 
1.5w (9) 
or 
fS = 1.2wP 
! 1.2w (6) 


Likewise, the maximum allowable load, depending on 
the degree of continuity, can be obtained as 


For short spans and heavy loads, the shear on the 
member at the supports (at the studs in the case of sheath- 
ing and at the wales in the case of studs) may determine 
the size of member required. It is sufficiently accurate for 
all conditions of continuity to compute the shear as 


y= > (7) 


in which V = shear in lb. 


” 
i 
0 
2 
Gq 
1e) 
O) 
£ 
Oo 
ra 
raw 
0p) 


i 


w = uniform load plf 

] = span in ft. c to c of supports. The unit shearing 
stress on the member, which must not exceed the allowable 
horizontal shear (Table 1), is 


1.5V 


in which v = unit shearing stress psi 

b = actual width of the member in inches 

h = actual depth of the member in inches 
By substituting the value of V (Eq. 7) in Equation 8, the 
allowable span is determined in terms of v, b and h. 


_ Avbh 


[BS ore (9) 
or allowable load per lin. ft. is 
w= aes (10) 


Problem 2—Determine the maximum allowable spac- 
ing of wales, if 2x4 Southern (No. 1 grade) pine studs 
S4S are spaced 16-in. centers and concrete at 50 deg. F. 
is placed at rate of 2 ft. per hour. Studs are continuous 
over several spans, and the form is assumed of such 
depth as to require it to be designed for the maximum 
concrete pressure. (Fig. 6). 


w = 440 X 1.33 = 585 plf (Fig. 3) 

f = 1800 psi (Table 1) 

S = 3.56 (Table 2— 
See footnote) 

y = 155 pst (Table 1) 

b = 1% in. 

h = 3% in (Table 2) 


To determine spacing of wales for bending, substitute in 
Formula 6 
_ [1800 X 3.56 
i 
NTS 585 


= 3.02 ft. 


for shear, substitute in Formula 9 
= AES(=155 Exel O20 a Oo 
3889 
Since the computed spacing exceeds that indicated as 
satisfactory by experience, the maximum allowable wale 
spacing of 24 in. shall be used. 


= 2.08 ft; 


Wales 


Wales differ from studs and sheathing in that they sup- 
port a group of concentrated loads, transmitted to the 
wales by the studs; so it is necessary to determine the 
bending moment and shear for a group of equal concen- 
trated loads rather than for a uniform load. 

The spans between ties should never exceed 36 in. and 
a maximum tie-spacing of 27 in. is preferable unless 
double 2x6-in. wales are used, for which a somewhat 
greater spacing is permissible. The spacing of ties and 
the dimensions of wales will be determined by the hori- 
zontal shear resistance of the wales or the stress in bend- 
ing. Deflection is seldom a factor in wale design. 

The maximum shear will be found when a stud is 
located immediately beside a tie, for which condition 

eps se “40 se a 
in which (11) 

] = distance between ties in in. 

P = each concentrated load in Ib. 


a = distance center to center of studs 
n = number of studs between ties. 


The unit shearing stress on the wales is found by 
Formula 8. 

With satisfactory accuracy, the maximum bending mo- 
ment may be considered to be under the center load of a 
group consisting of an odd number of equal concentrated 
loads when the center load is placed at the center of the 
span. Making allowance for continuity, the maximum 
moment will then be 


for 1 load m=" | 


4P 8 
for 3 loads M = = G41 — a) 


There will seldom be more than three studs between 
ties; so one of the above formulas will be applicable for 
practically every case. 

The resisting moment will be the same as given in 
Formula 4. 

Problem 3—Determine the maximum allowable spac- 
ing of ties for double 2x6 Southern (No. 1 grade) pine 
wales S4S spaced 24 in. apart with studs spaced 16-in. 
centers. Pressure of concrete is 440 psf. (Fig. 7.) 

The load carried to the wales by each stud will be 

= 440 X 1.33 * 2 = 1170 Ib. 

Assume the wales to have a clear span of 25 in. and 

there will be a maximum of two studs between ties; 


therefore only the first two terms of Formula 11 need 
be used to determine 


V = 1170 + TO 16) _ 1590 Ib. 
and by Formula 8 
: 1.5 X 1590 130 psi 


B21 625551625 | 
This is within the allowable horizontal shear (155 psi 
for Southern pine); so the tie-spacing assumed is satis- 
factory if the wales are not over-stressed in bending. 
Check for bending stress by substituting in Formula 12 
for a single load midway between ties, thus: 


pa a 5850 in.-Lb. 
and by Formula 4 
5850 
f= 3303.56 = 822 psi 


This stress is less than the allowable in the extreme 
fiber; so the assumed tie-spacing is satisfactory. 


Ties 


The spacing of ties having been determined on the 
basis of the strength of the wales, the capacity of the ties 
must be checked against the allowable values given in the 
manufacturer’s catalogue, or the required size of the ties 
must be computed. A satisfactory tie for architectural 
concrete work, which will be more fully discussed later, 
is the ordinary pencil rod. The size rod required is easily 
computed by the formula 


A, = 


P 
. . fs 
in which 
A, = cross-sectional area of pencil rod 


MILL FOR MAKING FORMS 


HE cost of forms is an important part of the cost of an 
eas concrete job, and the mill’s efficiency in 
making forms materially affects their cost. The larger the 
job, and therefore the greater the amount of equipment 
necessary in the mill, the more influence the mill layout 
will have on the cost. Obviously, for a small job, the mill 
consisting of little more than a saw and a bench will 
have little effect on the final cost, but a large mill should 
be planned carefully. 

Definite rules for the location, size and equipment of a 
orm mill cannot be given; because they are dependent 
ipon the conditions of each individual job. However, 
-Onsideration of a few of the general requirements which 


16" 16" 
Pere ss itt a ee 
S| Eo 
——S aa 


P = pressure of concrete times the contributing area, 
namely the distance between wales multiplied 
by the distance between ties 

We allowable working stress for steel (25,000 psi for 
the temporary loads encountered in form 
construction). 


If the capacity of the selected size tie is exceeded by the 
strength of the wales for a given spacing of ties, then the 
spacing must be reduced or the size of tierods increased, 
whichever may be most economical, depending upon the 
contractor’s equipment. Large ties are more difficult to 
remove from the concrete, which fact should be taken 
into consideration. Most frequently used are Y4-in. and 
¥-in. round rods; Y%-in. and 5-in. rods may occasion- 
ally be required. It is better, however, to reduce the spac- 
ing of the ties or wales to avoid using the larger sizes. 


SECTION 3 


apply to practically every large job will aid in the design 
of the plant for a specific project. 

The mill should be located as close to the building as 
possible, but space should be allowed for storage of fin- 
ished forms. It is also advisable to place the material hoist 
and concrete plant in the most central position and im- 
mediately adjacent to the building. This is important 
because of the labor required for transporting the con- 
crete into the building, if the plant is too far removed, 
as compared with the work involved in handling forms. 
The space available and the location of the building site 
in relation to the street or streets will influence the mill 
layout. If at all possible, the mill should be located so 


9 


that the operation is progressive from the point where 
lumber is received to the place where finished forms are 
delivered to the erection crew. Similar considerations 
affect the interior layout of the mill. 

A storage space for incoming lumber will be necessary. 
The space required will depend on the size of the job and 
whether materials can be obtained on short notice in 
small lots or must be stored in carload or larger lots. The 
receiving yard should be convenient to the saws to mini- 
mize handling of material. It should also be convenient 
to the bench carpenter’s fabricating panels, because much 
of the material will not have to go through the mill. 
Material as it is received should be piled according to 
sizes, so that no time will be lost in finding a desired size. 
On especially large jobs where there are manystockpiles, 
some contractors have found it advisable to label each 
pile in the yard and prepare the piles for the bench car- 
penters with signs showing the sizes. This enables the 
stockman to make quick selection of material and avoids 
waste of cutting pieces uneconomically. 

Next to the mill and as close as possible to the material 
hoist, space should be provided for storage of completed 
panels or partially assembled forms ready for erection. 
This space should be convenient to the benches within 

he mill or just outside the mill where the panels are 
built. 

A well-equipped mill for an average job will require a 
cut-off saw and ripsaw, or one that will perform both 
operations. Usually, a swing type cut-off saw is best 
where separate saws are used. The saws should be capable 
of handling at least 2-in. material. They should be adjust- 
able to cut or rip at any angle or bevel because of the odd 
shapes that may be required. If there is to be considerable 
ornament, a band saw will reduce the amount of hand- 
work. A portable electric saw will save the bench car- 
penters’ time in fabricating panels. Adjustable benches 
made by laying planks on sawhorses are better than per- 
manent benches, because of difficulty in working around 
panels of varying sizes when the bench is made large 
enough to accommodate the largest panels. 

A stock rack for rippings and moldings reduces break- 


ERECTION ACCESSORIES 


Ghee care exercised in the selection and proper use of 
erection accessories is reflected in the quality and 
cost of the work. There are many patented devices on the 
market having merit for some classes of work, but all 
should be studied carefully before being used on an archi- 
tectural concrete job, because of the possible effect on 
appearance. 


10 


age and keeps various sizes and shapes of pieces sepa- 
rated. With such a rack, consisting of 15 to 20 compart- 
ments 12x15 in. in cross-section and 10 to 12 ft.in length, 
the mill man can tell when certain sizes run short and 
will avoid delay for the bench carpenters. 

If the job is large enough, a planer and boring machine 
are economical. Emery wheels and other tool sharpen- 
ing equipment are always desirable. 

The mill should have a roof to protect the equipment 
and men, but the sides should be as open as possible for 
easy material handling. Cramped space should be avoided 
but unnecessary room is likewise undesirable. A clear 
space of 4 or 5 ft. around the saws with their haul-off 
and feed tables is about right. There should also be 3- or 
4-ft. aisles between benches, so carpenters do not inter- 
fere with each other. 

The assembly benches are frequently just outside the 
mill. Such an arrangement has the advantage of requir- 
ing much less space in the mill, and usually allows more 
room around the benches. A disadvantage is that in- 
clement weather interferes with the work on benches, 
whereas, if under cover, work could proceed on panels in 
preparation for the erection crew when outside work is 
resumed. If this is done, a few extra men in the erection 
crew can often make up for lost time. 

Where a building occupies the entire site and there is 
no vacant land adjoining as in a downtown area, the mill 
must often be strung out along the building site on the 
sidewalk. This may complicate the layout slightly, but 
observance of the general requirements will result in an 
efficient arrangement. 

A space 10 to 12 ft. wide is required, of sufficient length 
to accommodate the equipment. The mill must be placed 
next to the street, to allow delivery of materials without 
interfering with pedestrians. Pedestrians are provided 
with a walkway, covered for protection, between the mill 
and the building. A light fence along the street side is 
necessary to protect the workmen from passing vehicles. 

If the building is one of several stories, it is often desir- 
able to place the mill inside the building, particularly if 
working and storage space outside is limited. 


SECTION 4 


Nails 


Nails are an essential, but their improper use adds 
appreciably to the cost and may even result in damage to 
the concrete. Forms must be substantial and their com- 
ponent parts securely held together, but the use of too 
large or too many nails should be avoided. Labor re- 


Fig. 8—In a rough texture the 
impression of the heads of 
common nails is not objec- 
tionable but would mar a 
smoother surface. 


| le SEINE aa i sts git gate ne 


quired for fabrication, erection and stripping will be 
saved thereby and much greater reuse of the lumber can 
be made, as it will not split and break so frequently when 
stripping. 

Box nails are best for attaching sheathing to studs for 
built-in-place forms, because the shank is thinner than 
that of common nails and will pull loose more readily. 
The size will depend upon the thickness of sheathing. 
For nominal 1-in. sheathing or %-in. and thicker ply- 
wood, 6d nails are recommended. Common nails of this 
size are better for panel forms because such forms must 
stand considerable racking and abuse. 

Fiber board and thin plywood form liners over sheath- 
ing should be attached with small nails having thin flat 
heads. Three-penny blue shingle nails are generally con- 
sidered best for this purpose. The heads of these nails 
leave but a very faint impression in the concrete, while 
the small-diameter shank pulls out of the sheathing easily 
without pulling the head through the lining material, 
which would make the lining unsatisfactory for further 
use unless the edges were trimmed. 

Common nails should be used sparingly, except in the 
fabrication of forms to be reused several times without 
alteration. Their holding power makes them difficult to 
remove and their heads make a more noticeable impres- 
sion in the concrete than do box nails. For nailin g kickers, 
blocks, braces, reinforcing for wales, and similar pieces 
that require nails of considerable holding power and yet 
must be removed readily, use double-headed nails. 

Double-headed nails can be pulled easily and quickly 
with a claw hammer or stripping bar without bruising or 
otherwise damaging the lumber. The size will depend 
upon the material to be nailed and the load to be carried. 


Bolts 


Bolts, except as ties, are not so frequently used in the 
erection of building forms as in forms for heavier con- 
struction. A bolt made of a rod threaded at both ends and 
provided with nuts is sometimes preferred to a standard 


Fig. 9—Double-headed nails were used in assembling this form so that 
the nails could be pulled easily and the form stripped without damaging 
the sharp edges of the reveal. 


bolt. When a bolt of this kind is used as an anchor at a 
construction joint to hold the form above tightly against 
the hardened concrete, the shank of the bolt can be un- 
screwed, thereby losing only the nut, and leaving no 
metal near the surface to corrode. For easy removal, the 
thread on the end of the rod in the concrete should be 
only long enough to receive the nut. For this purpose 
¥g-in. bolts are generally used. Further information re- 
garding construction joints is given on pages 47 and 48. 


Ties 


There are a number of factors to consider in the choice 
of form ties. First cost is important but should never be 
a controlling factor. Possible reuse; speed and ease with 
which the ties can be placed and removed; adaptability 
to built-in-place and panel forms; positiveness of action; 
and most important of all, the effect on the appearance 
of the finished job, should be carefully considered. They 
should not permit leakage of mortar or water at the form 
surface. 

Because the first cost was little, wire was at one time 
the most common form tie. It was passed through the 
forms and twisted about the studs, or otherwise drawn 
taut. But at best, such wire ties were never satisfactory 
because the wire would stretch and bite into the wood 
under pressure of the concrete, causing irregularities in 
alignment and wall thickness. 

There are ties available with which wire is used that 
are satisfactory, but to be used for architectural concrete 
work the wire must be annealed and machine straight- 
ened and formed. A plate must be used under the loop 
of the wire against the studs or wales to prevent cutting 
into the wood and a positive cinching device must be 
used to grip, stretch and tie the wire without twisting it 
between the forms or otherwise making it impossible to 
pull the wire from the hardened concrete. 

The most satisfactory tie is one that is adjustable in 
length and leaves no metal closer than 14 in. of the sur- 
face. Ties that can be completely removed from the wall 


Vhs 


or that break back the prescribed distance are acceptable. 
Because perfection of finish is the ultimate aim in archi- 
tectural concrete, ties fitted with lugs, cones, washers and 
similar devices to act as spreaders are not suitable since 
they leave blemishes on the surface. As a rule when a tie 
is pulled or broken off it should not leave a hole larger 
than % in. in diameter and a tie leaving an even smaller 
hole is preferred. Simplicity is always a desirable attribute 
in form ties. The less elaborate a tie and the fewer 
“gadgets” there are to handle, the quicker it can be in- 
stalled—which may mean an appreciable saving on the 
job. 

Several ties are shown in Fig. 10 which meet the re- 
quirements for architectural concrete work. The sketches 
are intended to illustrate types of ties and not the prod- 
uct of any manufacturer or manufacturers. It is quite 
possible there are other ties on the market equally accept- 
able or that will be developed to meet the basic require- 
ments for architectural concrete construction. 

Fig. 10(a) shows a tie consisting of a straight un- 
threaded pencil rod with “‘buttons” or clamps which are 
slipped over the rod and bear against the wales. The 
clamps grip the rod by means of a set screw which puts 
a crimp in the rod to prevent the form from spreading. A 
wood spreader must be used. The rods are entirely with- 
drawn from the wall when the forms are stripped. 

The tie shown in Fig. 10(b) consists essentially of two 
lag screws which are removed from the wall when the 
forms are stripped, and a part that remains in the wall 
into which the lag screws are threaded. This inner part 
must be short enough so that no metal will remain closer 
than 114 in. of the outside wall surface when the lag 
screws are removed. A wood spreader must be used with 
this tie because cone spreaders on the lag screws are not 
acceptable. 

Fig. 10(c) illustrates the “‘snap-in’’ type of tie which is 
satisfactory for architectural concrete providing every tie 
breaks back the required distance from the surface of the 
wall. Snap-in ties are usually provided with knobs or 
other devices on the ends of the rod which are engaged 
by clamps or holders and some device such as the small 
lugs near the middle of the rod to prevent turning in the 
concrete when the rod is twisted or snapped off. These 
details generally require the drilling of a hole through the 
sheathing appreciably larger than the rod to permit the 
rod to pass through. The metal discs sometimes used as 
spacers with snap-in ties cover the holes in the sheathing 
and prevent leakage, but such discs are not acceptable on 
an architectural concrete job. It is necessary to plug the 
hole in the sheathing in some other way or provide rods 
with a removable end so that the hole in the outside 
sheathing need be only slightly larger than the rod. The 
clamps or holders at the ends of the ties must be secured 
positively against loosening or movement when concrete 
is placed or forms are vibrated. 


12 


Rod to be 
withdrawn 
from wall 


(a) 


No metal to 


remain closer 
than |4" of 
surface 
(b) 
/ Hole to be as small as 
i) possible to receive tie. 
I Plug hole if necessary 
to prevent leakage 
Cc) t , 
( Vee 
- k\ Tie must brea 
backat least IN 
b from surface V 
A srencer plate Z 
ae Sy UA A 
Special care must 
be taken to insure 
removal of all 
wood spreaders 
a NZ 
y, Rod to be 
withdrawn 
from wall 
End rods to be 
as withdrawn 
(e) i a Sa 


Nail to stud 
to act as 
spreader 


Fig. 10 


Fig. 10(d) shows a tie consisting of a standard SAE 
threaded rod provided with a nut and plate at each end. 
A wood spreader must be used with this tie. The rod is 
entirely withdrawn from the wall when forms are stripped. 

Fig. 10(e) illustrates another tie in which all metal is 
removed from the wall. A hole through each outside rod 
permits driving a nail into the studs on each side of the 
form to act as a spreader and the shoulder bearing against 
the sheathing fixes the thickness of the wall. When forms 
are stripped one outside rod is disconnected and the other 
outside rod, nut washer and inside rod are withdrawn 
toward the back of the wall with a rod puller. 


Spreaders 


Spreaders must be provided in wall forms to prevent | 


the sides being forced in when the tierod clamps are 


/ 


{Wire for 
pulling up 
spreaders 


Spreader 


Hole for wire 
off center 


Form 


tightened. There are as many types of spreaders as there 
are clamps or ties and each has its merits for certain uses. 
The objection that applies to many ties for architectural 
concrete work also applies to most spreaders, namely, 
they leave too large a hole at the surface to be plugged. 
It is difficult at best to match the color and texture of the 
wall with the mortar used for plugs. Therefore, the hole 
to be plugged should always be as small as possible. A 
good solution of the problem if internal spreaders are 
required is the old-fashioned wooden spreader made of 
rippings of 1-in. boards. When the spreaders are removed 


PLANNING THE JOB 


ORMWORK is too frequently left to the carpenter fore- 

man on the job to lay out and detail. Such practice is 
not desirable, since there is no time in which to plan and 
study the job after construction has started. The quality 
of the finished job and the contractor’s profit or loss are 
dependent to a great degree upon the attention given to 
the planning of forms in the office and drafting room be- 
fore a board is sawed or a nail driven. 


Important Considerations 


Each job must be studied at the time it is being esti- 
mated and when forms are being designed. No two jobs 
will be formed exactly alike. There are, however, certain 
important considerations applicable to all jobs and a 
thorough analysis of each should be made. They are: 


Fig. 12—A well-constructed form is illustrated. Note the heavy vertical wales in addition to the 
horizontal wales, Such bracing maintains true alignment of the form. 


from the forms, the only holes to be plugged are those 
left by the ties. To be sure that none are buried, all 
spreaders except the top row should be removed before 
closing clean-out holes. The top row is removed when 
the concrete reaches that level. 

A convenient way to be certain that all spreaders are 
removed from the wall is shown in Fig. 11. A wire fas- 
tened securely to the bottom spreader passes through a 
hole in each of the spreaders above. As concrete is placed 
a pull on the wire will dislodge the lowermost spreader 
until all are removed. 


SECTION 5 


. Contemplated progress or speed of erection. 

. Length of time forms must remain in place (speci- 

fied by architect or based on good practice). 

. Number of reuses of material. 

4. Type of forms to be used—panels, built-in-place, or 
a combination of the two. 

5. If panels are to be used, shall they be detailed for 
reuse without alteration or shall they be cut down, 
added to and otherwise altered to fit varying condi- 
tions as the job progresses? 

6. Location of construction joints and control joints. 

. Order of erection. 

8. Must all erection be done by hand or will power 
equipment be used? 

9. Order of stripping. 


No — 


Ww 


~ 


13 


Fig. 13 


It is obvious that the person or persons who decide on 
the above questions must have the entire job in mind, 
since the interrelationship of all the operations will have 
a bearing on how the formwork is to be planned. 


Speed of Erection 


The time for completion of the entire job may be speci- 
fied, or the contractor may be required to state in his 
proposal the number of days necessary. Out of the total 
time necessary to complete a building, it must be deter- 
mined how much time will be required for the concrete 
work. The interior structural concrete, which is placed 
at the same time as the exterior architectural concrete, 
must be considered. In regard to the latter, the simplicity 
or elaborateness of detail makes considerable difference. 

The progress of a job will depend to a considerable 
extent on whether it is properly manned. A carpenter 
gang of 14 to 18 carpenters, and 6 to 9 helpers should be 
provided for every 10,000 sq.ft. of contact area of forms 
required for a single floor. This crew should complete 
one floor in about five or six working days of eight hours 
each. For larger jobs, an increase in the form area factor 
can be made because of repetition of forms and the 
greater efficiency of the crew toward the end of a large 
job. A gang of the size mentioned may fabricate, erect 
and strip 10,000 sq.ft. of panel forms in 40 to 48 working 
hours, taking into consideration all types of forms used 
on a job. If all forms must be erected in place, the same 
crew will require 10 to 20 per cent more working hours 
to construct and strip the same area of forms. 

In exterior walls, if the ornamentation requires large 
areas of milled forms or waste molds, allowance must be 
made for additional time for erection and stripping. The 
exact amount depends upon the complexity of the detail 
and must be learned by experience. A study of a few 
typical examples will help as a guide to the estimator’s 
judgment. 


14. 


A facade involving simple detail such as that illustrated 
in Fig. 13 requires only slightly more labor for forming 
than would be necessary if the fluted pilasters and the 
ornamental spandrels were plain. Since the fluting is flush 
with the wall surface, it is not necessary to cut the sheath- 
ing and no offsets need be formed. The fluting is formed 
by simply applying corrugated iron to the face of the 
straight wall forms as shown in Fig. 14. An allowance of 
15 to 30 per cent additional time over that required if the 
walls were unornamented should be ample for construct- 
ing the outside forms for the entire area involving the 
ornament. 


gated black iron ie 


; 7: oar, » At woe ai ee 
Banene We Sey ee Gg. — Corru 
Oe: Mt ay) EO ~ °. Se i OF es ae “iS Ceres ts 


Fig. 14 


If ornamentation is somewhat more elaborate, as that 
shown in Fig. 15, the forming time will be considerably 
increased. Application of V-strips in the piers, setting of 
waste molds for spandrels, and forms for the fluted mul- 
lions will increase forming time from 75 to 100 per cent 
for the outside forms. The inside forms will require the 
average time to construct. 

Still more elaborate detail, particularly projecting cor- 
nices, water tables and ornament requiring intricate 
waste molds, may increase labor for erection and strip- 
ping still more for those areas. An extreme case may re- 
quire two to three times the normal time for forming, but 
such jobs are unusual. 

It is poor economy to force a carpenter gang to build 
more forms in a day than should normally be expected 
of them. Careless work will result which may cost more 
in the end. 

Placing of reinforcement can usually be carried on 
simultaneously with erection of forms, so that operation 
need not materially affect the time required for comple- 
tion, assuming that the job is properly organized and an 
adequate crew of steel-setters is used. 

On the ordinary job the work should be planned so 
that the maximum yardage of concrete to be placed in a 


day does not exceed the capacity of the mixer at the rate 
of one batch every two minutes. This rate allows for a 
mixing time of one minute and for unavoidable delays. 
If the job is large enough to warrant more than one mixer, 
the placing rate will be in proportion to the number and 
size of mixers. Using a 4-yd. mixer, a day’s run will be 
between 100 and 120 cu.yd. of concrete. To handle this 
yardage of concrete, a crew consisting of 20 to 25 
laborers will be required. 

Perfection of surface and quality of the exposed con- 
crete must be the constant objective. Small mixers even 
under 4-yd. capacity are frequently used to advantage 
because the concrete is not delivered to the forms in too 
large quantities. Ample time must be allowed for spad- 
ing, for a thorough job cannot be done if a large batch of 
concrete is dumped into the forms at one time. 

Some account should be taken of additional time re- 
quired for placing concrete in forms involving quite large 
areas of waste molds. If there are undercuts, it may 
be necessary to work the concrete into the mold by hand. 
More care is needed when spading around waste molds, 
to insure filling in the detail and avoid damaging the 
mold. If there is a considerable area of waste molds, 25 to 
50 per cent more time may be required for placing the 
concrete against these molds than against ordinary forms. 

The time required for the various operations can be 
estimated within reasonable limits by applying the factors 
given above. In addition is the time that must elapse be- 
tween placing of concrete and stripping of forms. Allow- 
ance for shut-downs between different operations can 
largely be eliminated by dividing the job into two or 
three parts so that the work can be scheduled progress- 
ively. 


Time Forms Must Remain in Place 


Forms must be left in place long enough for the con- 
crete to gain sufficient strength to support its own weight 
plus that of any construction loads. Forms serve another 
important purpose, namely, protection of the concrete 
against early drying. Although curing of concrete can be 
accomplished satisfactorily by other methods, it is often 
neglected, particularly on vertical surfaces. Leaving forms 
in place a reasonable time is generally the simplest and 
best method to secure at least some degree of curing. 

Regardless of the adequacy of the concrete to support 
its own weight, no forms should be removed from either 
exterior walls or interior frame and floors in less than four 
days, unless other means are provided for continuous 
moist-curing or high-early-strength concrete is used. The 
time during which forms must remain in place need not 
delay the progress of the work if sufficient forms are avail- 
able. Whether it is more economical to delay the job, 
awaiting removal of forms, or to provide additional forms 
depends upon the overhead that goes on during delay 


Pd 


Fig. 15 


and any penalties that may be invoked for over-running 
the specified time of completion, as compared to the cost 
of extra material. 


Reuse of Forms 


To maintain a progress schedule without delays, it is 
usually necessary to provide sufficient wall forms for one 
complete story and for one-quarter to one-half of the 
next story, depending upon the size of the job. If this is 
not done, at least part of the carpenter gang must be idle 
until forms can be stripped. If the job covers a very large 
area so the concrete required between successive con- 
struction joints exceeds that which can be conveniently 
placed in a day, the job may be divided into two or more 
parts. Under such conditions, enough wall forms for one 
entire part and a portion or all of the second part should 
be provided. 

Because both the inside and outside of the building 
must progress together, at least one set of column forms, 
one set of slab panels and beam sides, two sets of beam 
and girder bottoms and two or three sets of shores will 
be required. 


Type of Forms 


Whether panel forms, built-in-place forms or a com- 
bination of the two should be used will depend largely 
upon the architectural treatment. Where they are suit- 
able, panel forms have many advantages. A saving in 
labor and material is made by doing as much of the work 
as possible on the bench and in the mill rather than from 
a scaffold. The use of power equipment in the mill and 
the fact that workmen have their feet on the ground 


15 


Panel forms are employed to greatest advantage where 
they can be used several times simply by raising them 
directly above their original positions or moving them 
laterally. Fig. 16 shows a good example of an elevation 
that lends itself to panel forms. It is a 13-story apartment 
building of uniform floor heights and uniform window 
openings from floor to floor. The panels used on this proj- 
ect extended from the construction joint at the sill line of 
one floor to the construction joint at the sill line of the 
floor above. A layout of the panels is shown in Fig. 17. 
Concrete was placed in two lifts, one from sill line to 
window head and the other in the spandrel from window 
head to the sill line above. Construction joints were car- 
ried all the way around the building and rustication strips 
were provided to conceal the joints. After concrete in the 
spandrel hardened, the panels were raised to the next story. 
Scaffolding was built right into the panel forms as shown 
in the details in Fig. 18. This scaffolding aided greatly in 
setting the panels and in tightening and removing the ties. 


te 
ec 


a 
Fig. 16—On the Parklabrea Towers Apartments in Los Angeles, one | B 
set of panel forms was constructed for each building. The form was r s 
raised from floor to floor as construction proceeded. Leonard Schultze r th 
& Associates, architects; Gordon B. Kaufmann and J. E. Stanton, 2 
associate architects; Starrett Bros. & Eken, Inc., contractors. a g 
B 
5 
a 
result in greater efficiency. Progress of the work is facili- | Ey eee ae 
tated because the panels can be made up in advance of eee eeices 
the time needed. By careful planning and detailing, con- er eet over = Ae 
siderable more reuse of material can be obtained in panels ee ick 
than in built-in-place forms. The size of panel will not brn Wap 
only depend on the architectural design but also on the - eee ieee! 
method of handling. If power equipment is to be used, §=>}-—_}=—==—— = 


panels may be made in very large sizes. If such equip- 
ment is not to be available, the panels generally should 
be small enough for two men to handle. 

Spandrel and pilaster forms can usually be made in 
panels, unless the detail requires waste molds or there 
are many angles and sharp corners in the ornamentation. 
Under such conditions, there would be danger of break- 


ing corners when stripping if the form were removed as 5 er 
; é =a 


a unit. The quality of the finished job must always dictate tg i de 
the construction methods used. Never use a panel form: a 
where “‘piecemeal” stripping is required to insure per- ee ee ee 
fection of detail, unless the panel is so constructed that 

it can be dismantled in pieces. Fig, 17 


ae 329) 5530 |3-9)/ 553) 13-9) 9-3a13- 99-3) piesa 3 


on 


16 


poill line 


} 


os 


319" 


12+0° 


Ss 


/A\ 
YA ea 


ales 


Floor line 


Window head 


FEL EP: PI 


t 
yw 
ic 
Vv 
(= 
‘ele 
Ui he 
i E= 
= \ @ 
w 
ht 
| 
2e|| / 
sil i a I. 
“|| we 
| oni 
) as 
| |] “wo 
4 = C 
| rat 
L_J-+— 


\ 
/ 


Vaal 


Fig. 18 


Sill line 


Fig. 19—Close-up of form shown in Fig. 16. Scaffolding was built into the panel 


forms. Form panels extended from window-sill line of one story to sill line of story 


above. Concrete was placed in two lifts for each story and the panels were then 
raised as a unit with gin poles resting on the floor construction. 


The forms in position for a complete story are shown in 
Fig. 19. 

Fig. 20 illustrates a typical job requiring that most of the 
forms be built in place. The spandrels are ornamented 
with considerable fine detail requiring either milled wood 
forms or plaster waste molds. The forms for the pilasters 
at the corners of the building and at each side of the 
entrance might be built as panels if special care is exercised 
in stripping. The fluted mullion forms, which must be lined 
with corrugated iron, may be built in place or constructed 
as panels, depending somewhat on the detail of the win- 
dow jambs. Since the parapet is to have a smooth surface, 
as indicated by specification of lined forms, joints between 
panels would be objectionable, and no matter how much 
care is taken, the joints between panels are more notice- 


= 


Control joint Tempered fiberboard lined forms 
Corrugated black 
iron lined form 


Te NIN 


= il : 


FA I 
i TT 
WH 


Construction join 


+ 
Tm 


i 


i) 


| | 
ae | 


Zplaster or wood | 
mold forms 


17 


ay 4 
: Control | 


Le | ; 

© join Q | 
Co) 

rG) 1 | 

‘| | 

i} 

+f te 

‘o} ; 

|} h Construction joint 
HH he tlt paaelabe er 
: X11 | 

© | | | | 

© | ee a 

HHL A ee ip | 

aN Ps 

m Same Construction joints] || 
tf} mesic tor otat 
iol | 1]/\f J] 

o| | 

| 

io ‘2 

SE Construction joi 

= | I 

© 

| 


{I 
\y HT 


HHI 
tJ} |i 
Wn 1) 


Fig. 21 


able than when the lining is carefully fitted in place. The 
backing can be made up in panels if the lining is applied 
after the panels are set. 

Fig. 21 shows a facade that is best formed with a combi- 
nation of panels and built-in-place forms. The detail up 
to the second-story window sills makes panel forms unde- 
sirable. For this part it would be best to erect the forms 
complete with sheathing as for a plain wall surface and 
then apply the necessary milled strips and pieces to form 
the detail. From this line to the head of the top-story 
windows, panels are ideal. Plywood panel forms would be 
especially well suited because each panel could be made 
from a single sheet. More than one piece should never be 
used where one will do, unless some pattern of joint lines 
is desired. If a board-marked surface is specified, the panel 
forms could be used, except for the parapet forms, which 
should be built in place in order to stagger the vertical 
joints in the sheathing. Panel forms made with ordinary 
lumber are unsatisfactory if two panels must join on a 
flat surface. 


Alteration of Panels 


Greatest economy in panel forms is obtained when they 
can be used repeatedly without alteration. On some jobs 
the panels may be reused by making only slight alterations. 
For the job illustrated in Fig. 21, the panels used to form 


18 


the pilasters can be used without alteration in three story 
heights and then changed slightly when used at the top of 
the pilasters. For the job illustrated in Fig. 16, three addi- 
tional rustication lines were specified between windows of 
the first story. Strips to form these lines were tacked onto 
the panels and remained in the concrete when the forms 
were removed. It was a simple matter to fill the nail holes 
in the panels when they were lifted to the next story. 

The extent to which panels can be altered economically 
will, of course, depend on the cost of new forms as com- 
pared to the cost of the alterations. 


Joints 


Two distinct types of joints are necessary in nearly all 
architectural concrete building walls. These are horizontal 
construction joints, often referred to as cold joints, where 
concreting is stopped and is allowed to harden before pro- 
ceeding with the next lift, and vertical control joints for 
the purpose of avoiding haphazard cracking. Because of 
their great influence on correct detailing of the job, the 
progress schedule and the appearance of the finished 
building, the location of these joints must not be left to 
chance. The architect designates the location of control 
joints on his drawings and usually shows where construc- 
tion joints are to be placed. If the location of the construc- 
tion joints is left to the contractor he should definitely 
decide where they are to be placed and should receive 
approval of the architect. The chosen locations must 
satisfy all architectural and structural requirements. 

Construction joints must be close enough together so 
that the quantity of concrete required between them will 
not overtax the capacity of the plant and crew to place it 
in a normal working day. When it is necessary to work 
several hours overtime, perhaps after dark, workmen are 
tired and there is an inclination to hurry. This generally 
results in careless workmanship and poor appearance. 

When panel forms are used, the construction joints 
should be spaced so that the panels will reach from one 
joint to the next. Intermediate joints thus will be avoided 
and better appearance will be obtained. 

Construction joints should be placed where they will be 
inconspicuous by taking advantage of architectural de- 
tails to obscure them. By placing these joints at sills and 
heads of windows they are broken into short lengths on 
natural lines in the architectural treatment, which makes 
them inconspicuous. They may be further concealed by 
rustication strips as was done on the job shown in Fig. 16. 
On the job shown in Fig. 22 the rustication strips were 
carried across large expanses of plain wall, making them 
an architectural feature. 

It is nearly always essential that a construction joint be 
provided at window heads. An exception is possible in 
some buildings of the column and spandrel type where the 
quantity of concrete in the columns is not large. Even in 


Fig. 22—Construction joints and control joints were carefully placed on this project to fit into the architectural design as indicated in Fig. 23. 
Portland Cement Association Laboratories, Skokie, Ill., Carr & Wright, architects; Turner Construction Co., contractor. 


these cases the concrete should not be placed in one con- 
tinuous operation from the sill line of one story to the sill 
line of the story above without interruption. The placing 
of concrete should be stopped at the window head and 
allowed to stand for at least an hour and preferably longer, 
depending upon weather conditions, to allow as much 
settlement and shrinkage as possible to take place before 
the spandrel and floor concrete is placed. 

The exact locations of the vertical control joints* 


*For more complete information see Control Joints available free 
from Portland Cement Association in United States and Canada. 


should be shown on the architect’s drawings and details of 
their design should be shown also. Care is required in 
building and placing the forms to see that the strips form- 
ing the joints are held rigidly in true, straight, vertical 
lines at their proper position. 

A detail of the control joint used in the building 
illustrated in Fig. 22 is shown in Fig. 24. 


Order of Erection 


The order of erection of forms has a direct bearing on 
the detailing and scheduling of all operations from order- 


Seneeen Vessel He 


aoe 
ee a a a 
"lI ba ea a 
Same RaaI Rustications 
at construction 


SIRS 


aaa 
SS SS 
ma ely 


Fig. 23 


19 


F rRoof line 


Yn 
= = ae ca © ace 4 
ale : 
£\§ e 
=|S = a Bars 
Tam oes AMA 
heb 9 “ ; Ve oa 2 
+ Cea aay we 
= & 
‘s poe floor ve ye 
ce iS 
s a ConTROL Joint 
c Bt = 
i) 
= £ 
a & 
z|2 
i 
ele 
= ° 
aa — 


Panel heigh 


PANEL SECTION 


anes Floor 


| -Tet'Studs Ieroen | 


Control joint at 
Wats of panel | 


] -— 2x 6" Wales -240"o.c. 


Cross SECTION AT END oF PANEL 


;-Basement 
floor 


——————? 


TYPICAL WALL SECTION 


Fig. 24 


ing of material to its passage through the mill and finally 
to its use. The erection schedule depends largely upon the 
type of building. There are three general plans of opera- 
tions ordinarily followed in architectural concrete work. 


Plan 1 


For one- and two-story buildings and the lower 
stories of tall buildings which are usually more highly 
ornamented than the stories above, the following proce- 
dure is recommended: 

1. Erect outside wall forms and bring them to line. 

2. Erect inside wall forms and floor forms. 

3. Check alignment, tighten braces and bolts. 


Plan 2 


Buildings consisting principally of columns and span- 
drels are generally constructed with panel forms which can 
be handled most conveniently from a deck, and so it is 
customary to: 


20 


1. Erect inside wall forms and floor forms. 

2. Erect outside wall forms. 

3. Bring forms to proper alignment, brace and bolt 
securely. 


Plan 3 


In tall buildings that have considerable ornamentation 
which necessitates the use of waste molds, milled wood and 
other special forms, the following procedure is best: 

1. Erect floor forms. 

2. Erect outside wall forms and bring practically to 

final line. 

3. Erect inside wall forms. 

4. Bring forms to final alignment, brace and bolt 

securely. 

If this order of erection is followed, the outside forms 
can be touched up and joints in wood or plaster molds 
filled, if required, before the inside forms are set. The waste 
molds and panels for the outside can also be handled most 
conveniently by using the floor forms as a working platform. 


Erection Methods 


Built-in-place forms are from their very nature erected 
entirely by hand, piece by piece. The only aid that can be 
offered by mechanical equipment is in hoisting lumber to 
the carpenters. In.a panel-form job, planning the job and 
detailing forms will be considerably affected by use of 
mechanical equipment for erection. 

Where hand methods only are used, it is generally ad- 
visable to limit the size of panel to one that can be handled 
by two men but if larger panels are necessary, it is desirable 
to use a hoist. A convenient rig for hoisting large panels is 
an ‘“‘A’”’-frame derrick equipped with a ratchet windlass. 
The derrick is set up on the floor forms above or on the 
floor just finished, and tilted over the wall by means of 
guy-ropes until the sheave is in a position to hoist the 
panels and hold them while being secured in place. 


Order of Stripping 


Thought must be given to the order of stripping forms, 
whether built in place or made in panels. In the first case, 
it is primarily in the erection that consideration should be 
given to the order of stripping; forms should be so con- 
structed that it will not be necessary to break the lumber. 
Ordinarily, the order of stripping will be the reverse of 
that in erection, unless, in the case of panel forms, it is 
desired to reuse certain panels in advance of others. If 
possible, it is desirable to schedule removal of panels so 
they can be removed and reset in one operation. Detailing 
of forms to make stripping easy will be discussed in fol- 
lowing sections. 


DETAILING 


HE job procedure having been planned by analyzing 

thoroughly the various considerations, the next step is 
to detail the forms. Architects occasionally require that 
form details be submitted for approval in much the same 
manner as steel shop drawings. When not required to do 
so, the contractor can usually save time and money for 
himself by preparing key or assembly drawings and large 
scale details of the various parts. These drawings are given 
to the bench carpenters and to the foreman in charge of 
the erection crew for construction purposes. They are also 
very useful when ordering material. 


The Panel Job 


If panel forms are to be used for an entire job or a 
major part of it, a key drawing showing location of panels 
of the same size and shape is indispensable. Such a draw- 
ing need be only a skeleton or outline drawing without 
details and generally without dimensions. Architect’s 
drawings of the building elevations may be used simply by 
outlining panels in their respective locations. Each panel 
should be given an appropriate mark to signify those 
having the same dimensions and details. By means of sub- 
scripts, or other identifying numbers, the order in which 
each panel is to be used can be indicated. If the architect’s 
drawing contains so much detail as to make it difficult to 
use as a key drawing, a tracing can be made showing the 
principal outlines which will define the divisions between 
panels. Figs. 17 and 21 are typical key drawings for panel- 

form jobs, except that more detail than necessary is shown 
to illustrate certain points discussed in the preceding 
section. 

A detail drawing, such as Fig. 25, should be made of 
each panel and only one panel shown on a sheet, except 
that rights and lefts may be called for on the same sheet. 
The detail should bear the mark number corresponding to 
the key drawing, and the number of such panels required 
should be shown. All essential dimensions must be given 
so that bench carpenters or mill men need not refer to the 
architect’s drawings. The spacing of studs and/or cleats 
should be given, and the number of boards required for 
sheathing should be shown if ordinary lumber is used. For 
the average job, it is not necessary to give a distinguishing 
mark to each piece of lumber making up a panel, because 


SECTION 6 


the mill man or his helper will select from stock the ma- 
terial required. He will do the necessary ripping and cut- 
ting and will then turn over the material with details for 
panels of a certain mark to the bench carpenter for 
fabrication. 

On an exceptionally large job, it is desirable to give all 
pieces a mark. The mill man then prepares the material 
according to a list furnished him by the route clerk. The 
labor foreman bundles and labels the number of pieces of 
each mark required for a certain form and delivers the 
bundles to the bench carpenter who, in turn, fabricates the 
panels in accordance with details given him by the route 
clerk. 


JOB NO.110 PANEL MK.A 


No. Required 


BILL OF MATERIAL | 
10-Wanted as shown Mk. AL No.Pc.| size |Length|stock 
ear ecener ie Fale ol deel 

100] 1x6") 6-2} 

60] Ix") 3°95" 

20] I"x4"} 2-04. 


=r jaftes 


ig 20) 


21 


WW 


LAY 


RY 


ky 


Fig. 26—The south or planetarium tower, Griffith Observatory, Los 
Angeles, reflects in the sharp details the value of careful form design 
and construction. Austin and Ashley, architects; Wm. Simpson 
Construction Co., contractor. 


On each detail sheet there should be a lumber schedule 
listing the number of pieces required, their sizes, lengths, 
and mark numbers if individual pieces are marked. Know- 
ing the number of panels required for the job, the total 
amount of lumber required for the panel forms can be 
determined readily, Wales, braces, kickers and lumber for 
built-in-place forms must be estimated separately. 


The Built-in-Place Job 


Key drawings for a job in which most of the forms are 
built in place are usually the architect’s large-scale draw- 
ings supplemented by such other drawings made by the 
contractor as may be necessary to show fully the form con- 
struction. It will usually suffice to show only sheathing, 
wood molds and plaster molds in direct contact with the 
concrete. If the studs at corners, reveals and other places 


SS 
as 
een, eee 
\ Q : te te f 
Y fol __foapardl ; 
fe) 
7S re i 
| 0 a 
Q Gir 4 
3) 
s > 
ae 4 6 
\ J : c ¢ 
() S w “s 
Q i. a B 
iS = Lt 
ae i 
: g Q 23 | at 
Plaster — ] 
pate Eee 
| te 
‘ wal L IL 
SECTION ON LINE A-A I 
B 
og & 
cas PART ELEVATION OF FRIEZE 
S AROUND BUILDING 
cl F 
3S Beveled strips nailed to forms from 
Se, outside with double headed nails. 
i Leave in place when forms are 
° stripped to be removed later 
ley 
[oy 
on Ss 
ies a 
ae Re 
Sei Saw cut ~ 
ie ce: =| < 
— 
ree BevelstripS 3a 
‘2 slightly ry 
S “| 
ne S 
8 sof 
SS "x6" D.EM Use double headed 
St s Sheets nails here 


SECTION ON LINE B-B SECTION ON LINE C-C 


Fig. 27 


where a more or less complicated arrangement is necessary 
are shown, it will facilitate erection and stripping. Wales 
and ties need not be shown, as a rule, although to doso will 
save time on the job by relieving the foreman and work- 
men of all but the mechanical operation of form erection. 
The maximum spacing of studs, wales and ties should be 
mentioned on the drawings. 

All drawings must be fully dimensioned, except that de- 
tailed dimensions need not be given for waste molds to be 
cast from approved models. Overall dimensions of waste 
molds should be shown to enable the mold-maker and 
carpenter foreman to lay out their work on the same basis. 

Fig. 27 is a typical key drawing. The elevation repre- 
sents the architect’s drawing of the frieze shown in Fig. 
26. The sections may be the architect’s drawings on which 
the forms have been drawn by the contractor, or they may 
be prepared by the contractor expressly for the purpose of 
showing the form construction. 


SECTION 7 


KINDS AND GRADES OF LUMBER AND WHERE USED 


RACTICALLY all formwork, regardless of what may be 

used as the contact surface with the concrete, involves 
the use of lumber. The quality of the finished job is de- 
pendent to a considerable extent upon the kind and quality 
of lumber used. Any lumber that is straight, structurally 
sound and strong and thoroughly seasoned may be used, 
although the softwoods or the woods of pine or fir are 
generally used. The softwoods are usually lighter in weight 
and are easier to work, though not all species are softer 
than some of the so-called hardwoods. Because of the wide 
distribution and abundance of the softwoods they are 
the most economical for all kinds of formwork. 


Kinds of Lumber 


Longleaf Southern Yellow pine and Douglas fir, some- 
times called Oregon pine, are widely used in structural con- 
crete forms, and are equally suitable for architectural 
concrete. They are easily worked and are the strongest in 
the softwoods group. Both hold nails well and are durable, 
qualities which make for economy by allowing maximum 
reuse. They are used for sheathing, studs and wales, and 
Douglas fir is used to some extent for milled wood forms. 

Douglas fir is appreciably lighter in weight than South- 
ern pine. It is a little softer, and consequently slightly more 
desirable. The choice between the two should be primarily 
one of cost, as there is little difference between them. 

California redwood is used to some extent for structural 
- concrete forms and is an excellent material for many uses. 
It is not recommended for architectural concrete work, 
however, because of its tendency to stain the concrete. 
Even for studs and wales, redwood is not suitable as the 
stain may drip onto an exposed surface when the wood is 
wet. 

West Coast hemlock is comparable to Douglas fir as 
form lumber and may be used wherever Douglas fir or 
Southern pine is used, although it is not quite as strong, as 
indicated by the safe working stresses given in Table 1. The 
species of hemlock growing on the Pacific Coast should 
not be confused with Eastern hemlock which is not gener- 
ally considered suitable for architectural concrete forms, 
although it is used for structural concrete. 

Northern White, Idaho White, Sugar and Ponderosa pine 
are excellent woods for architectural concrete forms. Since 
they are not so abundant as Douglas fir and Southern pine 
and are used for purposes for which the latter are not so 
well suited, they are not generally economical for forms 
except for special uses. Because the white pines are soft 


and straight-grained, they are especially well suited for run 
moldings and milled forms for ornamentation. The white 
pines stay in place well, as they are not inclined to warp 
and twist. This characteristic is especially desirable for 
forms made up of an assembly of milled pieces, as they 
will remain tight and will insure sharp detailing. Norway 
pine and Eastern spruce have many of the qualities of the 
white pines and may be used, providing satisfactory grades 
can be obtained. 


Grades, Sizes and Patterns of Lumber 


Lumber used for architectural concrete forms, particu- 
larly for contact surfaces, should be of a higher grade, as a 
rule, than would ordinarily be used for structural concrete 
work. This is especially true, where relatively smooth sur- 
faces free from blemishes are desired. In general, No. 1 
dimension and boards, although they cost slightly more, 
are economical because they are straighter and more 
sound and require less labor for construction. More re- 
use. also can be obtained from No. | material than from 
second and third grades. If forms are to be used only once, 
No. 2 dimension is satisfactory for studs and wales, but 
No. 1 boards should always be used for sheathing unless 
an impression of knots and other flaws in the wood is 
desired in the concrete for architectural reasons. 

There is an appreciable difference in the quality of 
various woods of the same grade designation. While almost 
all softwoods are graded in accordance with the American 
Lumber Standards, various regional lumber manufac- 
turers’ associations have drafted grading rules which apply 
to the species produced by their members. Inherent char- 
acteristics of the various woods have been taken into 
consideration in establishing the different grades. When- 
ever No. I or other grades of lumber are mentioned in this 
booklet, they shall be understood to mean the grade desig- 
nation of the regional lumber association of manufacturers 
producing the specie of lumber recommended for the pur- 
pose being discussed. 

Although white pines are not generally used for ordinary 
sheathing or for studs and wales, in some markets they 
may be more economical than Douglas fir or Southern 
pine. If so, the next lower grade than that recommended, 
which is based on Douglas fir or Southern pine, may be used. 

Particular care should be used in the choice of sheathing 
lumber. If the finished surface is to be uniformly smooth 
and to show only a slight impression of joint lines and 
grain marking, No. 1 dressed and matched boards uni- 


23 


Fig. 28 


formly sized should be used. For especially smooth sur- 
faces where a form liner is not used, C-grade vertical or 
flat-grain thoroughly seasoned flooring or select merchant- 
able boards should be used. 

For smooth surfaces, it is essential that tongued-and- 
grooved lumber be used to hold the sheathing in align- 
ment and thus prevent offset joints which would detract 
from the smoothness of the surface. Matching of the 
boards also serves to prevent leakage through the joints, 
which would cause slight fins that accentuate joint lines. 
Fig. 28 illustrates the surface obtained with tongued-and- 
grooved dressed sheathing. 

Sheathing lumber, even though oiled, has some ten- 


Fig. 29—1-in. boards, surfaced two sides and center-matched 
(S2SCM). 


142, 2% 3% AM 5%6 


Fig. 30—1-in. flooring, standard-matched. 


24 


dency to warp or cup. This tendency is more pronounced 
in wide than in narrow boards. Thus, the impression of 
joint lines between boards can be emphasized or reduced 
by selecting wide or narrow sheathing. For average work, 
6-in. boards are used. There is a slight advantage in using 
4-in. boards or flooring where a very smooth surface is 
desired, while 8- and 10-in. boards make the joint lines 
more pronounced because of cupping. 

Labor can be saved by using center-matched boards or 
flooring (Fig. 29) rather than standard-matched (Fig. 30), 
in which the tongue and groove are off center, because it is 
not necessary to turn the boards when applying them to 
the studs. Greater reuse can be had from center-matched 
lumber, because boards can be reversed if one side be- 
comes damaged. It is also an economy to order sheathing 


28 5%, 1%, Ye 18 


nar 


25, 


Fig. 31—1-in. shiplap boards. (In some woods the lap is Y-in. wide). 


lumber loose run, as less labor is required to draw the 
boards tight, especially after the first use, because the 
swelling of the lumber may make the tongue larger than 
the groove unless this precaution is taken. 

Shiplap (Fig. 31) is used to some extent in place of 
tongued-and-grooved boards for sheathing. It is not quite 
so desirable for the smoothest surfaces, because there is 
more tendency of the boards to offset slightly. A little 
more reuse can sometimes be obtained as there is less 
chance of splitting the edges when stripping. 

Rough-textured surfaces that show pronounced grain 
marking and joint lines between form boards, as illustrated 
in Fig. 32, are obtained by using re-sawed square-edged 
lumber. For a surface showing only mild accentuation of 
joint lines, No. 1 boards surfaced one side and two edges 
are used, and the rough side of the lumber is used as the 
contactsurface. Surfacingof edges is necessary to straighten 
the boards so they can be drawn tightly together. Dressing 
one side reduces variations in thickness so that the offset 
between adjoining boards is not so great. For very rugged 
textures, neither side of sheathing should be surfaced. The 
grain of rough lumber will show plainly in the finished 
concrete even though raising of grain is prevented by oil- 
ing the forms. If it is desired to have the grain marks more 
pronounced, the grain can be raised by wetting the lumber 


before oiling. A still more effective method is to spray the 
sheathing lumber with ammonia. The rough-textured sur- 
face obtained from forms treated in this manner is appro- 
priate for certain styles of architecture and provides an 
especially good bonding surface for stucco. 

Lumber used for backing lining materials need not be as 
high grade as that used for contact surfaces. It is necessary, 
however, that the sheathing lumber be sized to uniform 
thickness, and 7 and G material should be used to prevent 
offset joints if a lining material less than 14 in. thick is used. 
If square-edged or rough lumber is used for backing, the 
joint lines may show through, especially in bright sunlight, 
due to slight shadow lines. Wide boards accentuate this 
effect due to cupping, just as in surfaces formed in direct 
contact with the form boards. Since it is usually the pur- 


Fig. 32 


pose of a form liner to obtain the smoothest possible 
surface, every precaution in selecting backing material 
should be taken to avoid impressions of the boards show- 
ing in the finished concrete. Near the ground or at places 
of close observation, it is advisable to use 1x4 flooring for 
sheathing to minimize cupping, particularly if 4-in. thick 
lining material is used. Knots, shakes and checks, if not 
sufficient to weaken material greatly, are not particularly 
objectionable in boards for backing, so No. 2 and No. 3 
grade lumber are usually satisfactory. 

As previously stated, the soft, close-grained woods, such 
as the Idaho, Ponderosa and Sugar pines, Norway pine and 
Eastern spruce, are best suited for run wood moldings and 
other milled forms. This lumber should be free from pro- 


nounced defects which might mar the perfection of detail 
desired. Grading rules vary somewhat and the various 
grades of white pines are higher than similar grade desig- 
nations in Douglas fir or Southern pine. For average milled 
forms, however, nothing lower than No. 2 grade material 
should be used. For quite fine, intricate detail, No. 1 
grade should be specified to secure material more free from 
knots and other slight defects. 

All lumber for forms should be well seasoned. This is 
especially true for milled forms in which an assembly of 
pieces is used, for the precision with which the various 
parts fit together determines the sharpness and perfection 
of the finished detail. Shrinkage, caused by drying after 
forms are erected, is quite rapid and causes joints between 
boards to open if green lumber is used. Even with the best- 
seasoned material, if forms are exposed to the sun several 
days before placing concrete, the joints may open enough 
to permit formation of small fins. When this occurs, the 
forms should be wet a day or two before concreting to 
tighten the joints; otherwise pointing with water putty or 
similar material may be necessary. If forms must be wetted 
to swell the wood and close the joints, special care should 
be given to inspection to be sure they have not been 
thrown out of alignment by expansion and contraction. 


Plywood 


Plywood designed for formwork is made of high grade 
Douglas fir and has all the desirable qualities of that lum- 
ber for such use. The sheets are clearly marked on the 
edges to identify the material as concrete form grade. Such 
plywood is made with waterproof glue. The common 
grades of plywood used for interior construction where it 
is always dry are not suitable for formwork. Since ply- 
wood is made up of three or more laminations of thin. 
sheets of wood in which the grain in successive layers is at 
right-angles, it is quite warp-resistant and will not split, 
which greatly increases its reuse. Plywood that is oiled or 
treated at the mill and then retreated on the job before it is 
used will give better service than when it is treated on the 
job only. Better penetration is obtained, and raising of the 
grain, separating of the plies and excessive checking are 
more effectively prevented. 

Plywood may be had in thicknesses of 4, 3%, %, 54 and 
34 in. Except for curved forms, the ¥- and 34-in. thick- 
nesses are most commonly used for formwork. 

Any width of sheet desired up to 48 in. can be obtained 
from the mills, although frequently only the 36- and 48-in. 
widths are carried in local yards for quick delivery. 
Sheets 48 in. and under are given the base price. For the 
sake of appearance, two widths should never be used 
where one will do, unless the architectural design requires 
a certain arrangement of joint lines. Fig. 34 shows the 
result of using odd-sized pieces of plywood and joints not 


25 


properly made. Fig. 33, on the other hand, shows the 
pleasing effect obtained by using sheets of uniform size 
and by exercising care in the making of tight, smooth . 
joints. ee 

Plywood, at the base price, is made in standard lengths : 
up to 8 ft., the most common length used for form-work. 
Longer lengths up to 12 ft. may be obtained from the mills, 
but a premium must be paid. 

The 14-in. and 3%-in. plywood have 3 plies. Heavier 
panels have 5 plies. Plywood thinner than % in. requires 
a backing to prevent deflection that would be noticeable 
in the finished surface. The 4-in. and 34-in. thick sheets 
must be backed up solidly, otherwise the deflection be- 
tween sheathing boards will be noticeable. It is usually 
more economical to use the 5-in. or thicker material 
without backing than to use the thinner material with a 
tight backing, except where the architectural detail re- 
quires cutting the form material into small pieces and 
precludes reuse of the lining. The 14-in. plywood is useful 
for curved surfaces. It can be bent to a 3- or 4-ft. radius 


without steaming and to a smaller radius if steamed. The 
Fig. 33—Plywood form lining was used in such widths as to bring all joint labor involved to force plywood into a shorter-radius 


lines to level planes and to principal lines in the design. Venice High curve and the difficulty of holding it is not warranted. A 
School, Venice, Calif.; Austin and Ashley, architects; Clinton Con- 


struction Co., contractor. 


simpler method of forming short-radius curves is described 
elsewhere. When thin plywood is bent, it may be used 
without tight backing, but the supports should not be 
farther than 10 or 12 in. apart. 

For built-in-place forms in which 44-in. and %-in. ply- 
wood is used, the plywood should be nailed at about 8-in. 
intervals along all four edges with 3d blue shingle nails. 
These nails are small enough to permit easy stripping with- 
out damaging the plywood, but have adequate holding 
power to secure the lining in place. It is desirable to nail 
the lining with at least one nail to every square foot 
throughout the surface to prevent any tendency to bulge. 
The edges of abutting sheets should be nailed to the same 
backing board to insure a smooth joint. Where forms are 
built in panels for repeated use, a somewhat closer nailing 
is desirable or else slightly larger nails should be used to 
reduce the amount of repairing necessary to keep the 
panels in good condition. 

Plywood 5%-in. thick and heavier is used without back- 
ing, the plywood being nailed directly to the studs. The 
load-carrying capacity of plywood is considerably greater 
when the span is in the direction of the grain of the outside 
plies; hence the deflection will be materially less if the 
studs or other supports are at right-angles to the grain of 
the outside plies. The studs should not be spaced farther 
apart than 16 in. for 34-in. plywood and not more than 
12-in. centers for 5-in. material. When the grain of the 
plywood is parallel to the studs the spacing should be 
reduced 2 in. for all thicknesses of plywood. 

Whether forms are built in place or in panels, the joints 
between sheets of plywood which are parallel to the studs 


26 


must be made directly over a stud. This is the obvious 
thing to do when forms are built in place, but the impor- 
tance of it is sometimes overlooked when using panels. A 
method of detailing panel forms to secure good alignment 
and inconspicuous joints is illustrated in Fig. 35. Panel 1, 
of which Stud A is the edge stud, is first set in position. 
The plywood sheathing of Panel 1 laps over Stud 4 only 
to the center, leaving the other half to receive the edge of 
the sheathing of Panel 2. Stud B, which is the edge stud of 
Panel 2, is 14 to V4 in. less in depth than Studs 4 and C. 
The 1x6 cleat bears against Studs A and C and is nailed 
with a double-headed nail to Stud B. This will draw the 
sheathing of Panel 2 snugly against Stud 4, making a very 
inconspicuous joint provided the plywood has been cut to 
a smooth, straight edge. The sheathing of Panel 2 is not 
nailed to Stud A, so the panels can be stripped simply by 
removing wales and 1x6 cleats. 

Plywood can be cut with a hand- or power-saw and if 
a fine saw is used, a sufficiently smooth edge can be made 
to make dressing with a plane unnecessary for most work. 
For the very finest job, it is advisable to smooth and 
straighten sawed edges with a plane. After the forms are 
erected, slight irregularities in alignment of abutting 
sheets of plywood can be removed with a block plane. 
Small wooden wedges may be driven between the plywood 
and the stud at a joint to bring the sheets into good align- 
ment as shown in Fig. 36. Note that the studs are horizon- 
tal and the wales vertical in this example, although it is 
customary to run the studs vertically and the wales 
horizontally. The grain of the plywood runs vertically in 
this case, so as to take full advantage of the strength of the 
material. Pieces of 2x4 are placed between the studs for 
headers at the vertical joints in the plywood to provide a 
firm backing to which the edges of the plywood are nailed. 


Plastic Surfaced Plywood 


Some plywood manufacturers produce phenolic resin- 
surfaced plywood which is being used by many contrac- 
tors. The surfacing is applied at the factory under heat and 
pressure and creates a very smooth, hard, water-resistant 
surface on the plywood which will withstand considerable 
abrasion. The bond between the plastic surfacing and the 
plywood core is as strong as the bond between the plies in 
plywood itself. Because of its high resistance to water, 
raising of surface grain on the plywood is prevented. The 
resulting concrete surface is very smooth and free of any 


Panel 2— 


grain marking. It is claimed that when it is handled with 
reasonable care at least double the number of reuses can 
be obtained with plastic-surfaced plywood than with plain 
plywood. The number would, of course, be influenced by 
the manner in which it is used, particularly whether it is 
used as sheathing nailed to studs or in panels that would 
require little remodeling. 

Plastic-surfaced plywood is available in the same sizes 
and thicknesses and is used in exactly the same way in form 
construction as the plain plywood. It is oiled or is given 
other form treatment before each use but because of its 
impervious surface considerably less of the oil or treatment 
will be used. The plywood manufacturers’ directions for 
oiling or other treatment should be followed for best re- 
sults. 


Tempered Fiberboard 


Fiberboard is used as a form liner where smooth sur- 
faces entirely free of grain marking are desired. It is made 
of shredded wood chips compressed under very heavy 
pressure at a high temperature. The board is treated to 
minimize absorption. This process is called tempering and 
only the tempered board of concrete-form-board grade 
should be used. Wherever fiberboard is mentioned in this 


27 


booklet, it shall be understood to refer to board of this 
grade. 

The face surface of tempered fiberboard is very smooth 
and when new has a semipolish. 

In general, fiberboard is not used as a liner for panel 
forms because of the difficulty of making tight joints. 
Except where the width of a single panel will reach from 
one reveal to another, or between some other lines in the 
architectural treatment, it is advisable to build the forms 
in place or to attach the lining to panel forms, being sure 
that the joints in the fiberboard do not come at the joints 
between panels. 

Tempered fiberboard is manufactured in two thick- 
nesses: 3-in. and 14-in. The sheets require a tight backing 
for architectural concrete. An impression of the backing 
boards which detracts from the appearance of the building 
will show in the finished surfaces (see Fig. 37) unless the 
boards are placed tightly together. 

Sheets of two sizes are manufactured, namely, 4x8 ft. 
and 4x12 ft. As delivered, the edges are straight and the 
corners square. The usual procedure is to erect the face 
form and then nail the fiberboard to the sheathing. 
Wherever possible, full-width sheets should be used. 

The edges of adjoining sheets should be nailed to the 
same backing board, otherwise the joint will be more pro- 
nounced because of a slight offset. Three-penny blue shingle 
nails or other nails with thin flat heads and a thin shank 
should be used. The edges of sheets should be nailed at 
6-in. intervals for 3-in. board and not more than 8 in. 
apart for the 14-in. board. There should also be at least 
one nail to each square foot of surface over the entire 
sheet. 

To prevent buckling, joints should be left just wide 
enough to permit a dime to be thrust between the abutting 
edges. These joints must be filled with patching plaster, 
cold-water putty or a mixture of equal parts of beef tallow 
and portland cement to prevent leakage. A light sanding 
with No. 0 sandpaper will make the joint smooth and 


28 


practically invisible. 

The backing boards should never be more than 6 in. 
wide; 1x4 dressed and matched lumber is best because it is 
less likely to cup. Care must be exercised to have the back- 
ing in good alignment, and free from bulges and irregular- 
ities, since they show plainly in the finished surface even 
though a form liner is used. 

Fiberboard may be cut with power- or hand-saws, but 
the best work can be done with a power-saw having an 
88-tooth, 10-gage blade, 14 in. in diameter for straight 
saws, and an 8-13-8 gage for miter-ground saws. To avoid 
rough joints, any burrs on the edges should be removed 
with a block plane after the lining is nailed to the backing. 

When drilling for tierods, use a worm-center bit to avoid 
tearing the fiberboard and drill from the face-side of the 
form. This will very largely prevent any burr around the 
hole, but if a slight burr is made, it should be removed 
with fine sandpaper. The fiberboard should be tight against 
the backing at all places, particularly where it is drilled 
for tierods. 

Fiberboard should not be too dry when used. To be sure 
that it contains some moisture, the sheets should be wet 
on the back side at least 12 hours before being used and 
should be stacked back side to back. 


Reuses 


Reuse of form lumber depends upon a number of fac- 
tors and the individual job must be considered when 
preparing an estimate. Details and irregularities of walls in 
some jobs may make any appreciable reuse of material 
impossible. Small buildings must often be formed very 
largely at one time, and thus will require enough lumber to 
form the complete job. Even on large jobs where some re- 
use of material can be made, the scheduling of the work 
will affect the number of reuses. On the average job, 
however, a considerable reuse of form lumber is possible 
if care is given to planning and detailing. Exact rules can- 
not be given but experience offers a guide to the estimator’s 
judgment. 

About two reuses of No. 1 Douglas fir or Southern pine 
sheathing may reasonably be expected, provided the job 
is of sufficient size and the construction schedule will 
permit. If most of the job is formed with panels that re- 
quire little alteration, three or four reuses can usually be 
obtained. Sheathing lumber used as backing for form 
liner can generally be used twice as many times as when 
used for contact surfaces. 

For built-in-place forms about 6 or 8 reuses of form 
grade plywood are not unreasonable to expect if care is 
taken in its handling. A greater number of reuses should 
not be expected ordinarily for architectural concrete work, 
since the surface of the board will become so marred as to 
make it unserviceable although still strong and satisfactory 
for structural concrete forms. 


Plywood having a plastic surfacing applied at the fac- 
tory may give double the number of reuses of plain 
plywood. 

About 3 or 4 reuses of fiberboard are the maximum that 
can be expected when used as a liner for built-in-place 
forms. 

If panel forms are used with no changes or only minor 
alterations between reuse, 50 to 100 per cent more reuse of 
any sheathing or lining material can be obtained than in 
built-in-place forms. This estimate would give as many as 
4 reuses for sheathing lumber, 16 for plain plywood, 32 for 
plastic-surfaced plywood and 8 for fiberboard in panel 
forms. As stated previously, however, the number of 
reuses will depend on many factors which vary from job to 
job. 

On the average job, sufficient dimension material should 
be provided for one complete set of forms and 15 to 20 


WOOD MOLDS 


HE choice of wood or plaster molds to form architec- 

tural concrete ornament is dependent upon the type of 
ornament, the amount of repetition and, sometimes, upon 
the ability of the local mill or ornamental plasterer to pro- 
duce the required molds. Wood molds are made of white 
pine, soft vertical-grain Douglas fir or other soft wood run 
to size and shape in a commercial mill, or in the job mill if 
the job is large enough to warrant installation of the neces- 
sary shapers. Wood molds are best adapted to ornament 
consisting of simple moldings, combinations of moldings, 
or shapes that can be made with a band saw. Detail involvy- 


per cent additional allowed for breakage and waste. This 
quantity should be adequate for the entire job. 

The grade of lumber has an important influence on the 
number of reuses that may be obtained. No. 2 and No. 3 
grade lumber, if permissible as far as the quality of the 
finished job is concerned, can seldom be reused except to 
a limited extent for studs, wales and braces, or for sheath- 
ing for lined forms. Generally, it is unwise to figure on 
more than one-half as much reuse of No. 2 lumber as of 
No. 1 and not more than one-third the reuse of No. 3 
grade as of No. 1. 

Detailing forms to facilitate stripping without breaking 
the lumber will materially affect the number of reuses 
obtainable. By careful stripping, much needless damage to 
material can be prevented. Proper cleaning and prepara- 
tion of lumber for reuse are also important. The subjects 
are more fully discussed in other sections. 


SECTION 8 


ing carving or undercuts should be formed with plaster 
waste molds. Wood molds are easier to erect and strip than 
are plaster molds. Less work is required to prepare them 
and less care in handling is necessary. It is therefore advis- 
able to use wood molds wherever possible, resorting to 
plaster molds only when the detail cannot be formed in 
other ways. Figs. 38 and 39 show buildings involving 
types of ornament best formed with wood molds. 

Joints in wood molds should be tight enough to prevent 
such leakage of mortar as would make objectionable fins. 
Wherever possible, at corners and elsewhere in the assem- 


Fig. 38—Ornamentation at the 
cornice and below the first floor 
windows and the fluting between 
windows were formed with wood 
molds. Either wood molds or 
plaster molds can be used for 
lettering as shown. Clearwater 
County Courthouse, Bagley, 
Minn. Foss & Co., architects ; 
A. Heddenberg & Co., Inc., 
contractor. 


29 


be joined where there is no return or reveal, use tongued- 
and-grooved or shiplap lumber or spline the joints. 
Square-edged butt joints are satisfactory for moldings 
applied to a solid backing. 

If several pieces are required to make a complete mold, 
as for a cornice or belt course, the joints in the different 
members should be staggered. By so doing, the mold will 
be more rigid and less likely to get out of alignment. A 
better appearance is obtained by breaking the joints, 
because the short joints in the various pieces can be 
pointed with water putty, making them practically invis- 
ible, with no distinct breaks in the continuity of the design. 

Much time can be saved in erecting and stripping forms 
for a detail involving many pieces of run moldings, if 
brackets are made in the mill to a template to fit the 
general profile of the detail. The section in Fig. 40 illus- 
trates this point. Studs for the wall forms are cut off at line 
X-X. Brackets consisting of pieces 4, B and C which have 
been assembled in the mill are scabbed to the studs. Wales 
bearing on piece A and the lower half of the wale bearing 
on piece C are put in place to hold the brackets, which are 
spaced at about 16-in. centers, in alignment. The cornice 
members are then applied. Pieces 1, 2, 3 and 4 are mold- 
ings and all other pieces are ripped to size from stock 
lumber on the job or in the mill. Note the sawcuts in backs 
of moldings to prevent warping and wedging which might 
result in broken edges. Fig. 41 shows an alternate method 


Fig. 39—The plain, flat wall areas produced by plywood forms on this 
building are relieved by simple ornamental details at the coping, around 
windows and at corners. These details were easily formed with wood 
molds. Callahan County Hospital, Baird, Tex. C. R. Gaskill, Jr., 
architect. 


bly of the various members of a wood mold, make the 
joints by overlapping the pieces as illustrated in Fig. 40 
rather than by butting or mitering them. Slight movement 
due to alternate swelling and shrinking will not open the 
joints if they are made in this way. When members must 


Construction joint —— 


sal ect 
Fro +-4 Ne 
ELSA : ‘ ° 10 ae 
Gh Oe See 
+ba . sie (a Do 
=e S P21 po at 
GL es 
Wye west : J 9 
ae (5) Woe 
Fe a J D 
j . iD a) 
Fake es = 
i Fae ra 
Double headed nails > sw va) 
sb Sa 2 
J sf { x 
Saw cuts near edges "Dh icine ] 
and center of molds : 
to prevent warping —— a 


x6: Sscab-——j-= 


30 


of forming the same detail which, though not quite as 
quick to erect, is substantial and will produce good results. 

No matter how carefully oiled, all wood tends to swell 
slightly when wet. Account must be taken of this fact when 
detailing and building wood molds, perhaps even more 
than for straight wall work, because of the possibility of 


Construction joint. 


2'x4" Braces 


2"x4" Studs 


2"x 4" Studs 


Fig. 41 


breaking corners of the detail if the molds swell and bind. 
Thick, wide molds swell and warp more than thin, narrow 
ones, so it is advisable to use the thinnest material from 
which the various pieces can be run. As a rule, nothing 
thicker than 2-in. material should be used. If thicker 
material from which to cut some irregular-shaped piece 
should be necessary, it is better to divide the member into 
two or more pieces so that thinner material can be used. 
When thick material must be used, one or more saw-cuts in 
the back of the mold will help prevent warping and will 
allow enough “play” or spring so the mold will not wedge 


PLASTER WASTE MOLDS 


Ornamental detail in architectural concrete involving 
floral designs, interlaced or pierced tracery, human forms, 
warped and intricately curved surfaces is generally formed 
in plaster molds. Such molds are called “waste molds” 
because they are broken when stripping and can be used 
only once. The molds are made of casting plaster con- 


<4 
! 
We 
; 
i 
7 
i 
A 
ye 
te 


too tightly because of swelling. Stripping is thus made 
easier and the danger of spalling the concrete is reduced. 

Ornament involving recesses should never be formed 
with perfectly square-cornered pieces unless plaster molds 
are used. The only way wood pieces can be stripped is by 
splitting them out with a chisel, because they will wedge 
very tightly and there is danger of damaging the concrete. 
Wood molds or strips forming recesses should always be 
made with a slight draw or bevel. A wide saw-cut in the 
back of the pieces will also make stripping easier. 


SECTION 9 


taining jute fiber and are reinforced and braced to prevent 
breakage. The type of detail which must be formed with 
waste molds is shown in Figs. 42 and 43. 

The procedure for making waste molds depends upon 
the detail of the ornament. A model is first made in wood, 
plaster, clay or other material. The model is made as a 
“positive” having the same shape as the finished concrete. 
From this model, ‘‘negative’’ waste molds, which are the 
reverse of the finished concrete, may be cast directly, or 
intermediate steps may be necessary, depending on the 
number of waste molds to be made and the detail of the 
ornament. Waste molds are almost always made by orna- 
mental plasterers, the methods used being similar to those 
employed in staff or fibrous plaster work. 

The contractor and ornamental plasterer should confer 
regarding details of waste molds, to be sure they can be 
erected easily and are properly braced and reinforced to 
resist the pressure of the concrete. Molds must be made in 
sections that can be handled easily. If too heavy they can 
be broken in handling. Individual pieces should not weigh 
over 150 lb. to be set without difficulty by two men. 

The thickness of molds will depend upon the detail, but 
should not be less than 1 in. at any place. Jute fiber is 
added to the plaster to strengthen it, but the mold-maker 
should be warned against using more fiber than necessary 
to give the required strength for handling, because an 
excessive amount makes it difficult to chip the mold from 
the concrete. 


Fig. 42—Elaborate detail such as this, whether the same motif is re- 
peated or the ornament is used only once, is always formed with plaster 
waste molds. Entrance to Wilshire Professional Building, Los 
Angeles. A. E. Harvey, architect; L. T. Mayo, contractor. 


31 


Fig. 43—Panels involving human or animal figures are formed with plaster 
molds which are modeled the same as a piece of sculpture. Ector County 
Courthouse, Odessa, Tex. Elmer G. Withers Architectural Co., Inc., 
architect; James T. Taylor, contractor. 


The shape of the back of the mold depends upon the 
detail of the finished concrete. For flat surfaces without 
deep ornamentation, the back side should be made flat to 
bear directly against studs or wales. Fig. 44 shows the 
back of a waste mold used to form a recessed ornament. 
Note the flat surface around the edge of the mold and the 
two flat strips across the back. The flat surfaces are made 
to bear against the form sheathing or a framework of 
studs. The two wood strips are provided for handling the 
mold and are removed before it is set in position. The mold 
is nailed to the supporting timbers with common nails. 
The nail-heads are countersunk and the holes are pointed 
with patching plaster. 


32 


Irregular-shaped molds, or those with very deep relief 
(see Fig. 46), would be too heavy if made flat on the back, 
so the back is made to conform approximately to the shape 
of the front, with the thickness of plaster seldom more 
than 114 or 2 in. Wads of plaster with a liberal amount of 
jute are used to reinforce the model and block it out to 
bear against the form framing. Also, a wooden frame con- 
sisting of 2x2-in. or 2x3-in. pieces to reinforce the mold 
against warping is attached to the back with plaster and 
fiber as shown in Fig. 45. The face or contact side of a 
waste mold like that shown in Fig. 45 is illustrated in 
Fig. 47a. Waste molds are usually delivered to the job 
ready to be assembled in the forms, and the various pieces 
fit together accurately. Slight irregularities may be re- 
moved with plane, chisel or steel wool. The ornament 
formed by the waste mold in Fig. 47a is shown in Fig. 47b. 

Molds for irregular detail, especially where there are 


jenn 
2S. 


a 


Weole 
\ 


tI 
4 


Ld 


Fig. 47a 


undercuts, are often made in several pieces. Setting and 
bracing such molds is simplified if the reinforcing frame 
for the various pieces is built out to a common plane. A 
plane parallel to the line of the wall is convenient because 
the framework of the molds can bear directly against and 
be tied to the studs and wales. Fig. 48 shows the mold for 
an ornamental head jamb of a door opening. The mold is 
made with a flat section parallel to the wall which bears 
against the studs. Jute fiber dipped in plaster is twisted 
about the studs and blocking to secure the mold in place. 

Very small waste molds are not shaped on the back to 
conform to the face. It is evident from Fig. 49 that con- 
siderable labor would be necessary to block out from the 


Studs 


back of such a small mold to a bearing against the form 
sheathing or studs, if the back conformed to the shape of 
the face. By making the mold with a smooth back and 
seat, it can easily be set in the form as illustrated. Such 
molds can be fastened in place by nailing from the face 
into the form sheathing or preferably from the back side 
with double-headed nails. When the forms are stripped, 
the double-headed nails may be pulled and the waste mold 
will be left in place to protect the ornament until the rest 
of the forms are removed and other work in that area is 
completed. This illustration shows the importance of de- 
tailing forms before waste molds are made, so that the 
latter can be made to fit the backing prepared for them. If 
the waste mold-maker is allowed to devise his own details, 
troublesome blocking out and cutting of the backing for 
the molds is often necessary. 

It is frequently necessary to chip the plaster from waste 
mold formed detail, particularly if there are undercuts or 
interlacing detail. For this reason it is desirable to use 
colored plaster for a thickness of about 4 in. at the con- 
tact surface, the color serving as a warning to exercise care 


33 


to avoid injuring the concrete. Fig. 50 shows a waste mold 
formed ornament. At the left of the opening the mold is 
still in place, while at the right side most of the plaster has 
been chipped away. Some plaster still remains in the 
undercuts, indicating the desirability of having a colored 
layer of plaster next to the concrete, since the plaster does 
not break away clean in one piece, but must be carefully 
chipped from around the concrete. 

The smooth finish of cast plaster is not always appro- 
priate to the architectural treatment, especially where it 
would make a surface too smooth in contrast to the sur- 
rounding texture formed with rough boards. To avoid this, 
the surface of waste molds or the model can be tooled or 
roughened with a wire brush. 

It is important that waste molds be held rigidly in posi- 
tion. Wires can be passed through the face of the mold and 
by twisting the wire, the loop will bite into the plaster 
enough to bury itself. Two holes to receive the wire, 
generally 14-gage, are drilled about 2 in. apart using a 
twist-drill just slightly larger than the wire. The cut made 
in the face of the mold when pointed with patching plaster 
will leave no trace of the wire. To further secure waste 
molds rigidly against the supporting studs and wales, jute 
dipped in plaster is twisted about the framework of the 
mold and supporting timbers. 


34 


To make the joint between a waste mold formed area 
and the adjoining forms as inconspicuous as possible, it is 
desirable to make the joining at a slight reveal or angle in 
the form as illustrated in Fig. 51. The natural line in the 
detail obscures any slight irregularity in the joint. Some- 
times the architectural detail requires the joining to be 
made on a flat surface. If so, the waste mold should be 
rabbetted to receive the abutting sheathing. (See Fig. 52. 
Observe that the waste mold is rabbetted at the corner 
when made in pieces.) 

After the molds have been secured in position and the 
forms are aligned and braced, all joints in molds and be- 
tween molds and adjoining forms must be pointed with 
any acceptable nonshrinking pointing compounds. These 
materials are used by mixing with a small quantity of 


Plaster 
waste mold 


Fig. 52 


water until plastic. The mixture is then pressed into the 
joints and smoothed off with a putty knife. When it has 
hardened, fine steel wool or fine sandpaper is used to 
remove any slight roughness. 

Waste molds are usually given two coats of white shellac 
to make them waterproof and nonabsorbent. If this is not 
done, it is quite certain that there will be a difference in the 
color of the concrete as compared with adjoining areas. 
After molds are set in the forms and all patching and 
pointing has been done, any new plaster is shellacked. 
Before concrete is placed, the waste molds must be greased 
to facilitate stripping. This subject will be discussed in 
a later section. 


METAL FORMS AND MOLDS 


Metal forms and molds are used to a limited extent for 
architectural concrete work. Quite pronounced joint lines 
in a regular pattern are characteristic of metal panel forms 
and such joints are generally objectionable in an architec- 
tural concrete job. If the walls are to be stuccoed or 
ground, thereby covering or removing the joint lines, metal 
forms may be used. As a rule, however, the difficulties 
involved in working to window openings, floor heights 
and corners with standard or even special panels offset 
any possible economy resulting from reuse of material and 
the labor saved in erection of straight wall forms. Fig. 53 
shows the pattern effect produced with metal forms. At 
the right is shown the result of using special panels to work 
to a corner. The wall illustrated is below grade, but the 
effect obtained is characteristic of metal formwork which 
is not satisfactory for architectural concrete. 

Special metal molds have their place among architec- 
tural concrete forms. Black iron should preferably be used, 
because galvanized metal may stick to the concrete, leav- 
ing it rough even though the forms are well oiled. Corru- 
gated iron sheets are frequently used, for example, to form 
fluting in pilasters, piers and spandrels. The sheets are 
made with standard corrugations, or special corrugations 
can be had if the quantity of material required is sufficient 
to warrant special rolls. Other special shapes may be used 
economically and satisfactorily if there are a large number 
of repetitions. Plaster or wood molds usually can be used 
for details that can be formed with metal. Metal molds are 
more difficult to erect than those of wood or plaster, but 
the added labor and time required may be offset by a 
‘saving of material if there is considerable repetition. The 
choice of metal molds as compared with other types is 


Fig. 53 


SECTION 10 


Fig. 54—Metal molds were used to advantage in the forming of the curved 
surfaces of the mullions in this building and for the fluting at the top of the 
tower. Wilshire Tower Building, Los Angeles. Gilbert Stanley Underwood, 
architect; H. W. Baum Co., contractor. 


generally a question of economy. 

A typical example where metal molds were used is 
illustrated in Fig. 54. The mullions involve two curved 
surfaces as shown in Fig. 55 while the corner piers at the 
top of the tower are made up of five flutes as shown in sec- 
tion in Fig. 56. The curved surfaces were so detailed that 
standard rolls could be used for shaping the sheet metal 


Return metal 
around corner 


Figs ao 


35 


sore. | a 
fei og. OTK | 
Wsnon Ga lf 
Ae Pa SAU Dy 
Aeon AG AN 
Nail here sire : 
SOsGe 


Wee) 
ef 


Nail here { 
BLOGs 


Collars oer ee #26 Black iron 
|" material 


Collars 9'o.c. 
I" material 


| 
| 
| 
§ 


Fig. 56 


forms thus eliminating the cost of special rolls. The sheet 
metal is stiffened by blocks of wood or collars cut on a 
band saw to fit the shape of the mold. The blocks or collars 
should not be spaced more than 9 in. to 1 ft. apart to pre- 
vent distortion of the metal. The gage of metal to use will 
depend on the size of mold but, ordinarily, 24- or 26-gage 
is satisfactory. Where possible, as in the mullion detail, it 
is desirable to lap the metal around a corner on the outside 
of the sheathing to prevent leakage and to avoid a streak 
on the surface of a slightly different texture that would 
result if the metal were nailed to the face side of the forms. 

It is essential that all sheet metal be cut in the shop ona 
shear to insure straight, smooth edges. Corrugated sheets 
should be cut exactly at the center of a corrugation to 
make a tight joint between the metal and the backing to 
which it is nailed. By making the cut at the center of the 
corrugation, a full-width corrugation is obtained if it is 
necessary to join two sheets. The sheets should always be 
butted together at the joint and not lapped (see Fig. 57). 

The terminating vertical edges of corrugated sheets may 
be cut along the center of a corrugation the same as for a 
butt joint between sheets as shown at the right edge of the 
sheet in Fig. 57. From an architectural standpoint, it is 
usually better to have a slight reveal where the corrugated 
surface joins the plain surface. This requires a filler strip 
along the edge as shown at the left of Fig. 57. The strip is 
milled to the shape of the corrugations. 

When a single sheet is not long enough to make the en- 
tire form, and cross-joints are necessary, the sheets may be 
butted or, if desired, lapped about 4 in. as shown in Fig. 
57. The upper sheet is lapped over the lower one so the 
slight offset caused by the thickness of the overlapping 
metal will not cast a shadow, thereby making the joint less 


36 


conspicuous. Short wood blocks shaped to fit the corruga- 
tions placed behind the lapped joint will furnish a solid 
support to which the edges of the metal can be nailed. 

Both ends of a corrugated metal sheet should not bear 
tightly against finished concrete surfaces, otherwise the 
sheet cannot be removed without damage to the concrete. 
The blocking used to close the ends of the form should fit 
the corrugation snugly and should project ¥% in. above the 
metal as illustrated in Fig. 57. This will prevent the end of 
the sheet being embedded in the concrete and will facilitate 
stripping. 

Metal sheets of any kind used as form liners over wood 
backing must be nailed at frequent intervals to prevent 
slight bulges. Four-penny box nails should be spaced 
about 6 in. apart along all edges and not more than 12 in. 
horizontally and 24 in. vertically throughout the area of 
the sheet. 


Butt joint 


Flush joint 
at edge of 
sheet 


(A) 


Filler block 
projects '%" 


aie metal 
Top of 


metal 


Filler strip 
at edge of 
shee 


Lap top 
sheet over 
bottom 4’ 


Fig. 57 


(c) 


TYPICAL FORMS 


Straight Walls 


Straight wall forms for architectural concrete work pre- 
sent a few problems not encountered in ordinary structural 
concrete work. It is primarily important to remember that 
the concrete surface is the finished surface which is to be 
left exposed. Care must be exercised at all times in con- 
structing forms to insure perfection of corners, alignment, 
texture and detail. 

When the construction of wall forms is started, a plate 
should be nailed to the footing; the plate should be care- 
fully lined as the straightness of the wall will depend upon 
good alignment of the starting plate. This plate is set out 
from the finished face of the wall the thickness of the form 
sheathing. Studs are set on the plate and lightly nailed to 
secure them in place. A 1x4 ribbon nailed to the studs will 
serve to align them temporarily. Braces at 10- to 12-ft. 
intervals are, of course, carried to the ground or to a place 
where they can be secured. The bottom sheathing board 
must be leveled accurately. Since the footing will not al- 
ways be truly level or smooth, it will often be necessary to 
fill out below the first full sheathing board to make a tight 
joint at the bottom. It is not desirable to attempt to shape 
the bottom board to conform to the irregularities of the 
footing. 

An example of a special case, but one which illustrates 
the general principles of the starting of a wall form, is 
shown in Fig. 58. In this instance a rustication was located 
at the water table. The strip used to form the rustication 


Fig. 58 


SECTION II 


Fig, 59 


served also as the plate on which the studs for the outside 
forms were erected. A level starting base was thus pro- 
vided. One row of sheathing was placed at the bottom 
which served as the ribbon to hold the studs in line. The 
frame was temporarily braced to the ground and brought 
to final alignment after all the sheathing was applied. 

Sheathing lumber, even when dressed and matched, is 
not always quite uniform in width. This may cause joint 
lines to get out of level; likewise, irregularities in driving 
up adjoining boards may aggravate this condition. It is 
therefore necessary to check the level of joint lines at fre- 
quent intervals. To do this, lines of levels may be set at 3- 
or 4-ft. intervals vertically. The lines can readily be fol- 
lowed by the carpenter if they are marked on the studs 
about every 10 ft. horizontally. It is also convenient to 
mark off a stick into divisions equal to the width of the 
sheathing to be used in checking the level of the joint lines 
as the building of the forms progresses. 

Accurate alignment of architectural concrete forms is 
absolutely necessary. Any amount of care exercised in 
securing good alignment is time well spent. One method 
for aligning a long section of forms is to set points about 
30 ft. apart on the floor with a transit. These points may 
be set back from the face of the wall 3 or 4 ft. to be well 
out of the way. Control-points at the top of the wall 
opposite the transit-points are then accurately set by 
plumbing up from the floor-points and measuring over to 
the wall. Intermediate points are set from a chalk-line 
strung between the control-points. Aligning of forms 
should be done only when there is little wind. If a favor- 
able time cannot be found, then control-points set much 
closer together will aid in alignment. 

Well constructed forms are economical. Fig. 59 is an 


37 


t 


| Double wales ——— 


Double wales ———— 


‘| 4'x4" Studs at pace 
i | plywood joints i 


| 


Se 


Double 2"x6" liners 
at 8 tol0 ft. centers ———> 


Double wales ————>— 


ee 


Wedge 


[sea 


NeSESI 


[ 


Fig. 60 


example of such forms. In this case plywood is used as 
sheathing with the grain horizontal. To provide ample 
space for nailing and to insure alignment and support of 
the vertical joints they are backed up with 4x4 studs spaced 
4 ft. apart. Between the 4x4’s are 2x4’s on 16-in. centers, 
all of which are in turn supported by double 2x6 wales on 
about 24-in. centers. To maintain good vertical alignment 
in a multistory building or a high wall, such as that shown, 
double 2x6 wales are also run vertically at 8- to 10-ft. 
intervals. Note also that the horizontal joints between the 
plywood sheets are backed up with short pieces of 2x4 
between the studs. Fig. 60 shows, in section, typical details 
of straight wall forms. Sheathing is sometimes run verti- 
cally, if the form is to be lined with fiberboard or thin ply- 
wood, and occasionally for special architectural effect. 

Wall forms must be securely tied at corners so they can- 
not move. A slight opening of a corner will cause bleeding 
that may result in sand streaks and will produce an irregu- 
lar line and fin that cannot be satisfactorily removed or 
covered over. One method of making a tight corner is 
shown in Fig. 60. The wales overlap and two vertical kick 
strips are provided at the intersection against which the 
wales are wedged to tighten the corner. In another method 
the wales extend only a little beyond the corner studs and 
are tied together by a tierod placed diagonally across the 
corner. 

Sometimes “log cabin’”’ corners, as illustrated in Fig. 62, 
are used and are satisfactory. The corner can be held tight 
by this method. Note the kick strips in back of the inter- 
laced sheathing boards which prevent any movement. This 
type of corner is more troublesome to build and more 


38 


labor is required for both erection and stripping than for 
the corner shown in Fig. 60 or 61. 


Round Corners 


Rounded corners of radius greater than 4 ft. and curved 
walls can be formed with plywood applied directly to 
studs. Ordinary lumber can be used for curves having a 
radius of 18 or 20 ft. but seldom for those of shorter radii. 
The thickness of sheathing will depend upon the radius of 
the curve. As a rule, 14-in. or 34-in. plywood is used for 
curved corners. Corners having a radius less than 4 ft. are 


Fig. 61 


Fig. 62 


best formed by constructing a solid backing over which 
3-in. fiberwood is applied. 

A typical detail of a form for a long-radius curve, not 
Jess than 20 ft., using plywood sheathing, is shown in 
Fig. 64. The studs are vertical and are blocked out from 
yokes or frames which are spaced 4 to 6 ft. apart ver- 


tically. By staggering the frames to break joints, a full 
circle or any part can be held rigid. Note that for the 
outside form it is necessary at the center of the frames 
and for a distance of two or three studs each way to tie 
the studs to the frames to prevent the spring of the 
sheathing from pulling it away from the frames. For the 
inside form it is necessary to tie the studs at the outer 
ends of the frame instead of those at the center. 

A method of building a round corner form for a curve 
of 4 ft., or greater, radius is shown in Fig. 63. Horizontal 
segmental ribs are spaced about 12 in. apart. Quarter- 
inch plywood with the grain running vertically is applied 
to the ribs. At vertical joints, short pieces of 2x4, to which 
the edges of the plywood are nailed, are cut in between 
the ribs. The plywood is nailed at 6-in. intervals along 
the ribs. 

A detail of a short-radius convex corner is shown in 


Space frames 
4'to6' apart 


Fig. 64 


Pig Mey a < BS cag 


Pluwood or presdwood : 


° Loar) 


Space frames 


4' to 6'apart ey 4" 


39 


> 


GY 


Ribs from 2" 
stock-30"o.c. 


yen oO: 10. oS 
or less 9": Oy 10 
Ding 


Fig. 65. Segmental yokes are cut from 2-in. material to 
the required curvature and then spaced about 30 in. 
apart. The backing for the 3%-in. fiberboard lining is made 
of 2x2 dressed strips placed tightly together. Theoretically 
a slight bevel would be necessary on each strip to make 
it fit snugly but the bevel is so slight that ordinary square- 
edged lumber is satisfactory. 

The spring of the fiberboard lining will tend to pull it 
away from the backing unless closely nailed. To be sure 
the lining holds securely, it should be nailed with cigar 
box nails at intervals of not more than 6 in. in each 
direction. 

Fig. 66 shows another detail of a convex corner of 
rather small radius using plywood sheathing. Two sheets 
of thin plywood are used at the corners as they can be 
curved to a smaller radius than a single thicker sheet. 
The two sheets should be carried beyond the springline 


- 


: —+%' Plywood 


2-%" j 
\ Plywood/ 


asad | ae : c é 
eee 


Fig. 66 


40 


to reduce the tendency to pull out and to assist in obtain- 
ing a tighter, smoother joint where these sheets abut the 
thicker sheathing. 

The forms for a concave corner do not differ materially 
from those for a convex corner, as is evident from Fig. 67. 
In either case, because of the radius of the corner, the 
last tie through the straight part of the wall at each side 
of the corner must be set back several feet. Even though 
the intersection of the wales is properly blocked as pre- 
viously described, there might be sufficient deflection of 
the wales to permit corners of the form to open slightly. 
It is therefore desirable to tie the corner with a piece of 
1x4 as indicated in the illustration. 

When the form is stripped, the side wall forms are first 
removed. This permits the circular form to be removed as 
a unit. Before the circular form is stripped, the pencil rod 


Tempered 
fiberboard 
lining 


Cut from 
2"x 10" 


Fig. 67 


ties should be pulled from the concrete. To do this, cut 
the rods behind the outside wales and pull the rod toward 
the inside of the building with a rod-puller. There are 
two reasons for removing the ties before the form is 
stripped—the form protects the concrete against possible 
spalling and guides the rod; furthermore, if the rod is 
removed first, it will not interfere with removal of the 
circular form as a unit. 


Water Tables 


In the majority of buildings here is a water table at or 
very close to the grade-line which projects slightly be- 


joint 
%' Wee 
16"o.c 


E holes J 


Lap studs 
at least the 
spacing of 
the wales 


Block 
solidly 


yond the face of the wall above. 
A not uncommon detail for a 
water table, except for the rusti- 
cation strips, is illustrated in Fig. 
68. Thestuds from below the water 
table.are carried above the offset 
so that studs for the upper part of 
the wall, which are set in, can be 
securely blocked and tied to the 
lower studs to make the form rigid. The lower studs may 
be in random lengths, so long as they lap the studs above 
by 18 to 24 inches. 

A slightly different water table detail is shown in Fig. 
69. The difference in slope of the two principal surfaces 
makes it necessary to use milled pieces for sheathing in 
order to produce a lap at point A. It is undesirable to 
butt two pieces along such a line, as it will be almost 

impossible to make the joint tight enough to prevent 
leakage. The studs are lapped and blocked in the same 
manner as in the preceding example. 

Water tables sometimes involve shapes not conven- 
iently nor desirably made entirely with wood forms. The 
detail shown in Fig. 70 is of this type. Because of the 


Piece of |"material nailed to 
wale to support sheathing on 
side of pilaster 


Lap studs at 
least the spacing 
of the wales 


Construction 
joint 


Fig. 70 


undercut in the profile, the swelling of a wood mold 
might break the concrete before it has thoroughly hard- 
ened. A plaster mold, which does not swell, for the upper 
part of the detail combined with stock lumber for the 
lower part makes the most satisfactory form. 


Pilasters and Piers 


The forming of pilasters and piers, and often window- 
mullions and reveals, presents somewhat similar prob- 
lems. Generally, the face form for a pilaster or pier can 
be made as a panel, regardless of the form material used. 
Accuracy in the forming of the corners is important, as 
such details are usually a focus of attention in the facade 
of a building. The principal point of observation is gen- 
erally from a position in front of the building. All corners 
must be straight and true and there should be no impres- 
sion of the end-grain of form boards visible in the 
concrete when the building is viewed from the front. __ 

Fig. 71 is a typical detail for a pilaster having a pro- 
jection greater than the depth of the studs. The sheathing 
forming the face should always lap over the corner, while 
the boards forming the reveal butt against the face sheath- 


41 


Double wale 


Fig. 72 


ing. Likewise, the main wall sheathing should butt against 
the reveal, and the sheathing forming the reveal should 
butt against the main wall sheathing. In this way, the 
marking due to end-grain of the sheathing will be on the 
side of the reveal and not visible from in front. Further- 
more, if a slight fin is formed at the outer edge of the 
pilaster, light rubbing with a carborundum stone will 
remove it and the surface will not appear marred. Of 
course, this is only true when there is very little leakage. 
Appreciable leakage should be avoided by making the 
corner as tight as possible. Note that the blocks between 
the main wall wales and the wales across the pilaster are 
made slightly smaller than the spacing they are to fill. 
When the ties are tightened, there will then be no tend- 


Lie FAL 


y-Run sheathing through 
il Shree === 


ency to ride on these outer blocks and the joints A and B 
will be held tight. The sheathing forming the reveal should 
be tacked very lightly to the flat side of the stud in the 
corner. If sheathing is nailed from two directions onto a 
stud, it is very difficult to strip the forms without tearing 
the stud to pieces. 

A very shallow pilaster is illustrated in Fig. 72. In this 
case the projection is only the thickness of the sheathing 
lumber. In order that the wales may extend past the 
pilaster, which is desirable since better alignment and 
security of the forms are obtained, 1x4’s ripped to a 
width equal to the width of the 2x4 studs less the thick- 
ness of the sheathing are nailed with double-headed nails 
to the studs to support the sheathing for the pilaster face. 
This sheathing, whether made up in a panel or erected in 
place, should not bear against the 2x4 studs at each side. 
By allowing a little clearance, stripping is made easier, 
and the face form may be stripped before the adjoining 
studs. 

A typical form detail for a deep reveal involving the 
principles discussed in regard to deep pilasters is shown in 
Fig. 73. 

In the pilaster shown in Fig. 74, it was desired to carry 
the horizontal form board marking continuously across 
the pilasters. This necessitates the use of short pieces 

of sheathing with the studs running ver- 
tically. Since the offsets in the pilaster 
are just the thickness of the sheath- 
ing, the-studs are simply blocked out from 
the wales with pieces of sheathing boards 
to take up the offsets. When the blocking 
behind the studs requires a piece 2 in. or 
more in thickness, it is advisable to use 
larger studs to eliminate blocking. If there 


eee ea eo ep) is considerable repetition of the same de- 
Pee ae |} Do not nail tail throughout the job, it will pay to rip 
aie ae || po ena larger studs to fit the offsets, thus avoid- 


ing blocking. 

It is sometimes difficult to strip forms 
adjacent to deep reveals. This is due to 
swelling of the lumber which causes it to 


freeze against the concrete. Stripping will 
be facilitated by forming such reveals 
with a draw of about 4 in. It is also de- 
sirable, if the sheathing against the reveal 
is assembled with the main form to be re- 
moved as a single panel, to use vertical- 
grain lumber against the reveal rather than 
flat or slash-grain material. The latter will 
swell slightly and tends to bite into the 
concrete. 


Fig. 73 


42 


Spandrels 


Spandrels are often decorative features 
of a building. Sometimes they are highly 


that level to obscure the joint. If 


there is no architectural detail at 
that level, then the entire spandrel 


should be placed with the floor 


slab so as not to have a joint cut 
directly across the face of the 
spandrel. 

If there is a joint at the floor- 
level, the forms for the upper part 
of the sprandrel are not erected 
until the floor concrete has been 


Lap x 
sheathing 


Blocks 


placed. The form shown in Fig. 75 
is satisfactory, whether the upper 


—- 


and lower parts of the spandrel 
are constructed separately or in one 


Fig. 74 


ornamented and require the use of plaster waste 
molds as forms. In general, however, regardless 
of the ornamentation, the method of forming all types 
of spandrels is essentially the same. Most spandrels 
project partly above and partly below the floor slab. 
It is convenient to locate a construction joint at the top 
of the floor as this simplifies concrete placing, provided 
the structural design of the spandrel will permit a 
joint at the floorline. When a joint is so located, 
it is desirable to use some architectural detail at 


aa esfem 
ery Removable “gies 


Blocking 


Plaster waste aA 


mold or wood bys p 
sheathing A 
6 
Uv 
3) 
+ 
Va 8 


pl'x4" 
Temporary + 
support 
) 
ey 
Z os ay 
Extend "T“ head out far °° 
7enough to receive braces va 
“ = a 6 
_ SSS : 


operation. Braces from the ex- 

tended T-head are used to hold 

the forms in alignment rather than 
wires holding the forms back to the floor slab deck as 
is sometimes done. The latter method is not so positive 
in its action. If, for some reason, wires must be used, 
they should be fastened to the outside form high enough 
above the floor to pass over the top of the spandrel so 
they will not be embedded in the face of the wall. 

In order to support the inside form, pieces of 1x4 are 
nailed to occasional studs and rest on the slab forms. 
These supports are removed as soon as the concrete in 
the spandrel and slab has been placed. 


Plaster 
waste mold 
or wood 
sheathing 


‘W 


B 
\'x4" Strips nailed 
to sheathing 


43 


1x4'Strips nailed 
to sheathing 


SILL 
Fig. 77 


Fig. 76 shows a slightly different method of construc- 
tion in that the T-head and diagonal-braces are not used. 
When it is possible to extend the studs past an opening 
and to let the sheathing project at least part way across 
the opening to receive the forms for the window as illus- 
trated, the weight and pressure of the concrete is trans- 
mitted directly to the studs, making other braces and 
shores unnecessary. 


Windows 


Forms for window openings must be made rigid and 
substantial to prevent distortion under pressure of the 
concrete. The box forming a window opening (shown 
in Fig. 77) is best made of 2-in. material, as it is much 
less likely to get out of shape than one made of thinner 
material and the sash will fit properly. Any strips re- 
quired to form the recess to receive the sash, are securely 
nailed to the 2-in. plank forming the frame. The cleats 


Fig. 78 


44 


should be not more than 24 in. apart. If less than 2-in. 
material is used, a closer spacing will be necessary. Cross- 
braces should be located at each cleat horizontally and 
vertically unless there is an inner frame of 2x4’s. Extra 
cross-bracing should be provided in large window forms 
as illustrated in Fig. 78. The frame is supported in the 
form by nailing to the form sheathing. 

Except for windows with very steep sills, it is necessary 
to be able to get at the sill to finish it and to work the 
concrete into place properly. For these reasons, the sill 
of the form may be omitted altogether, as indicated, or 
the sill piece made in two sections for easy removal. 

A circular window-head formed in the same manner as 
a rounded wall corner is shown in Fig. 79. Segmental 
ribs are cut to the desired curvature. Strips cut from 1x2 
or 2x2 stock are applied to the ribs and then plywood or 
fiberboard is nailed to this solid backing. The sides of 
the forms are the same as for a rectangular opening. 

To strip a window form, the cross-braces are first 


Fig. 79 


knocked out. The vertical kick-strips against which the 
cleats bear should then be removed. Next, take off top 
and bottom cleats and wedge out the head, using wooden 
wedges. Do not pry the form loose with a pinch bar, for 
this is certain to spall the concrete. The wooden wedges 
should be driven in at one end, forcing it down and away 
from the side member. To facilitate stripping, a 45 deg. 
cut or miter through the sides of the frame is sometimes 
made when the form is built. 

In general, it is not considered good practice to set the 
permanent window frames in the forms and cast the con- 
crete around them. This usually results in distorted 


2'x4" Cleat 2-O"o.c. 


SJ 


Fig. 80 


Wedge 


y 


2" Block 
spiked to 
horizontal 
stud 


Nail milled pieces 
to blocking to be 
erected as panel 


Assemble at mill 
and set in place 


Wedge 


kere 


1G. 


~~wedge 


Wales continuous across opening 


S 


XS 
2" Block spiked to SP 


Wedge 


horizontal stud 


Fig. 81 


ROPES pe Ku SON PO os eS s 
RES RSS 
4 un sheathing A 
hrough at fal 

OFnMners q = 


frames and badly operating sash. It is also difficult to 
caulk around such frames to make them watertight. 


Doorways 


Forms for door openings do not differ materially from 
those for windows. Because the openings are generally 
larger, somewhat more attention should be given to brac- 
ing and tying the forms to prevent distortion. Unless the 
Opening is extremely wide, it is best to run the wales 
across the opening. The forms can then be kept in better 
alignment and any tendency of the frame to twist can be 
prevented. Workmanlike joining of all angles is espe- 
cially essential in doorways because they are important 
points of interest in the architectural treatment of the 
building. 

A typical method of forming a common entrance de- 
tail is illustrated in Fig. 80. The doorway is recessed by 
several small reveals which may or may not be continu- 
ous across the head of the opening. The similarity of the 
form to that for a window opening is apparent. A sub- 
stantial frame is made with 2-in. plank cleated with 2x4’s 
at 24-in. centers. Kick-strips in back of the cleats are 
nailed securely to the sheathing and the whole frame is 
rigidly cross-braced. The form for the reveal is built up 
as a box and set into the angle between the frame and 
the outside wall form. A row of ties is placed just inside 
the opening to hold all joints tight. 

There are often deep reveals at doorways and the total 
width of the opening may be too wide to warrant carry- 
ing the wales across the opening. A doorway reveal in- 
volving a fluted surface is shown in Fig. 81. An unorna- 
mented surface or an elaborate 
detail requiring plaster waste 
molds may be substituted for 
the fluting shown. The fluting is 
formed with milled wood pieces 
securely nailed to blocking so 
that the panel can be erected in 
one unit and removed as a unit 
+ after the straight wall forms have 
I been stripped. Of course, this is 
K not essential unless the same de- 
eee Selo =e tail is to be repeated elsewhere 
od on 2222S] on the job or the entrance is so 
high as to require more than one 
lift of forms. Note that the 
blocking to which the fluting 
forms are attached is backed up 
by horizontal studs which serve 
X also to tie the main wales 
together, thus preventing any 


x 


45 


ERECTING-OILING-STRIPPING 


OME of the general principles pertaining to construc- 
S tion or architectural concrete forms are so impor- 
tant that they will be discussed in more detail in this 
chapter. Some repetition is also warranted because the 
quality of the job is largely dependent upon the care ex- 
ercised and methods used in erecting, oiling and stripping 
the forms. 


Erecting 


Too great emphasis cannot be placed upon good craft- 
manship. Angles and joints in forms must be made accu- 
rately so that corners will be sharp and straight. Leakage 
through the forms must be prevented or there will be fins 
along joint lines and corners. Miters that are not tight 
and joints between plywood or fiberboard sheets that are 
open enough to allow leakage should be pointed with 


46 


movement of the corner due to deflection of the wales 
which extend quite a distance beyond the last ties. Forms 
for the door opening proper would be made essentially 
the same as shown in Fig. 80. 


Parapets 


Usually forms for the inside of parapet walls are made 
in panels erected as a unit. Panels 10 to 12 ft. long are 
convenient for the average job. To support the back form 
until the roof slab concrete is placed, two 1x4 pieces for 
each panel are nailed to the studs and rest on the roof 
slab form as shown in Fig. 82. These supports are pointed 
to facilitate removal, which is done before the concrete 
hardens. Double-headed nails are used to fasten the 1x4 
pieces to the studs. 

A raggle must be provided to receive the roof flashing. 
There are numerous patented strips on the market that 
can be nailed to the inside of the form to remain in place 
when the forms are stripped, or the raggle can be formed 
with two triangular strips of wood. Nails are driven into 
the lower strip to extend into the concrete for anchorage. 
This strip remains in the concrete after the forms are re- 
moved. The upper and lower strips are both secured to 
the forms by means of double-headed nails. These nails 
are pulled before the form sheathing is removed, leaving 
both strips in the concrete temporarily. After the top 
strip has dried sufficiently to shrink it slightly, it can be 
removed without danger of spalling the concrete. 


SECTION 12 


patching plaster or similar material. Fig. 83 shows a care- 
fully erected form in which the joints have been filled 
with patching plaster wherever needed. Any surplus plas- 
ter is cleaned off with sandpaper. 

At some places it is difficult to draw the form tight 
simply with tierods, wales and braces. Liberal use of 
wooden wedges driven between blocking and sheathing 
will often serve to hold joints tight. Fig. 84 is a good 
illustration of the use of wedges. The corner is well tied 
and braced and any small amount of play between sheath- 
ing and blocking is taken up with wedges. Note that 
double-headed nails are used to make stripping easier. 

Studs, wales and ties must be placed close enough to 
prevent bulging of forms. It is better to make the mistake 
of spacing supporting elements of the form too closely 
rather than too far apart. A well-tied form for a fluted 
pier is shown in Fig. 86. The run moldings for the flutes 


Fig. 83 


are applied to a solid backing and the whole is erected 
as a panel. The ties are spaced on about 12x18-in. centers, 
which is probably closer than the concrete placing-rate 
required, but the holes left by the pencil rods are so small 
that they will not be noticeable when plugged. 

Inner and outer wall forms must be carefully aligned 
before the ties are tightened. If this is not done, the truss- 
like action of the walls acting together will make it very 
difficult to align the forms accurately. A method of align- 
ing wall forms was described in Section 11. 


Fig. 84 


Boxes, waste and wood 
molds, panels or anything S229 733.7 
appliedtothemainwallforms #4299°5e¢ in 
should be as lightly nailed as before temnov-|/ 
possiblesothatsuch partswill '"9 r™s 
pull loose from the forms 
when stripping and will re- 
main in the concrete. After 
the lumber has dried and 
shrunk, the ornamental de- 
tail forms can be removed 
easily without damaging the 
concrete. 

It is well to use double- 
headed nails driven from the 
outside of the forms wherever possible, because they can 
be pulled easily, leaving embedded parts of the forms in 
the concrete temporarily. When applying rustication 
strips to the face-side of a form such as shown in Fig. 83, 
however, it is advisable to use long casing nails as shown 
in Fig. 85. These should extend through the strip and 
through the form sheathing. Since the heads of these 
nails are very small the nails can be pulled through the 
strip and sheathing just before removing the forms thus 
allowing the wood strip to re- 
main in place until aitidis 
thoroughly dry. 

It is generally advisable, 
wherever possible (see page 19), 
to erect the outside forms first. 
If a form lining is used, a better 
job of applying it can be done. 
Waste molds can be more ac- 
curately set. Tie holes can be 
drilled from the face-side of the 
form thus avoiding burrs and 
allowing any pointing to be done 
more easily. The completely 
erected outside form can be in- 
spected and any joints or other 
places where leakage might oc- 
cur can be corrected. It is also 
simpler and more economical to 
place reinforcing steel. 

Construction joints should 
be placed, as previously men- 
tioned, where they will be 
least conspicuous, but it is 


Form.» 
“ sheathing 


Saw cut 


Fig. 86 


47 


/ Ny 


See 


/ } ; 
f ALi'strip /-——— Place concrete to 


’) PAN Allow to settle and pees 
Set ————- 4 strike off to bottom : 
TW ig \ of strip. Strip to be 


removed after 
concrete is hard, 
before stripping 


ts N 
5 1 
V forms. 
y Semi % Threaded bolt 
y NN 
J 
(je 


greased for easy 
removal. Bolt to 
V2" 4 hold forms for wall 
‘| above joint tight 
N against hardened 


v concrete 
gx | |_| 
ES, ; 


c= ees 412 ae SU As 


First STAGE 


sometimes necessary to locate them in flat wall surfaces 
where there are no architectural details to obscure them. 
By taking proper precautions, joints in such exposed 
locations need not be prominent enough to be objection- 
able. It is essential that there be no offset at the joint and 
no leakage. To do this, a %-in. stud bolt located not more 
than 4 in. below the joint should be provided to hold the 
forms above tightly against the hardened concrete as 
shown in Fig. 87. Unless the hardened concrete is at 
least four days old, a plate washer should be provided 
in addition to the nut to prevent breaking through the 
concrete. When the forms above the joint are stripped, 
the previously greased bolt is removed from the concrete. 
Wedges driven between the wale and the sheathing will 
help tighten the joint. A row of ties should always be 
located just above the joint to resist the pressure of the 
concrete. Dependence should not be placed upon bolts 
below the joint for this purpose. 

A straight construction joint is less noticeable than an 
irregular one. To produce a straight joint, tack a 1x2 
strip, as shown, to the lower form and bring the concrete 
just slightly above the bottom of the strip. If any laitance 
comes to the top of the concrete, it can be cut off with 
a trowel. The strip is removed after the concrete has set 
enough to hold its position. When the next lift of con- 
crete is placed, there will be a straight true joint. 


Oiling and Wetting 


Board forms should be soaked with water at least 12 
hours before concrete is placed. This tends to tighten 
joints, prevents absorption of water from the concrete 
and facilitates stripping. If the forms are badly dried out, 


48 


y /) 
PSS V 
level of broken line. Gey) wait 


Tie rod not 
over G"above 


Fig. 87 


Lap over hardened 
concrete not more 
than |" 


%' Threaded bolt 
greased for easy 
removal 


SECOND STAGE 


soaking with water at least twice daily for three days 
prior to placing concrete may be necessary. 

Plywood and fiberboard forms must be oiled, lacquered 
or given a special form treatment. If oil is used, an excess 
of oil must be avoided as it may stain the concrete. It is 
desirable to prepare the plywood on the ground because 
it can be done more thoroughly. A wide brush is suitable 
for the purpose (see Fig. 88) or the sheets of plywood 
may be dipped. All surplus form treatment is removed 
with waste or is allowed to drain off by standing the ply- 
wood on edge. Plywood treated at the mill will require 
less oil, lacquer or other treatment on the job and more 
reuses will be obtained. Linseed oil cut with kerosene is 
good for oiling plywood, but any of the other materials 
made specifically for the purpose is satisfactory. Metal 
molds must be thoroughly cleaned of all rust before oil- 
ing with a very light oil. 

Fiberboard should be greased with grease having a 
calcium stearate soap or aluminum stearate base, or 
should be oiled with a paraffin base oil having a viscosity 
of not less than 250 seconds at 100 deg. F. free from 
volatile constituents. 

Waste molds should be thoroughly dry before being 
given two coats of shellac. The molds should be shel- 


lacked before leaving the shop. After being set in the 
forms, joints filled and all patching done, the new plaster 
should be touched up with shellac. The molds must be 
greased with a light yellow cup-grease, which may be cut 
with kerosene if too thick. The grease should be wiped 
into all angles of the mold and every bit of surplus grease 
carefully wiped off. Care must be taken not to drop oil, 
grease or shellac onto hardened concrete or reinforcing. 


Stripping 


Careless workmen can nullify the value of good detail- 
ing and planning by indiscriminate use of pinch bar and 
sledge. It is worthwhile to impress upon workmen that 
corners must not be broken nor surfaces damaged and 
that maximum reuse of material is desired. A little time 
spent in training the stripping gang in the order and man- 
ner of removing forms will result in a better and more 
economical job. 

A pinch bar or other metal tool should never be placed 
against the concrete to wedge forms loose. If it is neces- 
sary to wedge between the concrete and the forms, only 
wooden wedges should be used. 

As arule, no forms should be stripped in less than four 
days after the concrete is placed. Ties may be removed as 
early as 24 hours but the forms should remain in place. 

When stripping forms in the vicinity of a belt course, 
cornice or other projecting ornament, begin stripping 
some distance away from the ornament and work toward 
it. In this way, if there is any tendency for the forms to 
bind around the ornament the pressure of the forms 
against projecting corners will be relieved so there will 
be less chance of spalling sharp edges. 

Forms recessed into the concrete require special care 
_ in stripping. To remove rustication strips, for example, 
start at a corner, window opening, or some place where 
it is possible to get a wooden wedge behind the strips. 
The wedging should be done gradually and should be 
accompanied by light tapping on the strip to crack it 
loose from the concrete. Never remove a rustication strip 
or other embedded form with a single jerk after it has 
been started at one end. Such forms should always be 
left in place as long as possible so they will shrink away 
from the concrete. Fig. 89 shows the result of careful 
workmanship in forming rustication. Note some strips 


Fig. 89 


Fig. 90 


still in place. Where both ends of a form are tight against 
offsets in the concrete, if the form is made in at least two 
parts with the joining made on a 45 deg. miter, stripping 
will be easier. 

The stripping of waste molds should be entrusted to a 
man who is familiar with the detail. While proper greas- 
ing of the mold will facilitate stripping, the plaster will 
usually stick to the concrete, at least in the undercuts. 
This must be cut away with a cold chisel and the work 
must be done carefully. Waste mold should be left in 
place (see Fig. 90) until all adjacent forms are stripped 
and until there is no danger of damaging the ornament 
due to other work in the vicinity. The mold also holds 
the moisture in the concrete, affording good curing. 

After forms are stripped, all material must be thor- 
oughly cleaned of hardened concrete. Some concrete will 
always adhere to sheathing lumber in spite of thorough 
oiling or other treatment. A tool made to fit the tongue 
and groove of matched boards will save time in removing 
concrete from the edges of boards. 

All nails should be pulled from sheathing boards, ply- 
wood and fiberboard. Never bend nails over by hammer- 
ing them against the face of the material. Holes which 
were bored through sheathing for form ties may be plug- 
ged by driving in common corks and cutting them off 


49 


flush with a sharp chisel or fine saw. Patching plaster can 
also be used for this purpose. 

Parts of boards that are split, or from which the tongue 
and groove have been broken, should be culled to avoid 


ESTIMATING 


DISCUSSION of the entire subject of cost estimating 1s 
beyond the scope of this publication; only the gen- 
eral principles of estimating form costs will be considered. 


Labor 


The labor cost of fabricating, erecting and stripping 
forms is usually estimated on the basis of square feet of 
contact area. It is customary on a job with a normal 
amount of ornamentation to take off the total contact 
area as though the wall were plain. Window and other 
openings, unless very large, are figured solid. The area 
thus obtained is priced as though the wall were unorna- 
mented; the area of the openings figured solid will offset 
the greater amount of labor required to form them. 
Separate allowance is made for ornamental details as 
explained later. 

For plain walls with an average amount of breaks and 
reveals, the labor cost for ordinary lumber forms for the 
exposed surfaces may be based on a carpenter erecting 
80 to 100 sq.ft. of forms in an 8-hour day. In addition, 
about 4 hours of laborers’ time will be required. About 
10 per cent more inside forms than outside forms can be 
constructed in the same length of time. 

Plywood applied directly to the studs will cost slightly 
less for labor than 1x6 T and G boards, the difference 
being 5 to 10 per cent, depending upon whether the wall 
is composed of large flat surfaces or is cut up considerably. 

Thin plywood or fiberboard applied over tight backing 
will cost slightly more for labor than ordinary wood 
forms. A carpenter can apply about 40 to 50 sq.ft. of 
lining in an hour. 

A careful study must be made of each ornamental de- 
tail to determine the additional number of hours of labor 
necessary to cut and fit the forms, set molds in place, 
provide extra backing and bracing, and to patch and 
point waste molds. An allowance must also be made for 
extra labor required for stripping waste molds, especially 
if there are many undercuts. These allowances for extra 
labor are generally added as a lump sum for each detail 
considered separately. Only through experience can these 
costs be established, because they depend upon the ability 


30 


loss of time in erection. Cleaned lumber should be sorted 
by size and length and stored in neat piles. Plywood and 
fiberboard should be laid flat out of the sun to keep edges 
from curling. 


SECTION 13 


of the workmen and the foreman and upon the com- 
plexity and size of the detail. It is therefore important on 
each job that cost records be kept of the formwork for 
every ornamental detail, until sufficient data are accumu- 
lated on which to base future estimates. 

The cost of labor for cleaning and treating forms is 
sometimes included in the square-foot price of erecting 
and stripping. It is better, however, to keep such costs 
separate both when estimating and when keeping cost 
records. A laborer should clean hardened concrete from 
lumber, remove nails and treat the material for reuse at 
the rate of about 100 sq.ft. of forms in 2 hours. 


Material 


Until sufficient experience is gained to estimate quite 
accurately the quantity of form material required by in- 
spection of the architect’s drawings and the contractor’s 
key drawings, it is advisable to take off an accurate bill 
of material. All boards and dimension lumber should be 
listed according to sizes and lengths required for the vari- 
ous locations. A summary sheet can then be made, group- 
ing the material of the same size into commercial lengths. 
Due allowance should be made for reuse of material as 
well as for waste. The latter will amount to about 10 per 
cent each time the material is reused. The waste on 
sheathing will be somewhat higher and on dimension 
material, appreciably less. 

For rough estimating purposes, it can be assumed that 
3 to 34% board feet of lumber will be required for each 
contact foot of forms for one use; if no material were 
wasted and three reuses were contemplated, the total 
amount of material indicated as necessary for the entire 
job should be divided by 3 to ascertain the quantity to 
buy. High walls and a rapid rate of placing the concrete 
will increase the quantity of material for each contact 
foot, due to closer spacing of studs and wales. 

The cost of ties will depend upon the type used. If 
pencil rods are used, the only material consumed is the 
rods and a few buttons which may be lost. A charge of 
one cent a square foot of wall area will usually be ample 
for ties, nails and bolts. 


Fig. 91—Los Angeles County Medical 
Association Library, Los Angeles. 
Gordon B. Kaufmann, architect ; Wm. 
Simpson Construction Co., contractor. 


A TYPICAL JOB 


HE fundamentals of design and construction of forms 
for architectural concrete work have been discussed 
and illustrated in the preceding sections. Of necessity, 
many principles, methods and details have been consid- 
ered more or less independently of the other factors, all 
of which should be taken into account on each specific 
job. As a summary, therefore, in this chapter, the forms 
for a typical small building will be analyzed. 

For the sake of brevity, only one elevation will be con- 
sidered in detail. A picture of the completed building is 
shown in Fig. 91. The design is relatively simple, yet 
practically all types of forms or kinds of material dis- 
cussed in this booklet either are required in the construc- 
tion or might have been used in alternative methods of 
forming the job. The method chosen for the purpose of 
illustration may not be the one used by the contractor, 
but it is a practical method which would produce good 
results economically. 


SECTION 14 


Planning the Job 


It will be assumed that the building has a volume of 
approximately 160,000 cu.ft.; total contact area of forms 
including floors, roof and walls above grade is roughly 
30,000 sq.ft. and the area of the front elevation is about 
1,660 sq.ft.; for the purpose of this example, the total 
quantity of concrete will be taken as 700 cu.yd. 


Speed of Erection and Type of Forms 


The approximate time required for completion of the 
concrete work and the size of crew required to do the 
work are estimated in accordance with the rules given in 
Section V. 

Assuming that panel forms can be used, except for the 
front elevation which does not lend itself to forming with 
panels because of the ornamental detail, approximately 


-_ 


oa | 


16 carpenters and 8 helpers will fabricate, erect and strip 
the forms for the entire building above grade in about 
three weeks. Allowance for building the front wall forms 
in place and for the ornamental detail will add roughly 
three days to the required time for forming. 

Setting of reinforcing will proceed during the erection 
of forms and will not appreciably add to the duration of 
the job. 

Using a 4-yd. mixer and a crew of 25 laborers, roughly 
six days will be required to place the con- 
crete. 


Time Forms Must Remair. in 


forms will be in panels small enough to be handled by 
hand or with a hand-operated “A’’-frame hoist. The job 
is too small to warrant power equipment for form 
erection. 


Order of Stripping 


In general, the order of stripping will be the reverse of 


—-A | 


| — 


Construction joint kaa 


LTT 


Place—Reuse of Forms 


To avoid delay while waiting for forms to 
be stripped, sufficient material will be pro- 


» [E LOS ANGELES 


AL ASSOGIATION | 
Construction joint "B’>\ _ 


vided to form the entire building up to the 


construction joint B at the belt course just 
beneath the building name shown in Fig. 


92. One reuse of a part of the form lumber 


will thus be obtained. Some allowance may 


be made for using most of the wales from 


the first story in the story above before the 
balance of the first-story form material has 
been removed. 


Construction Joints 


Two of the three joints in the front eleva- 


Construction joint “A” 
at floor level : 


tion are located where they are concealed 
by architectural details. The lowest joint is 
at the floor-level and follows the outline of 
the pediment over the doorway and the 
niches at each side. It is convenient to lo- 
cate the joint at the top of the floor slab, 
but it would be slightly less noticeable if 
raised to the level of the top of the niches. 
With horizontal joints located as shown, 
vertical stoppings dividing the building in- 
to two parts will be needed to keep the 
quantity of concrete to be placed in a day 
within capacity of the plant and crew. 


Order of Erection 


The building is the type described under Plan 1 (page 
20) and the order of erection suggested there will be fol- 
lowed, namely: 

1. Erect outside wall forms and bring to alignment. 

2. Erect inside wall forms and floor forms. 

3. Check alignment, tighten braces and bolts. 


Erection Methods 


The front wall forms will be built in place and other 


52 


[G" Mee TG 
MG T Dei 
PART PLAN OF WEstT Facade 


Fig. 92 


the order of erecting the various parts of the forms. This 
subject will be considered more fully in the discussion of 
the form details. 


Detailing 


Figs. 93 and 94 are typical of the key drawings neces- 
sary to show the form details for this job. Additional 
details or sections would be required to show the forms 


Cw, WW fies) 
| Ne 
\! 
1 


I ~ 
| Sey 
i 1 iI 
| ib \! 
| 
. | \! 
Construction Nea i! 
joint cow | | i! 
sxe moe | i! 
“as re 
3 ' kao 
on ae | 
Construction | 
joint *B’———1 ll 
Plaster Seth Ul 
se ml waste 
hay molds 
ae + 
t— %"?Holes 
lo"o.c. 


surface, so plywood is adopted as form sheath- 

ing. Eleven-sixteenth-inch plywood is applied 

\ directly to the studs. Ordinary boards or ply- 
ee wood may be used for the inside forms with- 
out material difference in cost. Twenty-four- 
inch-wide sheets produce a jointing in keeping 
with the proportions of the building and are 
slightly cheaper than wider sheets, so 24x48- 
in. or longer sheets will be used for the job. 
Either plaster or wood letters will be satis- 
factory. The choice will depend entirely upon 


price. The belt course and cornice are shown 
formed with plaster molds because the amount 


22 al) | Construction 
A. Joint “B" 


Lt 


* Pa 
— 2x 4" Studs 


of repetition will undoubtedly make waste 
ix molds more economical than wood. Plaster 
3inall molds have been used for the columns at the 
i entrance and for the niches, although it is 
« possible that wood molds for the fluting in the 
niches would be more economical. For such 
details it is often desirable to get mill and 
waste moldmaker’s prices before making a 
final decision. The fluting at the sides of the 


Studs 2x4°54S. Plaster 


entrance can best be formed with wood molds 


waste 
mold 


spaced |0"o.c. 


Wales 2x 4"S4S. 
spaced 24"o.c. 


Ties ¥' round 


as shown. 

The height between construction joints is 
less than 12-ft. and so a 2-ft. an hour placing- 
rate would be adequate to complete a section 


Construction 
joint “A” 


Construction 
joint “A” 


Fig. 93 


for steps, flower area curbs beneath niches and for other 
incidental details. To illustrate the tying and bracing of 
the forms, the studs, wales and ties are shown, which is 
not customary on contractor’s key drawings. Likewise, 
to avoid confusion in the small scale drawings, dimen- 
sions of details which should be shown on job drawings 
have been omitted. 

The architect’s design calls for a relatively smooth wall 


LS Sie Ye ios us 
SECTION 2-2 


from joint to joint in six hours. At the assumed 
placing rate of 2 ft. an hour it is known from 
the design examples presented on pages 6 to 
9 that stud spacing must not exceed 16 in. 
and assuming 2x4 studs S4S the wales should 
be 24 in. apart and tie spacing will be 27 in. if 
double 2x4 wales S4S are used. Ifa faster plac- 
ing rate must be used on some portion of the 
job, the forms should be designed to resist the 
corresponding pressure. 

Note in Section 1-1, Fig. 93, that the out- 
side forms at construction joint A lap over the 
hardened concrete and are secured by a bolt 
embedded in the concrete. At the other two 
joints this is not necessary because there is an 
offset in the architectural design at those places. 

The offsets and deep reveals in the elevation 
and the batter on the wall complicate the form- 
ing slightly, although no serious difficulties 
are encountered. Because of the width of the offsets near 
the roof line, the studs should be lapped as shown to in- 
sure ample rigidity. 

The provision made for holding corners and angles of 
forms tight should be carefully studied. Ample ties, tight 
joints and solidly blocked corners are of utmost impor- 
tance. The wood molds for the fluting are shown applied 
to a solid backing which will hold the joints tight and 


(23) 


93 


as G. sheathing 


Window box built at bench 
cee: + 


. bay 
Kick block— 


Blocking 
between 


Se 


| 2-2 4"Wales—~ | 


=e 


>= I"Blocking 2!0"0.c. 
2x64 


__|—Plywood sheathing 


| + — "Ribs 16"o.c. 


| — |"x 4"Sheathing covered 
with 4 plywood 


At r 
Panel raised from Ist.story 
HORIZONTAL SECTION SHOWING WINDOW FORM 


Plywood sheathing 


2 


+ 


1 
' 
' 


Fluted forms made up as panel 
erect and strip as unit. 


58 Plywood for all 
exterior surfaces 


Al A PR 
=— 2-2'x 4" Wales 


‘ 
' 
1 


+ 


Plaster waste Sell 


ca 


as 


HORIZONTAL SECTION THROUGH WEST FACADE 


Fig. 94 


that part of the forms can be moved up as a panel. Note 
the joint between the panel and the adjoining form is 
made at a stud. 

The forms for this job are very easy to strip. Tierods 
are first loosened. At the same time, kick-strips holding 
the intersections of the wales are knocked off. The wales 
may then be removed. Next the studs should be removed 


34 


from the sheathing, except where the wood molds for the 
fluting are to be moved as a panel. As the studs are pried 
up, beginning at the bottom, the plywood sheets will be 
loosened from the concrete and can be removed without 
damage if the sheathing has been lightly nailed to the 
studs. The waste molds should be removed last and only 
after all work in the vicinity has been completed. 


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CONDUITS 


Ss CONCRETE 
mm 6CULVERTS 
= AND 


CONCRETE CULVERTS 


and CONDUITS 


The activities of the Portland Cement Association, a 
national organization, are limited to scientific research, 
the development of new or improved products and 
methods, technical service, promotion and educational 
effort (including safety work), and are primarily de- 
signed to improve and extend the uses of portland cement 
and concrete. 

The manifold program of the Association and its varied 
services to cement users are made possible by the finan- 
cial support of over 70 member companies in the United 
States and Canada, engaged in the manufacture and sale 
of a very large proportion of all portland cement used in 
these two countries. A current list of member companies 
will be furnished on request. 


Published by 


PORTLAND CEMENT ASSOCIATION 


33 West Grand Ave., Chicago 10, Il. 


A STUDY IN CONTRASTS 


—dilapidated highway bridge 
and typical replacement struc- 
ture, Tarrant County, Texas. 


TABLE OF CONTENTS 


Section Subject Page 
INTRODUCTION Ge fark oe ee es ee Pb es RO a Oe ees 
I—GENERAL CONSIDERATIONS FOR DESIGN... .. . . . .. . 6 
Use of Culverts 
Determination of Culvert Capacities . . . . .. ..... . . 6 
Capacities as Affected by Culvert Characteristics . . . . . . .. . 10 
Determination of Run-off by Other Methods . ..... .. . .I11 
Culvert) Locationvame as ieee tae oe 3 ok fe See eee 
Alignment@ eee ee ee ee EE! ee sO a ee |S, 
Slopes ae eee eee a Se Se ee eee | 2 
Eleva tioreammete es | oe Ura MS a et ee ee, ~ eee 2 
Culvert; Losdsmipae ares t get be fo ccs en ke Ok) ee ee eee 
Live; Loads ream. eee ene eee cs es 0 0 A. 1) ee 
Wheel Loads on Exposed Slabs... . . . . . . ~. +. +. +. *1 
Wheel Loads on Covered Slabs . . . . . . . . =. ~~. ~..:~S«ts&d‘ 
Deadsloadsmart amr. 2. eed one) se Tee fb A, =? Be, oe 
Special Requirements in Construction of Large Culverts . . .. 16 
Verticalglioad es (4,0) ht) hoe SE” rel 
ateralsPressuress): ee) 4.5 oe Re LS 
Ghoicezof-Culvert Shape > 2... tes «© 5 « +» 5 & = w @ = on20 
Boxa@ulvertsm emer ie ew ane alge Os Joe 2 SO) 
Modified Circular Culverts and Conduits. . . . . . . . . . . 20 
Design Loads and Procedures .......... . . . . . 22 
ORCS MEER MED rete fos eh. 3s (Oe §S hea et © pee GE ee eee 
DesignsConsiderations «9. «93 «2: «© © © «© » «© «= 9) = == G24 
Construction#yointsA-.5, 3 & . 2° A ph ee Ga ee eee ee ee 
Expansion and Contraction Joints. . . ........ . . 25 
Unit Stresses Suggested for Design. . . . . . . .. . . . ~. 26 
Method of Designing Sections . ...... . . . . . . . 26 
iy picalsDesigns meme wr cen Ee 3 es Se ee, oe ye a) roo 
II—ANALYSIS AND DESIGN OF SECTIONS. ........ . . +. +. 30 
Square: One-Cell Culverts. 0. 6 i) ae EE ee 80 
Rectangular One-Cell Culverts . . . . . . . . . . . . . . . 33 
wo=-CelléBboxtCulverts -. (5 9 6) is hn 35 
wehree-GellsBoxeGulverts? 4. 20°). oe oe Os ee Be edo 
Modified Circular Culverts and Conduits. . . . . .. .. . . . 40 
Type I Culverts or Conduits. . . ....... . . . . = . 40 
Type II Culverts or Conduits . ......... . . . . 46 
Head Walls, Wing Walls and Cutoffs. . . . . .. . . . . . . 50 


The drawings in this publication are typical designs and should not be used as working drawings. 
They are intended to be helpful in the preparation of complete plans which should be adapted 
to local conditions and should conform with legal requirements. Working drawings should be 
prepared and approved by a qualified engineer or architect. 


FOREWORD 


In this booklet culverts and conduits are discussed from the viewpoint 


of the engineer who must design them. The treatment of fundamental 
considerations is brief and leads to practical methods by which economical 
drainage structures may be chosen, properly located and correctly designed. 
Sections on design of structures illustrate procedures which permit short- 
cut design without extended analysis. 

The necessity for economical, safe construction is apparent. Generally, 
the states demand the same engineering attention to culvert design as is 
given to other more impressive structures in the highway system. 

Culvert design requires time and thought. As a guide for designing 
culverts and to aid you in checking designs made to meet specific local 
conditions, illustrative examples are included and typical designs have 


been prepared and presented here for a wide range of field conditions. 


Altractive box culvert on 
Natchez Trace, Miss. Excel- 
lent inlet conditions were 
obtained by paving the 
transition with precast con- 
crete riprap and molding 
the edges of the culvert to 
smooth curves. 


CONCRETE CULVERTS 
and CONDUITS 


INTRODUCTION 


4a factors are responsible for the costly replace- 
ment of many drainage structures early in their 
anticipated useful lives. First, and foremost, is the 
destruction wrought by storm floods to inadequate 
bridges and culverts. One who has attempted to use 
highways in a flooded area can appreciate the extent 
of such damage. Second, and much less apparent, is 
the progressive damage to highway structures caused 
by heavy trucks. 


Periodic floods have steadily grown in destructiveness. 
Extremely high rates of surface run-off result from 
gradual changes in the character of the country. The 
clearing of timber and underbrush for farms, followed 
years later by removal of the areas from cultivation, 
have transformed a much greater percentage of rainfall 
into run-off. Drainage structures of ample capacities in 
the past are less able now to handle excessive flows 
without washouts. 


Comparable with flood action is the gradual weaken- 
ing of inadequate bridges and culverts under modern 
transport. Limited appropriations and short term plan- 
ning often require costly maintenance of such struc- 
tures, year after year, while ever mounting traffic loads 
are to be carried. 


The New England floods of 1936 destroyed nearly 
700 small bridges and culverts, not a score of which 
were modern. This necessitated the building of new 
structures to modern and safe standards. The $13,000,000 
replacement cost was not considered a loss, for it 
represented an improvement that would normally have 
taken over 25 years to accomplish. 


Some far-sighted communities have not waited for 
floods to force needed improvements, but have inaugu- 
rated programs for systematic replacement of obsolete 
highway structures. Theaction taken by Tarrant County, 
Texas, is typical of what can be done*. In 1936 this 
county had over a thousand antiquated bridges and 
culverts on its 1400-mile system. $50,000 a year was 
required to keep these structures in passable condition. 


Current funds were not sufficient for modernization, 
but a $400,000 bond issue, the county’s share of the 
cost of replacement, was floated at a yearly cost to the 
county materially less than the $50,000 maintenance 
cost. In 1939, the county proceeded, with Federal 
assistance, to replace its dilapidated, obsolete bridges. 
A total of 1,438 bridges were built. As anticipated, 
the savings in maintenance paid the county’s share 
of the construction cost in 10 years and the useful 
life of the structures has only started. 

Other counties can replace their obsolete drainage 
structures economically and efficiently as did Tarrant 
County. Standardized methods of reinforced concrete 
design for culverts and small bridges have become effi- 
cient tools in the hands of the county engineer, allowing 
him to make economic use of that durable construction 
material. Attractive, low-maintenance-cost structures 
may be designed for any combination of site conditions. 
Special requirements are incorporated in a structure 
without sacrificing such qualities as rigidity and strength 
against overloads; weight and stability against flood 
flow; resistance to chemical attack by harmful materials 
in foundations; and ability to meet other unforeseen 
conditions. 


The purpose of this booklet is to present brief, prac- 
tical suggestions on types of reinforced concrete highway 
structures best suited for different purposes. Thorough 
consideration is given to basic elements of design. 
Typical designs are presented covering a wide range to 
meet most local conditions. The booklet is divided into 
two divisions covering: 

General considerations on design of culverts and con- 

duits. 

Specific designs of different types of culverts and 

conduits. 

*Described in detail in Concrete Highways and Public Improve- 


ments, November-December, 1939, published by the Portland 
Cement Association. 


One of the box cul- 
verts resulting from 
the modernization 
program in Tarrant 
County, Texas. 


SECTION I—GENERAL CONSIDERATIONS FOR DESIGN 


A culvert may be defined as a transverse drain or 
waterway under a road, railroad, canal, or channel. By 
ordinary engineering usage, however, culverts refer only 
to short structures through roadway or railroad embank- 
ments, serving as passageways for water and normally 
not acting under hydrostatic head. Structures under 
canals or natural channels and having a “‘sag”’ or definite 
drop and rise in grade between inlet and outlet are 
known as inverted siphons. Long drainage structures, 
usually buried but not necessarily under embankments, 
in which hydraulic considerations are important come 
under the general classification of conduits. Included 
are storm drains, sewers, and pressure pipe lines. 


This section refers particularly to culverts as ordi- 
narily defined and less directly to conduits. It should 
be noted, however, that the most difficult problems 
encountered in the design of conduits are considered 
and useful data are presented. Emphasis has been placed 
on the determination of earth pressures and the design 
of sections for both types of structures. The designer 
is given the choice of several different shapes and can 
proceed rapidly through his design by use of tabulated 
coefficients. Suggested designs based on average condi- 
tions are also presented for the aid of engineers. 


Use of Culverts 


Before the development of the multi-celled culvert 
there was a definite dividing line between conditions 
calling for culverts and those requiring small bridges. 
The latter were used to span openings of considerable 


6 


size or importance while culverts were relegated to 
minor openings. This distinction no longer applies arbi- 
trarily as it is recognized that the efficiency and low 
cost of culverts make them desirable for a wide range 
of conditions. 

The need for a long, single span is the main deterrent 
against selection of a culvert for some locations. This 
is important for wide crossings where stream bed con- 
ditions are unfavorable for culvert floor slabs or division 
walls. Furthermore, long spans obstruct the passage of 
debris during flood stages far less than do culvert open- 
ings. This factor may eliminate culverts in timbered or 
drift-littered watersheds. The possibility of ice jamming 
culvert inlets in cold regions should also be considered. 

Where the above factors do not control, culverts are 
excellently adapted. Culverts have a low maintenance 
cost, may be cheaply lengthened when a wider roadway 
is necessary and do not limit visibility on curves. 


From a structural standpoint, culverts are advan- 
tageous because of their continuity. Unexpected loads 
or other unusual conditions are better resisted by cul- 
verts as all component parts contribute helpful restraint 


Determination of Culvert Capacities 


The first consideration in culvert design—and one of 
the most important—is the determination of required 
capacity. In general, the estimated volume of water to 
be carried by a culvert is based on the probable maximum 
run-off to be reasonably expected at the site. This need 


Concrete arch culvert built in 1928 over Ritchy Run near 
Clarion, Pa. The barrel has a span of 24 ft. at the base 
and a clear height of 18 ft. 


not be guesswork, as pertinent data can be obtained 
by one or all of the following procedures. The accumu- 
lated information will aid the engineer’s judgment in 
arriving at the required culvert size. The refinement to 
which each study should be carried depends on the 
importance of the culvert. 


1. Inspect the culvert to be replaced or the site for 
evidences of the magnitude of past flood flows. 
Other structures on the same watershed may also 
give clues to the volume of run-off that may occur. 


2. Study local records or statements made by resi- 
dents to learn intensities and durations of heavy 
rainfall in preceding years. Reference should be 
made to U.S. weather reports and rainfall or 
drainage tables. 


3. Examine watershed to learn the topography, char- 
acter of surface cover, slope or ‘‘lay of the land” 
and type of soil. Large areas usually cause heavy 
run-off, but the other characteristics of the water- 
shed are important. Thick vegetation or timber 
reduce or retard run-off as do highly absorptive 
soils. Reliance should not be placed upon helpful 
effects of surface cover, however, when there is a 
definite possibility that at a later date the area 
will be denuded and allowed to become meadow 
or wasteland. There have been many instances of 
cleared tracts where rainfall has produced nearly 
100 per cent run-off. 


4. For large, important drainage structures it is advis- 
able to survey the water course. Then, having 
determined the average slope of the stream bed 
and the cross-sectional area up to high water stage, 
the volume of flood flow may be computed by 
hydraulic principles. The common way of doing 


this is by use of the Chezy Formula: 
Q = CAV rs 
in which: Q = discharge in cubic feet per second 
A = cross-sectional area of drainage channel 
up to high water level, in square feet 
r = hydraulic radius (A divided by the wet- 
ted perimeter of cross section, in feet) 
s = slope (change in elevation, in feet, divided 
by length considered, in feet) 
C = coefficient of roughness of channel 
Values of C for different types of drainage channels 
are given in textbooks on hydraulics. For approximate 
computation the following classifications are helpful: 
C varies from 60 to 80, for clean earth channels 
C varies from 45 to 60, for stony earth channels 
C varies from 35 to 45, for rough rocky channels 
C varies from 30 to 35, for badly obstructed channels 


A more accurate value of C may be computed from 
Kutter’s Formula: 


1.811 
rage + 41.6 + 


C= 
0.00281 n 
(aap SED) 
i Ss Vr 


in which r and s are as in the Chezy Formula, and nis a 
coefficient which depends only on the roughness of the 
channel. n has values from 0.020, for clean, smooth 
channels, to 0.060, for exceptional cases of badly 
obstructed channels having heavy vegetation. An 
average value. of n is 0.035. This applies to partially 
obstructed channels. 


0.00281 
S 


Equivalent waterway area = 255 + 6x5 + 1545 = 90 sq. ft. 


2 
Wetted perimeter = 10.3+G+ 15.8 = 32.1] ft. 


Hydraulic radius =22 = 2.8 ft. 


Fig. 1. Channel cross section. 


Example: Assume that the flood flow of a small drain- 
age channel is to be estimated, and that there are visible 
evidences of the height to which past maximum flows 
have risen. Fig. 1 represents a measured cross section 
taken at a point where the channel is relatively straight 
for a distance of approximately 500 ft. up and down 
stream. Levels were run over this 1,000 ft. and the slope 
was found to be approximately 0.005 (0.5-ft. vertical 
drop per 100-ft. horizontal distance). 

The dashed lines in Fig. 1 are drawn to give an 
equivalent cross section from which area and wetted 
perimeter can be quickly computed. In this case the 


7 


cross section is taken as two triangles and a central 
rectangle. If the drainage channel is of the type for 
which C is approximately 45 (see classifications on 
page 7) then the flood discharge is: 


Q = CAV rs = 45 X 90 V2.8 X 0.005 = 480 cu.ft. 


per second. If n had been taken as 0.035, the computed 
value of C by Kutter’s Formula would have been 


0.811 0.00281 

0.035 + 41 + 9.005 
oe 0.00281\ 0.035 
1+ (416 == 0.005 om 


_ 51,74 + 41.6 + 0.56 
~ 1442.16 X 0.0209 


and Q = 50 X 90 V 2.8 X 0.005 = 530 cu.ft. per second. 


5. Use an empirical formula to estimate the waterway 
opening required. Note that empirical formulas for 
waterway opening do not take the place of other 
procedures for estimating run-off, but are only to 
be considered as supplementary. 

A good estimate can usually be made by the Talbot 
Formula* when all the factors that influence run-off 
are not exactly known. This formula takes into account 
the area of land draining into the culvert, the shape, 
the approximate slope, and an assumed rate of rainfall. 


Talbot Formula: A = CM” 
in which: A = waterway opening in ‘square feet 
M = area of watershed in acres 
C = a coefficient that depends on the slope 
and character of the watershed 


.C = ¥¢ for flat areas not affected by accumu- 
lated snow, where the length of the 
watershed is several times the width 


C = ¥ for rolling farm land where the length 
of the watershed is about three or 
four times the width 

C = 2 for rough, hilly watersheds having 
moderate slopes 


= 50 


C =1 for steep, barren areas having abrupt 
slopes 


The formula was originally intended for use in the 
Midwest and was based on a rainfall intensity of about 
4 in. per hour. By its use one can obtain satisfactory 
results in other parts of the country as well, by dividing 
the computed waterway opening by 4 and multiplying 
by the rainfall rate for the locality considered. 

Selection of a high rainfall rate results in larger culvert 
capacities because of the greater volume of run-off to be 
carried. Use of a high rainfall rate therefore will mean 
an additional factor of safety against possibility of 
washout or other damage to the highway, but care 
must be exercised to avoid wasteful oversize in an effort 
to insure adequate capacity. 

Maximum rates of run-off occur during or after severe 
rainstorms, which may be divided into two classes: 
(1) rains of great intensity and short duration, and 


8 


(2) rains of more moderate intensity and longer dura- 
tion. Intense, short rains are usually the more destruc- 
tive because of the high run-off resulting. Rainfall rates 
taken from records of such storms are therefore needed 
as a guide in estimating the intensity and frequency of 
future storms. For ordinary purposes, the summarized 
records and charts as presented in various technical 
bulletins are sufficient. One of the most exhaustive and 
pertinent of these is Rainfall Intensity—Frequency Data 
by David L. Yarnell, U. 8. Department of Agriculture, 
Miscellaneous Publication No. 204**. Diagrams in this 
publication give the probable maximum rainfall in any 
section of the United States for rains of different dura- 
tions. The expected intervals in years between any two 
of these intense rains is also given. 

The duration of a rain on any watershed affects the 
required culvert capacity, depending on the “time of 
concentration” for that watershed. The time of con- 
centration is the longest time required for rain fall- 


ing on any part of the watershed to reach the culvert 


as run-off. Usually this is the time required for run-off 
to reach the culvert from the most distant part of the 
watershed, involving an estimate which will be dis- 
cussed later. 

It is evident that maximum run-off through the cul- 
vert will occur when every part of the area is contri- 
buting, therefore a rainfall duration less than the time 
of concentration will not produce the greatest run-off 
at the culvert. 

To find the proper rainfall rate for use with the Talbot 
Formula, it is necessary to compute or assume the time 
of concentration for the watershed. Having the con- 
centration time, it is then necessary to ascertain the 
maximum rainfall rate, in inches per hour, for severe 
rains of that duration to be expected with reasonable 
frequency. An index to the severity of the rainfall is 
the number of years’ interval expected before another 
rain of equal or greater intensity. 

Accurate determination of time of concentration 
is frequently difficult but it is fortunate that rainfall- 
frequency data follow certain trends which may be 
utilized in preparation of diagrams. A rainfall rate of 
a certain severity applies to several types of rains, 
including those of short duration and short frequency, 
others of longer duration and longer frequency, and 
finally rains of long duration which might occur but 
rarely. Approximately the same relation holds for the 
entire country. For example, a 10-minute rainfall of 
high intensity occurring once in 10 years will have a 
maximum rate of rainfall approximately equal to that 
of a 15-minute rainfall occurring once in 25 years. 
Except for this relationship, a diagram would be neces- 
sary for each of several rainfall durations in combina- 
tion with each of several ‘‘expectancy intervals’’. 


*“TDetermination of Water-Way for Bridges and Culverts” 
by Prof. A. N. Talbot, Selected Papers of the Civil Engineers Club 
of the University of Illinois, 1887. 

**For sale by the Superintendent of Documents, Washington, 
D. C.; price 10 cents. 


Fig. 2. Equivalent rainfall rates in inches per hour for 
average design conditions. 


Figs. 2 and 3* permit the selection of rainfall rates 
for two general design conditions without exact knowl- 
edge of concentration time. Fig. 2 represents rainfall 
rates considered high enough for average design condi- 
tions. In terms of duration and expectancy the diagram 
gives equivalent rainfall rates, inches per hour, for any 
of the following: 


a 10-minute rainfall, of intensity expected to be 
equaled once in 2 years 


a 15-minute rainfall, of intensity expected to be 
equaled once in 5 years 


a 30-minute rainfall, of intensity expected to be 
equaled once in 25 years 


Rainfalls of 60 minutes or longer are less than the 
plotted equivalent rainfall rates in Fig. 2 for any in- 
terval of years. 


Fig. 3 represents unusually severe rainfalls, and is 
intended for use in design of drainage structures whose 
capacities must be adequate for very severe storms of 
rare occurrence. In terms of duration and expectancy of 
these storms, the diagram gives equivalent rainfall rates, 
inches per hour, for any of the following: 


a 10-minute rainfall, of intensity expected to be 
equaled once in 10 years 


a 15-minute rainfall, of intensity expected to be 
equaled once in 25 years 


Rainfalls of 30 minutes or longer are less than the 
plotted equivalent rainfall rates in Fig. 3 for any in- 
terval of years. 


A short discussion will illustrate why Figs. 2 and 3 
may be used with confidence in all but exceptional 
cases. 


Assume that average design conditions are satis- 
factory in a particular case, and that Fig. 2 is used for 
determination of culvert capacity. Since short intense 
rains have the greatest rates, rainfalls longer than those 
specified in the diagram will have less than the plotted 
rates. Likewise, if the time of concentration for the 
watershed is actually longer than anticipated, the 
plotted rates will give a greater culvert capacity than 


Fig. 3. Equivalent rainfall rates in inches per hour for 
unusual design conditions. 


needed, as the intense rains would be shorter than the 
actual period of concentration—a condition which does 
not produce maximum run-off for a watershed. 

Consider what might happen, however, if the time of 
concentration for the watershed were very short, say 
10 minutes. Rainfall rates from Fig. 2 might be exceeded 
by a 10-minute storm of greater intensity which would 
occur once in a period longer than 2 years. During such 
a storm the culvert capacity would be temporarily 
exceeded and the culvert would run under head. This 
would not be dangerous for the short time involved. In 
addition it should be remembered that times of con- 
centration short enough to force consideration of the 
more intense rainfalls of short duration could only 
apply to very small watersheds. A watershed of any 
appreciable size or importance would be entirely out 
of that category. 

Figs. 2 and 3, when used with Table I, facilitate the 
determination of culvert capacities for different parts 
of the United States. They are not sensitive enough, of 
course, for accurate use in small localities subject to 
rainstorms of highly variable nature. The striking dis- 


*Based on data given in Rainfall Intensity—Frequency Data. 
See reference, page 8. 


Four-span culvert bridge on Tennessee Highway 71 over 
Little Pigeon River, Gatlinburg, Tenn. 


similarity of rainfalls at such points will be apparent at 
once, however, in whatever local records are available. 
The possibility of ‘‘freak” storms is also not indicated 
in the figures. 

Table I is based on Talbot’s Formula modified to 
allow for variable rainfall rates. It gives values of 
CM% 
4 
values of C. See discussion on page 8. 


for different watershed acreages and different 


TABLE I. Waterway Areas (Sq.Ft.) Required to 
Drain Different Acreages, M, for Equivalent 
Rainfall Rate of 1 In. per Hour 


3 
4 
Values of a in sq.ft. 
M Flat areas not | Rolling farm | Rough, hilly | Steep, barren 
/ affected by | land. Length | watersheds | watersheds 
acres | accumulated | of watershed having having 
snow. Length | three or four| moderate abrupt 
several times | times the slopes slopes 
width width 
C= C= =% C=1 
2 0.08 0.14 0.28 0.42 
4 0.14 0.24. 0.47 0.71 
6 0.19 0.32 0.64 0.96 
8 0.24 0.40 0.79 119 
10 0.28 0.47 0.94 1.41 
15 0.38 0.63 eae Tet 
20 0.48 0.79 1.58 2.36 
29 0.56 0.93 1.86 2.80 
30 0.64 1.07 2.14 oral 
35 0.72 1.20 2.40 3.60 
40 0.80 1.33 2.65 3.98 
45 0.87 1.45 2.89 4.34 
50 0.94 1.57 3.14 4.70 
60 1.08 1.80 3.59 5.39 
70 121 2.02 4.03 6.05 
80 1.34 2.23 4.46 6.69 
90 1.46 2.43 4.87 7.31 
100 1.58 2.63 9.27 eH 
150 2.14 3.57 7.14 10.7 
200 2.66 4.43 8.87 13.3 
250 3.14 5.24 10.5 15.7 
300 3.60 6.00 12.0 18.0 
350 4.05 6.74 13.5 20.2 
400 4.47 7.45 14.9 22.4 
450 4.89 8.14 16.3 24.4 
500 5.29 8.80 17.6 26.4 
600 6.06 10.1 20.2 30.3 
700 6.81 11.3 22K 34.0 
800 7.52 LZ 29.1 37.6 
900 8.22 13.7 27.4 41.1 
1000 8.89 14.8 29.6 44.5 
1200 10.2 17.0 34.0 51.0 
1400 Its 19.1 38.1 57.2 
1600 12-7 211 42.2 63.3 
1800 13.8 23.0 46.0 69.1 
2000 15.0 24.9 49.8 74.8 
2500 Li@ 29.5 59.0 88.4 
3000 20.3 33.8 67.6 101.4 
3500 22.8 37.9 75.8 113.8 
4000 25.2 41.9 83.9 125.8 
4500 27.5 45.8 91.6 137.5 
5000 291 49.5 9-1 148.7 


Example: Approximate Determination of Water- 
way Opening Using Talbot Formula 


Assume, for illustration, that one must estimate the 
approximate waterway opening of a culvert in, say, 
northeastern Kansas. Based on average design condi- 
tions, for which Fig. 2 is prepared, the equivalent rain- 
fall rate is found to be about 4.6 in. per hour. The 


LIMITS _OF WATERSHED _____—-————___ 


Ss 


—— 


— 


ROADWAY 


= DRAINAGE CHANNEL 


i 
i] 
1 


CULVERT x 


drainage area of the culvert is as shown in Fig. 4, and 
comprises about 300 acres of rolling farm land. This 
description and the fact that the length of area is about 
three times the width, give a Talbot’s coefficient, C, 
equal to 4. 

In Table I, for M = 300 acres and C = 4: 

CM* 
4 

therefore, waterway opening = 4.6 X 6.00 = 27.6 sq.ft. 

It will be noted that the procedure just described 
gives waterway areas directly, with no consideration 
given to length or shape of culvert, type of inlet or out- 
let, slope of barrel and frictional resistance offered by 
the wetted surfaces of the culvert. Since capacities are 
most often based on roughly estimated volumes of 
water, it is not justifiable to introduce the effect of such 
variables in selecting the size of the average culvert. 
This does not mean, however, that the hydraulic prop- 
erties of the culvert are ignored. The smooth surfaces 
of concrete drainage structures, so desirable for hydraulic 
efficiency, insure the maximum discharge for a given 
waterway opening. This introduces a generous factor 
of safety in the capacity if run-off is closely estimated, 
and also provides extra capacity in the event run-off is 
underestimated. 


= 6.00 


Capacities as Affected by 
Culvert Characteristics 


It may be desirable in the case of important culverts 
to estimate as closely as possible the maximum amount 
of water that can be carried. Refinements in determina- 
tion of capacities are not worth while, of course, unless 
the maximum run-off can also be closely estimated—as 
when a watershed has been thoroughly studied to learn 
the effect of controlling factors. 


Entrance and outlet conditions may change capacities 
of short culverts materially and there is no precise way 
of taking them into account. The following formulas* 
result from careful experiments, however, and cover 
some of the usual conditions found in culverts. Basic 
conditions for all formulas are straight end-wall en- 
trances and culverts flowing full. 

Box culverts with square cornered entrances: 


Waa; 
j= AV 29H 


0.0045L 
y/1 + 0.4 R°3 + Ri 


Box culverts with rounded lip entrances: 


elt 
0.00451 
\/1.0s + Rie 


Concrete pipe culverts with square cornered entrances: 


Ne AV 29H 
0.026L 
1+ 0.31D°* + De 
Concrete pipe culverts with beveled lip entrances: 
ie AV 29H 
0.026L 
ia + pie 


In these formulas, 
Q = discharge in cubic feet per second 


A = cross-sectional area of opening in square 
feet 


g = acceleration of gravity (32.2 feet per 
second per second) 

H = head on culvert in feet (the difference 
between the elevation of water surface at 
inlet and at outlet, if the inlet is sub- 
merged) 

D = inside diameter of circular culvert in feet 


R = mean hydraulic radius (area of opening 
divided by wetted perimeter) 


L = length of culvert in feet 


It will be noted in the expressions that the discharge, 
Q, varies directly as the square root of the head, H, on 
the culvert. Applied to the case of overtaxed culverts 
during flood flows, this means that run-off will back up 
at the inlet until the head becomes great enough to 
provide the required culvert capacity. Advantage 
should rarely be taken of this fact, however, due to the 
damaging effect of stored water on the highway em- 
bankment. Saturation of fill material plus heavy lateral 
pressure may cause washouts and complete destruction 
of the culverts. 

For determining the discharge of small culverts it is 
customary to assume H equal to 0.5 ft. For large cul- 
verts, heads of 1 ft. or more may be assumed according 
to the judgment of the engineer. 

Quantitative effects of the various inlet and outlet 


conditions are discussed under ‘“‘Head Walls, Wing 
Walls and Cutoffs’’, page 50. 

To illustrate the use of the formulas, determine the 
capacity in cubic feet per second of the box culvert 
the area of which was computed by the Talbot Formula, 
page 10. 

Assume: H = 1.0 ft. 

area 


~ wetted perimeter’ 


L = 50 ft. 

A square culvert having an 
2120 
V/ 27.6 
For culvert flowing full and having a straight end 

wall and square cornered entrance, 


0 AV 29H 
0.0045L 
yi + 0.4 R°3 + pias 
27.6V 2 X 32.2 X 1.0 


0.0045 & 50 
\/1 + 0.4 & 1.3193 + p32 


175 cu.ft. per second 


opening of 27.6 sq.ft. gives R = SS Swie 


I 


Determination of Run-off by Other Methods 


In the design of drainage structures it is worth while 
to compute the maximum run-off by other methods to 
compare with the results obtained by the Talbot 
Formula. A well known formula which is used in the 
design of storm water drains and sewers is the Burkli- 
Ziegler Formula** : 


4 
i ye 
q = cr i 


in which: q = the water reaching the inlet in cubic feet 
per second per acre 
r = average rainfall intensity in cubic feet 
per second per acre during the heaviest 
rainfall, or rainfall intensity in inches 
per hour (approximately) 
s = general grade of drainage area in feet per 
thousand 
area drained in acres 
c¢ = empirical coefficient varying with the 
character of the surface 


The most serious limitation of this formula, as far as 
country watersheds are concerned, is in the selection 
of a proper value of c. Good results are obtained for 
cities by use of c equal to: 

0.75 for paved streets, 

0.625 for average areas, and 

0.31 for suburbs having lawns and unpaved streets. 
Values less than 0.31 will apply to country watersheds, 


*The Flow of Water Through Culverts, Bulletin 1, University 
of Iowa, Iowa City, Iowa. 

**For important analyses this method is supplemented by or 
replaced by more exhaustive and scientific studies. See ‘‘Run- 
Off—Rational Run-Off Formulas” by R. L. Gregory and C. E. 
Arnold, Transactions of the American Society of Civil Engineers, 
Vol. 96, 1932. 


I 


ll 


0.20 being used for average rural sections. Experience 
in the use of the formula is necessary, however, for 
intelligent estimation ofc for unusual types of watersheds. 


Example: Determination of Run-off by Burkli- 
Ziegler Formula 

Assume that maximum run-off is to be estimated for 
the watershed described on page 10, and those data not 
required by the Talbot Formula are made available. 


Given: 
r = 4.6 in. of rain per hour 


s = 50 ft. per 1,000 ft. (rolling land represented as 
having slopes of 5 to 10 per cent) 


a = 300 acres 
c = 0.20 


— 4 pe 


4 
S 30 
q= ne = 0.20 X 4.6 300 = 0.588 


Total run-off at inlet = qa = 0.588 X 300 = 176 cu.ft. 
per second. This compares with 175 cu.ft. per second 
for the culvert selected by use of the Talbot Formula. 
The close agreement should not be misinterpreted, how- 
ever, since the maximum slope for rolling land might 
have been used in the Burkli-Ziegler Formula instead 
of the minimum. On this basis (s = 100 instead of 50) 
the run-off would have been 


4 _—_ 
100 
q = 0.20 X 4.6 awe = 0.699 


Total run-off at inlet = 0.699 X 300 = 210 cu.ft. per 
second. 
Culvert Location 


Three important factors to be considered in the loca- 
tion of drainage structures for greatest efficiency and 
safety are alignment, slope and elevation. 


Alignment 


Proper alignment of a culvert must “‘fit’’ the structure 
into the surrounding topography. This means that the 
axis of a culvert should coincide with that of the stream 
bed. There should be a direct entrance to the culvert 
and also a direct outlet as any abrupt change disturbs 
and retards normal flow, cutting down the capacity of 
the culvert. Because of the decreased velocity, silt 
carried by the stream may be deposited, further reduc- 
ing the capacity. 


Slope 

In general, drainage structures should be built to the 
same slope as the stream bed in the vicinity. 

Disregard of the natural drainage slope may have 
serious consequences. A too flat culvert slope causes 
reduction in velocity of flow, thereby reducing the 
available capacity. Sedimentation induced by the low 
velocities gradually blocks the waterway during periods 
of normal flow to a point where any sudden storm flow 
might cause a complete washout. Conversely, a culvert 
slope greater than that of the stream bed may cause 
increased velocities high enough to erode and under- 


12 


mine the structure. 

One should appreciate the amount of erosion that is 
possible in different foundation materials. It is well 
known that the erosive power of a stream varies as the 
square of its velocity and, generally speaking, every 
material starts to erode at some definite velocity. 
Gradually increasing velocities are necessary for silt, 
fine sand, clay, gravel and boulders. 

Soft, silty bottoms of shallow streams start to erode 
at velocities less than 1 ft. per second, sand at 1 to 2 ft. 
per second, ordinary clay between 2 and 3 ft. per second, 
and compact clay or gravel between 4 and 6 ft. per 
second. In connection with study of the erosive powers 
of a stream, note that its ability to transport the eroded 
material varies as the sixth power of the velocity. Any 
change in the normal velocity of stream upsets the 
balance between erosion and sedimentation, and it is 
therefore important to maintain the stalus quo of well- 
established streams. 


Elevation 


Ordinarily, a culvert should be installed with the 
invert at stream bed elevation and not lower*. It should 
be remembered that a culvert will not pass more water 
than can be carried further downstream. Lowering the 
gradient at a culvert must be followed by cutting the 
channel downstream to the new grade and slope, if 
greater drainage is to be secured. This involves the 
correct solution of a hydraulic problem having many 
phases. 


Culvert Loads 


Loads on culverts are of two types—live loads and 
dead loads. Live loads include moving concentrated 
superloads, as truck wheel loads, with or without impact. 
Dead loads include weight of embankment material on 
culvert; weight of culvert and of contained water; 
lateral pressures on the sides of the culvert; and loads 
caused by hydrostatic pressures. The effects of these 
loads will be considered separately. 


Live Loads 


For design purposes, the maximum live load on 
culverts is taken as that produced by heavy trucks. 
In accordance with common practice, the standard 
truck train loading of the American Association of 
State Highway Officials will be adopted in this booklet, 
except that the width of traffic lane is taken as 10 ft. 
instead of 9 ft. Fig. 5 shows dimensions and loadings 
for both H-10 and H-15 truck trains. The H-10 loading 
is thought to be severe enough for design of structures 
on average secondary highways while the H-15 loading 
is used for heavily traveled secondary highways, and 
even for primary highways in most localities. 

Pressures from wheel loads are more uniformly dis- 
tributed on slabs when there is an intervening earth 
fill, On exposed slabs the action is different and this 
case will be discussed first. 


*Drop-inlet culverts are exceptions to this general rule. 


W=TOTAL WT.OF TRUCK AND LOAD 


I"PER TON OF W 
O.1IW 04 |W 
5 ASSUMED WEIGHT 
ON REAR TIRE= 


H-I5 TRUCK TRAIN 
H-10 TRUCK TRAIN 
114 TON TRUCK 


114 TON TRUCK 
1% TON TRUCK 
[be Seen 


114 TON TRUCK 
12 TON TRUCK 


1S TON TRUCK 
JOTON TRUCK 


SPACING OF TRUCKS IN TRUCK TRAIN 
Fig. 5. Modified A.A.S.H.O. truck train loadings. 


Wheel Loads on Exposed Slabs 


In assuming the ordinary position of a culvert trans- 
verse to a highway, it is obvious that only one truck 
of a truck train will be on a culvert at one time. Since 
two truck trains may be in adjacent lanes, however, 
the inside rear wheels of adjacent trucks are 4 ft. apart, 
center to center, on the slab*. The four rear wheels 
are placed near the slab support for computation of 
maximum shearing stresses and at mid-span for maxi- 
mum flexural stresses. The distribution of wheel load 
from the point of application to the slab supports is 
not subject to precise analysis in either case due to the 
complex structural action, but the results of careful 
tests and studies simplify the design procedure. The 
following is taken from one of these studies**: 


1. The distribution of shearing stresses in a slab 
under a concentrated load is independent of the 
magnitude of the load, within the range of working 
stresses. 

2. The effective width for maximum shearing stresses 
is independent of the span. 

3. When the load is placed closer to a free edge than 
3.25 WAR where ¢ = thickness of slab in feet, the 
effective width may be expressed as 

ee=nlt5 Male d, where d = distance of load 
from the free edge (line of support) in feet. 


The above statements refer to shearing stresses in 
slabs having freely supported edges. Culvert side walls 
are cast integrally with the slabs and are helpful in 
further distributing the load, as are fillets. In estimating 
a value of d for use in the formula, note that a wheel 
load is not concentrated at a point but acts over an 
oval area. The centroid of this area would be at least 


a foot from the inside face of wall support. To this 
add 1.5¢, to include helpful effect of integral supports 
and fillets. Then, 


for {= 0.5ft., e=1.75V0.5 + (I+ 1.5 X 0.5) = 2.99 ft. 
for {=1.0ft.,e=1.75V 1 +(0415X1) =4.25ft. 


These values are only rough approximations, so it 
seems reasonable to use an arbitrary effective width, e, 
of, say, 3.5 ft., for shear in culverts. Only one wheel 
load need be considered, since the minimum distance 
between adjacent wheels is 4 ft. 


The live load shear, Vz, based on H-15 loading (one 
rear wheel) is 
Vr = 0.4 X 15 X 2,000 (1 + 0.40T) 
= 16,800 lb. 


The dead load shear, Vp, for a strip, e = 3.5 ft. wide, 
will have a maximum value of about 1,500 lb., or, say 
10 per cent of V;. 


Assume allowable unit shear, v = 90 Jb. per sq.in., 
and allowable unit bond, u = 225 lb. per sq.in. 
Slab effective depth, d = = = CEE 
="5.0 1, Say. 10. 
Total thickness = 6 + 1.5 = 7.5 in. 
V 16,800 (1 + 0.10) 
uejd 225X3.5X %X 6 
= 4,5 in. perimeter per foot of width 


Similar computations based on H-10 loading show 
that a 5.5-in. thickness would be required. Arbitrarily 
setting a minimum thickness of 6 in. for exposed culvert 
slabs, d = 4.5 in., and required Zo is 4.0-in. perimeter 
per foot of width. 


These requirements are largely independent of span 
lengths, so they will be used herein as minimum values 
in the design of exposed slabs of culverts. Flexural 
stresses are also important, however, and must be 
considered. 


The moments produced by truck wheel loads applied 
at mid-span of exposed slabs have been studied in many 
investigations. In one of the most recent of thesef, 
formulas are given for mid-span moments due to four 
rear wheels in two adjacent 9-ft. lanes. Several different 
conditions are covered, those applying most directly to 
culverts being end restraint equal to 75 per cent of fixed 
end conditions and main reinforcement parallel to the 
direction of traffic. The following formula is based on 


Bond, Zo = 


*If 9-ft. traffic lanes were adopted, this distance would be 3 ft. 


**The Distribution of Shearing Stresses in Concrele Floor Slabs 
Under Concentrated Loads by M. G. Spangler, Bulletin 126, Iowa 
Engineering Experiment Station. 


. 50 : : 
tEffect of impact taken as Patan hs with a maximum value 
slightly less than 0.40. 


{Distribution of Wheel Loads and Design of Reinforced Con- 
crete Bridge Floor Slabs” by Erps, Googins and Parker, Public 
Roads, Vol. 18, No. 8, October, 1937. 


13 


these conditions, but applies to wheel loads on two 

adjacent 10-ft. lanes instead of 9-ft. lanes assumed in 

the investigation: 

(1.0+/) PS 

M = 07475 S + 20.80 

in which: M = live load moment in foot pounds per 
foot of width 


P = wheel load = 12,000 lb. for H-15 and 
8,000 lb. for H-10 loading 


S = effective span length in feet 
50 
125+8S 


I = impact factor = 


Determination of main reinforcement areas for the 
bottom face of the top slab is made from a total moment 
computed by adding to live load moment the mid-span 
moment due to weight of slab. Reinforcement require- 
ments in top of slab at supports may be considered the 
same. 

Part of the load is carried in slab action normal to 
the line of main reinforcement. The required reinforce- 
ment lengthwise of the culvert varies directly with the 
area of the main reinforcement and may be taken as 
45 per cent* of the latter. It should be located in the 
bottom of the slab parallel to the longitudinal axis of 
the culvert. If desirable, this reinforcement may be 
reduced one-third in the outer quarters of the span. 


Assume, to illustrate the formulas, that a one-cell 
box culvert having a clear span of 6 ft. is to carry H-10 
truck loading on exposed top slab. 


A 6-in. total thickness is adequate for shear, and 
negative reinforcement of outer face at corners must 
have a total perimeter of 4 in. per foot of culvert. 


The mid-span reinforcement, inside face of top slab, 
must resist a live load moment of 


VDE sd Wes 
0.7475S + 20.80 
50 
(1 =P 125 mene 0.4 X 10 X 2,000 X 6 
0.7475 X 6 + 20.80 
2,620 ft.lb. 


M,= 


2 


a 


105 


The dead load moment may be taken as 


6 
For a 6-in. slab, W = 75 X 150 = 75 Ib. per sq.ft. 


5 Oe 
10 
Design mid-span moment = M; + Mp = 2,620 + 270 
= 2,890 ft.lb. per foot of cul- 
vert 


This moment is used for computation of the reinforce- 
ment area and to check the concrete stresses in the 
6-in. slab. Design procedures are considered in a later 
section. 


14 


Wheel Loads on Covered Slabs 


Pressures transmitted through embankments by wheel 
loads have been carefully studied, and methods are 
available for their evaluation**. At the present time 
these methods require more time than the designer 
may want to spend, since the calculated pressures are 
small compared to those due to dead load. Approximate 
methods are ordinarily used, therefore, for quick com- 
putation of wheel load pressures. 

A reasonable approximation is to assume that a wheel 
load acts on the roadway surface on a line of length 
equal to the width of the tire. The pressure is assumed 
to be uniformly distributed on any horizontal plane and 
to spread out through the fill as illustrated in Fig. 6 
from which design pressures may be computed directly 
for various culvert sizes. This distribution is a slight 
modification of that used by the Iowa State Highway 
Commission. A discussion of the data upon which this 
diagram is based will indicate its adaptability to varying 
design conditions. 

In brief, the diagram applies directly to loads from 
moderate sized trucks (10-ton capacity) on roadway 
fills without pavement slabs. Due to the possibility that 


*See last footnote, page 13. 


**The Theory of External Loads on Closed Conduits in the Light 
of the Latest Experiments by Anson Marston, Bulletin 96, Iowa 
Engineering Experiment Station, lowa State College, Ames, Iowa. 


ASSUMED DISTRIBUTION OF PRESSURES ON TOP OF CULVERT: 


REA 
SRE Tre eaece 
- REAR WHEEL 
0.4x10T.x2000x1.50= 
me 12,000 * 
’ OR 
“10.4x15T. x 2,000" 
B 12,000* 
LONGITUDINAL SECTION CROSS SECTION 
Bce- OUTSIDE WIDTH OF CULVERT IN FEET 
4 6 8 10 \2 14 16 18 


2000 


ine 

soot we 
8 10 12 14 16 18 

Bc- OUTSIDE WIDTH OF CULVERT IN FEET 


Fig. 6. Wheel loads transmitted to culverts through fills. 


bumps might develop in such roads, 50 per cent impact* 
was included in the determination of pressures. The 
diagram also applies directly to highways having pave- 
ment slabs, under heavier trucks (15-ton capacity). No 
impact was included in this latter case, however, as it 
is quickly dissipated in acting through a stiff slab and 
cushioning embankment. The wider distribution of 
load because of the slab was also ignored, as were the 
effects of small loads from more distant front wheels. 
Note that fills deeper than 9 ft. are not shown on the 
diagram. Truck loads on deep fills have negligible effects 
compared to weight of embankment. 

Total live load on a culvert per foot of culvert length 
may be found by entering the diagram with the outside 
width of the culvert, proceeding vertically to the depth 
of fill on culvert and reading the value at the left margin. 
If, say, an 8-ton truck is assumed instead of a 10-ton 
truck on an unsurfaced road, multiply the diagram load 
value by 0.8. Similarly for other than 15-ton trucks on 
slab-surfaced highways, multiply load value by weight 
of truck in tons and divide by 15. If impact of any 
certain percentage is to be included in a particular case, 
compute an equivalent weight of truck in tons by adding 
in the impact, multiply the table values by this figure, 
and divide by 15. 


Dead Loads 


Pressures transmitted to culverts from embankment 
materials obey natural laws difficult of mathematical 
expression. The variable factors that represent soil 
characteristics—angle of internal friction, weight, homo- 
geneity of material, and per cent of contained moisture— 
can only be estimated roughly. The careful designer 
can direct his attention to only those combinations of 
conditions that may occur during the life of a culvert 
which would subject the culvert to the greatest probable 
pressures. A culvert designed for permanence should 
be capable of resisting these ultimate limiting pressures 
without distress. 

The theory of embankment pressures on culverts has 
been enlarged and improved in recent years, principally 
through investigations made by the Iowa Engineering 
Experiment Station in cooperation with the United 
States Bureau of Public Roads**. The Marston Theory, 
named for its originator, is generally accepted as the 
most logical approach to the problem yet advanced. 

In this theory the resultant vertical load on a culvert 
produced by an embankment is considered as made up 
of two elements: the weight of the fill directly above the 
culvert and the frictional forces acting either upward 
or downward due to the fill adjacent to the culvert. In 
the past only the first element was considered in esti- 
mating culvert load. The load in pounds per square 
foot was taken as the unit weight of the material in 
pounds per cubic foot multiplied by the depth of fill 
in feet. It can be shown that this procedure is too con- 
servative for some fill conditions and is unsafe for 
others. The frictional forces, which must be included 


in load determination, depend in magnitude and direc- 
tion upon the relative settlement of material adjacent 
to the culvert compared to that of material directly 
above. A greater settlement in material adjacent to the 
culvert, due perhaps to poor foundations or insufficient 
compaction, will set up frictional forces acting down- 
ward on the fill above the culvert. The resultant pres- 
sure on the culvert top is then greater than the weight 
of material above. If the settlement is greater directly 
above the culvert, however, the adjacent fill reduces 
the pressure on the culvert by the amount of the fric- 
tional forces—acting upward in this case. This latter 
phenomenon is commonly called “arching” of the em- 
bankment. Where there is no differential settlement 
between materials above and adjacent to a culvert, 
the resultant pressure is exactly equal to the weight of 
the material above the culvert. 


It is evident that the embankment pressures which 
culverts must withstand will vary between wide limits, 
depending on the type of embankment and the degree 
of compaction. A culvert built in a narrow trench in 
natural soil will probably never receive more than a 
small part of the weight of the embankment. On the 
other hand, if a culvert is built in a wide excavation, 
or projects above the natural ground level in an exposed 
position before the embankment is placed, care must 
be taken in compacting the backfill or high vertical 
pressures may be induced. 


The “bedding condition” of a culvert is also of great 
importance, not as it affects the magnitude of pressures, 
but as it influences the distribution of reaction pressure 
under a culvert. Careless or improper field construction 
methods may be instrumental in causing subsequent 
failure of a culvert under moderate loads. This applies 
particularly to circular conduits bedded in hard material 
not excavated to the shape of the conduit. Foundation 
pressures are thereby concentrated at one point, usually 
at. the lowest part of the conduit, producing much 
higher stresses than if the reaction had been distributed 
uniformly. 

Bedding conditions have been classified according to 
the care taken in excavating foundations to culvert 
shape and to degree of backfill compaction**. Fig. 7 
illustrates the different types of “projection bedding”’ 
of circular culverts ranging in severity from (a), imper- 
missible bedding, to the more favorable types (c), first- 
class bedding, and (d), concrete cradle bedding. Projec- 
tion bedding means that the culvert is bedded so that 
it projects into the embankment above the plane of the 
natural ground surface. 

For economical design of projecting conduits, first- 
class bedding is required. It may be obtained by bed- 
ding the conduit on fine granular materials in an earth 


*An arbitrary value determined by averaging suggested per- 
centages of several investigations. 

**The Supporting Strength of Rigid Pipe Culverts by M. G. 
Spangler, Bulletin 112; and The Theory of Loads in Ditches . . 
by A. Marston and A. O. Anderson, Bulletin 31; Iowa Engineering 
Experiment Station, Ames, Iowa. 


15 


EMBANKMENT as aera geo 
Bc= OUTSIDE 

DIAMETER 

OF PIPE 


Rae 


WROTE SHALLOW Sy 
NOT SHAPED EARTH CUSHION 


TO FIT PIPE 


a) IMPERMISSIBLE BEDDING 


ACCURATELY SHAPED TO FIT PIPE 


(C)FIRST CLASS BEDDING —_(d) CONC. CRADLE BEDDING 


Fig. 7. Four types of projection bedding for circular pipe. 


foundation carefully shaped to fit the lower face for at 
least 10 per cent of the over-all height (of circular con- 
duits) and by thoroughly ramming and tamping the 
backfill in layers not thicker than 6 in. around the 
conduit for the remainder of the lower 30 per cent of 
the height. On rock foundations an earth cushion having 
a depth at least equal to that shown in Fig. 7 (b) is 
also required. 


The use of a concrete cradle is ordinarily reserved 
for circular pipe conduits under very high fills. 


Bedding conditions comparable to those achieved by 
first-class bedding are readily obtained with box cul- 
verts and other types of conduits having relatively flat 
bases. It is desirable, however, to bed such conduits on 
carefully shaped natural foundations or well compacted 
granular material, and to backfill the sides in the man- 
ner described for first-class bedding. 


Special Requirements in 
Construction of Large Culverts 


The development of a painstaking technique in com- 
pacting embankments is worth while for even small 
culverts and is especially important for large, heavily 
loaded structures. State highway departments are 
approaching a unanimity of opinion in specifying careful 


16 


construction procedures, a typical specification being 
as follows: 


Placing Embankment Below Top of Culvert 


Selected embankment material (preferably clayey 
loam, sandy loam, or sand, gravel and clay mixture) 
free from rocks, ¢lods or frozen lumps shall be placed 
alongside the culvert in layers not exceeding 6 in. 
in thickness, and each layer shall be thoroughly 
compacted by hand tamping, by tamping with 
mechanical rammers, by rolling, or by other approved 
means, for a distance of not less than the external 
diameter of the culvert on each side thereof; except 
that in trench construction the compaction shall be 
carried out for the full width of the trench. Each 
layer of embankment material, if dry, shall be mois- 
tened before being compacted. Special care shall be 
taken to compact the embankment under the lower 
one-half circumference of circular pipes. 


Placing Embankment Above Top of Culvert 


Ordinary Method: 


Unless otherwise specified the embankment above 
the culvert shall be placed in successive layers, 
approximately horizontal and not more than 12 in. 
in thickness when compacted, and extending the 
full width of the cross section. Each layer shall be 
kept level and bladed smooth before the succeeding 
layer is placed, and shall be compacted by a tamping 
roller over its entire surface area until there is no 
further decrease in the depth of penetration of the 
tamping feet of the roller. 


Loose Backfill Method: 


Where this method is specified, the embankment 
shall be constructed as by the ordinary method, to 
a depth above the culvert equal to the height of 
culvert. That portion of embankment directly above 
the culvert shall then be excavated, keeping the 
sides as nearly vertical as possible, and the resulting 
trench shall be backfilled with loose material. The 
balance of the embankment shall then be con- 
structed as by the ordinary method. 


It can be seen that the “loose backfill” method is used 
to obtain slightly greater settlement in a vertical section 
extending through the culvert than in similar sections 
adjacent and parallel to the culvert. The embankment 
load on the culvert is thereby reduced by the “arching” 
action, previously described. This special method is of 
no avail when embankment material is sand or gravel, 
and cannot be used in very shallow fills. 


A point to note in connection with any method of 
backfilling is to keep the width of trench or excavation 
to the bare minimum required for construction of cul- 
vert. Unexcavated material is usually more compact 
than backfilled material. It is also advisable to have 
backfilling proceed simultaneously on both sides of a 
culvert so that unbalanced pressures will not be pro- 
duced. A culvert may be subjected to more severe 


pressures during the placing of embankment than at 
any later time. The most common cause of this is the 
impact of large quantities of material falling from a con- 
siderable height directly on or adjacent to the structure 
during backfilling; or the weight of heavy equipment 
traveling back and forth over thinly covered conduits. 
Such practices should not be tolerated. 


Vertical Load 


The total vertical load per linear foot on a projecting 
conduit due to an embankment may be determined by 
the formula 

P = C.wB? 
weight of fill material per cubic foot 
outside width of the conduit in feet 


coefficient depending on depth of fill, 
H, above conduit; width, B,; projec- 
tion of the conduit above natural 
ground surface; and the character of 
the fill material 


The variable factors that control C,* are not suscept- 
ible to determination in the field and it gradually 
changes in value. The designer is forced to assume a few 
limiting conditions of varying degrees of severity so that 
he can determine maximum loads severe enough for and 
applicable to particular locations. 


Three general cases have been selected to cover design 
requirements. All are based on the supposition that 


in which: w 
Be 
Ce 


Ww 
oO 


¥ ROADWAY SURFACE 
2 ee=00 


SSS SSISSES NATURAL 
SS | GROUND 
SSRs <i SURFACE 


& 


NATURAL fQ==Se==— |] 


32 


26 
NOTATION 
21 ur = JOO LB. PERCULFT. AY 
Ba = WIDTH OF TRENCH (FT, as 
2o|_—H = DEPTH OF FILL OVER CULVERT (FT.) g 
a'= COEFF. OF SLIDING FRICTION +0 


=TAN.30°O.577=u 4 


18 
bs 
op 2 ee » pr 
IG Ks [paz+] + AL ge at 
: a 
1d 0.333 i ot 0 
| Ks ey 


TOTAL VERTICAL LOAD ON CONDUIT IN KIPS PER LINEAR FOOT 
™ 
a 


l2 : 


P 
iS 
eo 


- fe) 8 10 l2 14 IG 18 
Ba= WIDTH OF TRENCH IN FEET 


Fig. 8. Vertical pressures on conduits from fills. Case I. 


bedding conditions equivalent to first-class bedding are 
obtained. 


CASE I, Fig. 8, gives the total vertical load in kips 
(1,000-Ib. units) per linear foot on conduits completely 
buried in deep narrow trenches excavated in com- 
paratively solid material and with fill around the con- 
duit carefully compacted. The load given is the maxi- 
mum to be reasonably expected under these very 
favorable conditions. 


CASE II gives the total vertical load on conduits pro- 
jecting partly above the natural ground surface, and 
protected on the sides by an old compacted fill at least 
to the top of the conduit. This type of loading is the 
one most commonly assumed for large culverts, the 
load per square foot being equal to the unit weight of 
the fill material multiplied by the depth of fill above 
the top of culvert. No diagram is presented for this case. 


CASE III, Fig. 9, gives the total vertical load on con- 
duits projecting entirely above the natural ground sur- 
face or in wide excavations having flat side slopes. Com- 
paction of fill material at the side of the conduit is 


*Several complicated expressions are available for the deter- 
mination of C; to cover all the possible combinations of variables. 
Reference is made to Iowa Engineering Experiment Station 
Bulletins 31 and 112 for those wishing to investigate the subject 
further. 


NY SURF PACTED e UL l 
40; ere eee Z Vea 
= = = ve - | 
O38 Lv | We : 
j 36/" - [pres 
es NATURAL GROUND __4” wa 
a 
Zz 34 SURFACE ne) 4 
=~" [THOROUGHLY COMPACTED BACKFIL ae 
as 32 ee: H_H 4 oo 4 
w) + ae : 
a. C= +2Kye Aue Be ie as ~ eo (Zz c= 
a0 s2kute _ He. mr . iP 
z e*cM* ae - CK B. tCKM reap + } 1O be A DA 
| 4 L L Le 
S06 (SEE CASE I) [a7 a 
Qa 
= L | ‘ A ea 
S zat 4 a Be aie eel 
= co) 
ama ea ees 
We ere ee ae 
g 20 ATs A Za M6 LA] 
= fff \ 
1 eueaeea A 
a A 4 
E ZAZLZ seed ees 
ar 7 tle ae | ee On ee | 
5 aZ oe ava 
- VW, < = A — | 
al aol aa Ze) es 
eal eee | Os Ok S| 
4 oem et ee een 
eee eat eerie eat fen 
6 eee ee ao GG 
ae Leia els 4 3 Sa 
4 es es Le Se 
; (ees ar En ee 
° GT eS Ee ee ee ee 
4 6 8 10 8 


l2 14 1G 
Bc= OUTSIDE WIDTH OF CONDUIT IN FEET 


Fig. 9. Vertical pressures on conduits from fills. Case III. 


17 


especially important in this case to build up lateral 
restraint. This case is the most severe of the three and 
is used in locations where controlling conditions are 
unfavorable. 


In all three cases the vertical load is considered uni- 
formly distributed over both circular and flat top con- 
duits. In Case I, however, the width of the trench is 
used instead of the outside width of the conduit. Where 
the sides of the trench slope outward slightly the hori- 
zontal width at the elevation of top of conduit is taken. 
In either instance, the sides of the narrow trench must 
not be farther from the conduit walls than is required 
for placing forms or Case I will not apply. 


It should be remembered that the design loads given in 
the diagrams may not be reached for years in a par- 
ticular location. The loads are the most severe that can 
be reasonably expected under the basic conditions. If 
unusual conditions capable of producing extremely high 
loads are anticipated, Case III should be used. 


Depths of fill greater than 24 ft. are not included in 
the diagrams as the fundamental equations were based 
on small culverts under low fills and may not apply to 
high fills. It is reasonable to assume that for most field 
conditions the actual vertical pressures under high fills 
are considerably less than those given by Case II or 
Case III, due to arching action. 


Examples on Use of the Diagrams 


Assume that a culvert with a total width, outside to 
outside, of 8 ft. must carry a fill 14 ft. high above top of 
culvert. Fill material is assumed to weigh 100 lb. per 
cu.ft. 


CASE I: Under the favorable conditions upon which 
Fig. 8 was based, the total load in kips (1,000-lb. units) 
per linear foot of culvert would be found as follows: 
Assume a width of trench 2 ft. greater than the width 
of culvert (allowing 1 ft. clear each side). Enter Fig. 8 
with Bg = 10 ft., proceed vertically to the intersection 
with the diagonal line representing 14-ft. cover and then 
horizontally to the left margin. The total load is 10.8 
kips. 


CASE II: For average, not particularly severe condi- 
tions Case II might be assumed. The total load then 
equals 
100 X 8 x 14 
1,000 


No diagram is necessary as the total load is equal to the 
weight of the prism of earth directly above the culvert. 
The total load would be the same for a circular culvert 
of the same outside width, as the depth of fill is taken 
as the depth above the culvert at the crown. 


= 11.2 kips. 


CASE III: For unusually severe conditions Fig. 9 
would be used. Entering the diagram with B, = 8 ft. 
and cover of 14 ft., the total load is found to be 15.9 
kips. 


18 


These examples indicate the range in embankment 
load due to different conditions. For a unit weight of 
fill other than 100 lb., divide the total load by 100 and 
multiply by the proper unit weight in pounds per cubic 
foot. 


Table II gives average weights of different types of 
embankment materials. 


TABLE II. Average Weights of Embankment 
Materials in Pounds per Cubic Foot 


Dry earth (loose) 


Dry sand; dry packed earth; damp top soil; 
dry clay and gravel 


Saturated top soil 


Wet sand; damp clay; wet sand and gravel 


Lateral Pressures 


In the design of unimportant culverts the existence 
of lateral earth pressures is sometimes ignored since 
they counteract and relieve stresses due to vertical 
pressures. Any helpful effect of lateral pressures has 
been considered an additional factor of safety in the 
design, but such procedures unnecessarily penalize 
earth supporting structures in the usual cases where 
lateral forces are known to act. 


Lateral pressures in embankments are of two dis- 
tinct types: aclive pressure and passive pressure. Active 
pressure on culverts is caused by the action of the 
embankment in attempting to assume its natural con- 
dition of repose—that is, its natural slope or angle of 
repose. Passive pressure is induced by the movement of 
a structure against the supporting material. Its magni- 
tude is a function of the amount of movement and also 
of the soil characteristics. Because of its indeterminate 
nature and changeable, uncertain magnitude, passive 
pressure is rarely depended upon to relieve stresses from 
more positive causes. Active lateral pressure is a direct 
function of vertical pressure, however, and may be 
estimated with fair accuracy. 


By Rankine’s Theory the intensity of active lateral 
pressure is equal to K times the intensity of vertical 
pressure, and 
> Vee 

Veale 
in which u is the coefficient of internal friction of the 
material. The coefficient may be expressed as 

pw = tan ¢ = tangent of the angle of repose, ¢ 

Angles of repose of different materials have been care- 
fully determined by laboratory methods. Unless it is 
considered desirable to make precise tests, however, 
the angle of repose for average fill materials may be 
assumed as 30 deg. This is usually satisfactory since K 
is little affected by large changes in ¢. 


K 


For é = 30 deg., K equals 0.333, and the intensily of 
active lateral pressure at a point in an embankment is 
then equal to one-third the intensity of vertical pressure. 
Note that Figs. 8 and 9 were based on w = tan 30 deg. 
= 0.0/1,and K = 0.333. 


Estimation of the magnitude of active lateral pres- 
sures and the decision as to whether such pressures 
should be used in a design are usually matters of judg- 
ment based on consideration of the character of the back- 
fill and the ditch conditions. For example, if conditions 
are such that Case I may be used for determination of 
vertical pressures on rectangular box culverts, it should 
be apparent that only low active pressures can be 
assumed. The narrow trench, excavated in solid mater- 
ial, allows no opportunity for sizable active pressures to 
build up. For Case I, then, no active pressure should be 
assumed in design of rectangular culverts. It is also 
evident that conditions of Case II and Case III are 
more favorable for the development of active pressures 
and, therefore, they should be taken into account. 


In the case of circular or arch culverts it is obvious 
that large active lateral pressures exist. Radial forces 
have horizontal components on the curved surfaces, on 
top as well as bottom of the structures. This is especially 
true in the case of well compacted backfill, or in 
saturated backfill where lateral pressures may approach 
hydrostatic conditions. Embankment conditions change, 
however, and the combination producing minimum 
lateral pressures should be assumed for design. Inten- 
sities equal to one-third the intensities of vertical 
pressures are low enough to meet average requirements. 


Flexible pipe culverts present a more complicated 
problem than those just described. Due to lack of 
rigidity, such pipes deflect inward at crown and invert 
under embankment loads and outward at the horizontal 
diameter. The inward vertical deflection reduces the 
load carried by the pipe because of arch action in the 
embankment. This is only temporary, however, as 
internal forces in the embankment induced by the 
deflection are relieved by sliding and readjustment of 
particles as the embankment seeks a more stable con- 
dition of equilibrium, assisted by ‘“‘shaking down” from 
vibration caused by traffic. Gradually the load builds 
up, increasing the deflection of pipe and starting a new 
cycle. This may continue indefinitely, the deflection 
becoming greater and greater due to the shifting load 
and due to the fact that each increment of deflection 
reduces the capacity of the pipe to resist deflection— 
that is, reduces the rigidity of the pipe. 

As the pipe deflects vertically the sides at horizontal 
diameter distort outward, developing some degree of 
lateral restraint due to passive pressures. This restraint 
can only be depended on in locations where the backfill 
is compact, relatively incompressible and protected 
from moisture or other conditions that might reduce 
its effectiveness. It is important to realize, also, that 


when the deflection causes the top of the pipe to reverse 
its curvature—becoming concave upward—the sides of 
the pipe pull in. Passive lateral support is thereby 
eliminated and the pipe proceeds rapidly to collapse 
and complete failure. 


Flexible pipe culverts designed from the results of 
short-time load tests, or for locations exposed to any of 
a number of changing conditions, require internal 
bracing, repair or replacement within a few years. 
Vibration of embankment due to traffic, moist backfill, 
and drying and shrinking of material away from sides of 
the pipe all hasten collapse. 

The phenomenon of increasing deflection in flexible 
pipes without material increase in total load has been 
noted in long-time load investigations. In one of the 
most recently published of these investigations, deflec- 
tions of a 42-in. flexible pipe were studied over a period 
of years*. 

In December, 1927, at completion of the fill the verti- 
cal deflection was 1.43 in. under a load of 5,300 lb. per 
lin.ft. of pipe. 

In August, 1932, the deflection was 2.44 in. and the 
load was 6,800 lb. per lin.ft. of pipe. 


In September, 1937, the deflection was 2.62 in. and 
the load was 6,400 Ib. per lin.ft. of pipe. 


As a result of his investigations, Spangler made this 
statement: 


“The fact that flexible pipes continue to deform 
slowly after the fill is completed is in all probability 
analagous to the widely known fact that all struc- 
tures resting on earth foundations continue to settle 
long after the maximum load on the footings is 
applied. Apparently the fill material at the sides of 
the pipes slowly recedes in response to the pressure 
acting between the pipe and the fill and this per- 
mits the pipe to deflect even when there is no 
increase in the vertical load. This phenomenon may 
be of importance in supplying data upon which 
specifications for flexible pipes can be based. The 
deflection at the time of fill completion should 
possibly be specified for practical reasons; but this 
specified deflection should be related to the ultimate 
deflection, which may occur years later and which 
determines the load capacity of the pipe.” 


In the design of reinforced concrete culverts it is not 
necessary to rely on passive lateral pressure for aid in 
withstanding embankment loads. Therefore, the ten- 
uous nature of such pressure is of no significance to the 
designer. He can determine the greatest probable verti- 
cal pressures with fair accuracy and can then design a 
culvert with confidence, utilizing, as he does, the in- 
herent rigidity and recognized strength of reinforced 
concrete. Lateral passive pressures are entirely ignored. 

*“The Structural Design of Flexible Pipe Culverts” by M. G. 
Spangler, Iowa Engineering Experiment Station, presented in 
Public Roads, Vol. 18, No. 12, February, 1938. 


19 


Choice of Culvert Shape 


Selection of culvert shape should be carefully made, 
as the best shape depends upon such factors as topo- 
graphy of site, importance of hydraulic and structural 
efficiencies of available types, familiarity of the builder 
with construction procedures, and cost. 


It is important, first, to choose a culvert shape that 
will best fit the waterway of the drainage channel. In 
narrow deep channels likely to carry high flows during 
the rainy season it is usually cheaper to install tall 
comparatively narrow culverts to fit the natural water- 
way than to use wide, low structures. The latter type 
will require heavy excavation in the sides of the channel 
and more elaborate head walls and inlet transitions. 
On the other hand, in flat areas having no well defined 
waterways, the flood flow may be large in volume but 
of shallow depth. Unless water is allowed to back up— 
undesirable for many reasons—the capacity of a cul- 
vert above the flood level will be entirely wasted. A 
wide box culvert consisting of several cells or openings 
is better for these conditions. 


Where hydraulic efficiency is important, as in the case 
of long culverts or storm drains, the superior features of 
circular concrete culverts are deciding factors. For a 
given perimeter, a circular section has the greatest area 
of any shape, which means maximum economy of ma- 
terials. Furthermore, for a given area:a circular section 
will give the greatest flow due to the larger hydraulic 
radius (area divided by wetted perimeter). There is 
also less interference and disturbance of flow through a 
smooth circular bore than through other shapes. A 
factor in favor of box culverts occurs where wing walls 
or other transitions are required, as such appurtenances 
may be easily designed to permit a greater reduction in 
entrance losses than for circular culverts. 


Scene along the Natchez Trace near Jackson, Miss. The 
culvert has curved wing walls and a rounded opening 
for hydraulic efficiency. 


20 


The structural properties of culverts are important 
and varied, making it advisable to consider the different 
types separately. 


Box Culverts 


One of the principal reasons why box culverts have 
gained so in popularity over other cast-in-place types is 
because of the simplicity of their construction. Inex- 
pensive forms may be used, placement of reinforcement 
is not difficult, and contractors can use methods little 
different from those learned through experience in 
ordinary building construction. These facts are im- 
portant, but it should be pointed out that much of the 
hesitation toward unusual construction as, say, sewer 
construction, is without real foundation, and disappears 
with a little experience. 


Box culverts are most suitable for average condi- 
tions, comprising moderate or low fills. As embankment 
loads increase, box culverts become less economical. 
This is also true when internal hydrostatic pressures 
become greater than external loads. Culverts of several 
cells are adapted to moderate embankment fills and 
requirements of large waterways. A great advantage of 
this type, and the single box as well, occurs when a 
roadway grade is fixed and headroom is restricted. 
Sufficient waterway opening is made by using a wider 
structure to make up for loss of height. 

Square boxes are ordinarily designed up to, say, 10-ft. 
span for deep flows if there is sufficient headroom. 
Often, however, the depth of flow is comparatively 
shallow and required waterway openings must be 
obtained' by use of wider structures. Culverts of two, 
three or more cells are better for such locations. 


Superior foundation conditions are achieved by box 
culverts for nearly any type of foundation material. 
In unstable compressible materials of low bearing 
capacity, the pressures are distributed more uniformly 
and over a wider area than for other types. Settlement 
is less likely and therefore the possibility of highway 
depressions is reduced. On rock foundations the thick- 
ness of the bottom slab may be reduced, or perhaps 
entirely eliminated by use of small footings. Compare 
this with the unfavorable action of rock foundations 
under inverts of circular culverts not properly bedded. 


Modified Circular Culverts and Conduits 


Cast-in-place culverts having a circular bore are most 
economical when used under high embankment fills 
where heavy pressures are anticipated. They are sat- 
isfactory for a wide range of conditions, including con- 
duits subject to internal hydrostatic pressures. 

The uniform bearing under the base slabs of box 
culverts and the wide distribution of load may be 
obtained by designing the lower face of a circular culvert 
relatively flat. This also provides greater thickness and 
strength at the sides to transmit the large thrusts 
uniformly to the foundations, and less thickness at the 
invert to resist the smaller shears and pressures. 


This multiple box culvert meets both hydraulic and structural requirements in the countryside of Tarrant County, 
Texas. Note the parallel wing walls, required because of restricted right-of-way. 


Fig. 10 illustrates a cross section of conduit that is 
widely adopted for the special conditions just described. 
The shape has the hydraulic values of a circular tube, 
the load carrying qualities of a circular arch, and the 
flattened base so desirable in the box culvert. The 
standard section shown in Fig. 10 is designated as 
Type I for convenience. It may be used economically 
for many purposes, including inverted siphons, storm 
drainage conduits, sewers and culverts. 


Reinforcement 
not shown 


Fig. 10. Cross section—Ty pe I conduit. 


The design of Type I conduits is considered in a later 
section, and typical designs for various conditions are 
also presented. 


A further modification of the circular type is desirable 


under very heavy fills, or when the vertical loads are 
moderate but lateral restraining pressures are too small 
to be effective in reducing moments. In such cases the 
most economic type has a parabolic or multi-centered 
top making a more pronounced peak than the circular 
type. This shape more nearly conforms to the pressure 
line of resultant loads and therefore a greater part of 
the load is carried as direct thrust, without producing 
large bending moments. High moments and shears 
would be produced in box culverts under similar load 
conditions. Thinner sections may be utilized for the 
upper part of conduits than would be safe for box 
culverts. 


The unusual load conditions outlined above are 
rarely met in culvert design, but are quite common in 
design of sewers or storm water drainage conduits. 
Many types of sections have been recommended for 
such conditions and because of important hydraulic re- 
quirements*. No attempt will be made here to cover 
the various sewer types available. Each type has par- 
ticular advantages and disadvantages, depending on 
the importance of its structural or hydraulic features. 
Several, including the horseshoe, parabolic, semi- 
elliptical and egg-shaped types, are especially effective 
in carrying heavy vertical loads and in maintaining 
good hydraulic conditions no matter what the depth of 
flow. Many of their respective advantages are gained by 
designing the lower part of the cross section the same 
as Type I, Fig. 10, and by making the upper part a 
three-centered arch of varying thickness. 


*See any standard text on sewerage practice such as American 
Sewerage Practice, Vol. I, ‘““Design of Sewers” by Metcalfe and 
Eddy, McGraw-Hill Book Co., New York. 


21 


The modified section, designated as Type II in Fig. 
11, is recommended for large conduits having some or 
all of the following conditions: 


1. Heavy vertical loads 

2. Moderate or small lateral pressures 
3. Deep, narrow drainage channels 
4 


. Requirements for hydraulic efficiency (as for 
long conduits on flat gradients) 


5. Little or no internal hydrostatic head above con- 
duit crown 


Reinforcement 
not shown 


Fig. 11. Cross section—Type II conduit. 


The requirement against high internal hydrostatic 
head refers to the most economic designs, as com- 
pared to Type I conduits. Pressures due to hydrostatic 
head above conduit crown produce tension only on 
circular sections and may easily be resisted; on non- 
circular sections, however, moment and shear are 
induced as well, and heavier sections are required. 
For this reason, Type I conduits are superior to Type 
II for locations giving high internal hydrostatic heads. 

In sewer or storm drainage systems it is not uncom- 
mon for deep excavations to be necessary. The width 
of conduit then becomes an important factor in excava- 
tion costs. Depths of fill on conduit may also be con- 
siderably greater than 15 ft.; and the designer may feel 
that backfill material is of such quality that active 
lateral pressures will be only, say, 20 per cent of the 
vertical pressures, rather than 33 per cent or more. 
Type II conduits meet all these requirements ad- 
mirably, and very worth while savings in concrete and 
reinforcement can be gained in comparison with box or 
Type I conduits. 


22 


Design Loads and Procedures 
Loads 


Culverts and conduits may be subjected to many 
combinations of loads, but it is convenient for design 
purposes to consider each load separately. 

The position of the culvert relative to the roadway 
surface is considered first. If the top slab is to carry 
traffic loads directly without any embankment cover, 
the design loads are as discussed on page 12. For H-10 
truck loading plus impact, the top slab must be at least 
6 in. thick to resist shear, while an 8-in. minimum 
thickness is required for H-15 loading plus impact. 
These dimensions are based on the allowable stresses 
given on page 26. Foundation reactions to the truck 
loads are distributed in a manner difficult to estimate, 
and lateral loads are small and indeterminate. Because 
of this, it is common practice in the design of small cul- 
verts having exposed top slabs to arbitrarily make the 
slabs and side walls the same thickness. 

The design of buried culverts or conduits is more 
involved since vertical and lateral pressures have 
various relationships and magnitudes. 

The total live load on the culvert top, assumed to be 
uniformly distributed, is obtained from Fig. 6, page 14. 
This includes effect of impact and static loads through 
fills from a 10-ton truck on roads not having slab pave- 
ment; and is equivalent to loads through fills from a 
15-ton truck on slab-surfaced roads. 

Vertical load from embankment fill, also assumed to 
be uniformly distributed, is obtained for one of three 
general conditions represented by Case I, Fig. 8; Case 
TI; or Case III, Fig. 9, page 17. 

The loads from these diagrams are used without 
modification on either flat-top or curved-top culverts. 
The foundation reactions due to the loads are equal, 
of course, to the vertical loads, but their distribution 
across the base of culvert varies with its type. The heavy 
side walls of Type I and II conduits carry the thrust 
to the foundation so that most of the reaction is con- 
centrated directly beneath, and less under the invert. 
For symmetrical culverts the foundation pressure dia- 
gram of each half may be represented conservatively 
by a trapezoid. In the following sections on design of 
Type I and Type II conduits, this trapezoid of founda- 
tion pressures is assumed to have a vertical ordinate 
under centerline of invert equal to one-half the vertical 
ordinate at the outer side. 

The usual practice in design of box culverts is to 
assume vertical load reactions uniformly distributed 
on the bottom slab. Moments are not much affected by 
different conservative assumptions as to foundation 
pressure distribution, so uniform distribution is assumed 
herein for box culverts. 

Weight of the culvert itself, empty, is next con- 
sidered. Distribution of pressure depends on the shape 
of the section considered. 

Active lateral pressures are assumed to be symmetri- 
cal on both sides of a culvert, as care in backfilling will 


View of culvert inlet 
near Selma, Miss. 
An effective transi- 
tion was achieved by 
stabilizing side 
slopes with two 
types of concrete 
revetment—slabs on 
the lower portion 
and riprap above. 


permit no large unbalanced pressures. Of course, the 
large factor of safety in the design will take care of 
considerable variation in lateral pressure, should that 
occur. 


Lateral pressure is computed in terms of equivalent 
fluid pressure. Its intensity depends on several factors, 
as previously discussed, but is usually taken as one- 
third the vertical pressure at the point. The load dia- 
gram is trapezoidal in shape and can be separated into 
uniform and triangular loading diagrams. 

External lateral pressure partially counteracts verti- 
cal loads and therefore should be considered when it is 
known to act. Often its magnitude can only be estimated. 
Some engineers assume lateral pressure only 20 per 
cent of the vertical pressure, or even less, and ignore 
pressures caused by water within the conduit. It is 
more precise, and usually safer, to assume lateral 


anaes 


Fig. 12. Load pressure diagrams. 


pressure equal to one-third the vertical pressure at the 
point; and to consider the opposite action of internal 
hydrostatic head. 

Pressures due to internal head are best handled as two 
separate conditions: the first caused by water com- 
pletely filling the conduit, and the second by internal 
hydrostatic head above the crown. The latter condition 
may ordinarily be ignored in culvert design, if it is only 
temporary. 

The above loading conditions are divided into six 
classifications as follows (see Fig. 12): 


I. Uniform vertical load, represented by P. 
P = total embankment and truck load on the 
culvert, in pounds per foot of culvert length. 


II. Weight of culvert (uniform reaction assumed), 
given in pounds, and based on weight of 150 
lb. per cu.ft. of concrete. 


III. Pressure from contained water to top of cul- 
vert, given in pounds, and based on weight of 
62.5 lb. per cu.ft. of water. 

IV. Uniform lateral load (symmetrical on both 
sides), represented by w. 
w = lateral pressure at top of culvert in pounds 
per square foot. 

V. Triangular lateral load (symmetrical on both 
sides), represented by T. 


T = equivalent lateral unit pressure, pounds 
per square foot. 


(A combination of IV and V will give any 
desired trapezoidal type of lateral loading.) 


VI. Internal hydrostatic pressure due only to head 
above top of culvert. (Equal to 62.5h, lb. per 
sq.ft. on inside faces, where h is the hydro- 
static head in feet above inside top of culvert. 
(VI is common only in the design of pressure 
conduits, and may be ignored in ordinary cul- 


vert design. When used, it is only in connection 
with III.) 


23 


The loads are kept separate so that internal stresses 
may be determined for each. Moment, thrust and shear 
coefficients at critical sections can then be tabulated 
in terms of symbols representing each type of load, 
various inside dimensions of opening and various 
thicknesses of section. It is convenient to compute all 
loads per linear foot of culvert. When all coefficients 
are summed, the resisting section is then 12 in. wide. 

By use of these coefficients the designer can quickly 
determine moments, thrusts and shears at critical sec- 
tions by substituting numerical values for loads and 
dimensions to fit his particular case. Detailed explana- 
tion and examples on the use of the coefficients are 
given later for each type of structure. 


Design Considerations 


Appreciation of the economies to be gained by care- 
ful design of box culverts has encouraged improve- 
ments in methods of analysis and design. Although 
formerly not the case, box culverts are now designed 
as precisely as sewers or pressure conduits. Design 
considerations to be noted include the following: 

Due to continuity of the cross section of box culverts, 
mid-span moments are reduced from those in simple 
spans and provision must be made for the tension pro- 
duced by negative moments at outside faces adjacent 
to corners. Side walls are designed to resist bending 
moment combined with axial thrust, and shear due to 
lateral loads. Top and bottom slabs are designed for 
bending moment, with small thrusts ignored, and for 
large shears due to vertical loads or reactions. 

Where critical sections are at faces of supports, 
corrections should be made to computed moments at 
the centers of supports to give the correct design 
moments. In Tables [V and IX the support moment 
coefficients have been adjusted to faces of supports on 
the conservative assumption that thickness, ¢, of sup- 
port equals one-twelfth the clear span, L. The possible 
error in adjusted values by this assumption is negli- 
gible. Shears at faces of supports are only slightly 
smaller than corresponding shears at centers of sup- 
ports, so shear adjustments are not usually made. 

The capacity is reduced only an insignificant amount 
by chamfering the inner corners of a box culvert—even 
less in per cent than the corresponding reduction in 
culvert area produced by the chamfering. Since fillets 
aid in eliminating regions of high localized stress at 
corners of box culverts and other continuous struc- 
tures, they should be used. Good practice calls for 
progressively larger fillets as the spans increase, up 
to 6-in. fillets (measured horizontally and vertically 
from the corner to face of fillet) for the bigger box 
culverts. Very large fillets are more properly termed 
haunches, and the design should include the effects of 
the increased sections at ends of members. Unless they 
have been taken into account in the analysis, however, 
fillets should be ignored in the design of sections. 

The most critical sections in buried box culverts for 
usual spans and loads will occur in the bottom slab at 


24 


mid-span and at faces of supports. The minimum con- 
crete thickness may be controlled by the effective depth 
necessary to resist positive moment at mid-span, or by 
shear or bond requirements at the supports. Bond 
stresses may be high at the latter points even though 
shear stresses are satisfactory. Negative reinforcement 
in excess of that required for moment may then be 
required. 

The change in moment stress from tension on inside 
faces at mid-span to tension on outside faces at corners 
makes two layers of reinforcement necessary at many 
sections. Most of the steel requirement can be satisfied 
by bending half of the positive moment reinforcement 
to the outer face near supports where it may act as 
negative reinforcement. For small culverts it is usually 
cheaper to eliminate complicated bends in reinforce- 
ment, and to use straight bars for positive moment and 
short L-bars for the outside faces at corners. 

It will be noted in the design of rectangular culverts 
of some proportions that the lateral loads are not large 
enough to produce tension on inside faces of side walls. 
In other words, the resultant moment at mid-height 
may be negative because of large vertical loads on the 
culvert. Reinforcement is then required for the outside 
faces of side walls over the entire height. The effect 
of axial thrust cuts down the amount required. 

In the design of wall sections, advantage should be 
taken of the presence of steel in both faces to reduce 
the required thickness of concrete. Under combined 
bending and thrust the amount of tension steel is 
reduced because of the direct compression. The added 
compression does not stress the concrete as highly as 
might be expected since the reinforcement in the com- 
pression side takes part of the stress. Compression 
reinforcement is not very effective in thin sections, 
however. 

The depth of protective covering for reinforcement 
should be great enough to prevent rusting of steel or 
attack by chemicals in water. Good dense concrete is 
easily obtained, but conservative practice calls for 
2 in. clear of concrete cover over reinforcement. For 
routine computation, 214 in. is taken as the depth from 
face of concrete to centerline of adjacent layer of 
reinforcement. The concrete cover may be reduced to 
114 in. clear in top slabs if there is no fill above the 
culvert. 

Longitudinal steel requirements depend on the ex- 
posure to climatic conditions, and on the action of the 
structure as a longitudinal beam. A total cross-sec- 
tional steel area equal to 0.2 per cent of the gross con- 
crete section is considered adequate for buried con- 
duits, and extra bars are added in the bottom slab if 
there is a definite possibility of settlement causing 
longitudinal beam action. 

The length of lap for splices is usually specified as 40 
bar diameters for low-strength concrete. For 3,000-lb. 
concrete the lap should be 30 bar diameters. When 
lapped bars are of different diameters, the larger size 
determines the lap. 


Construction Joints 


Construction joints are more than just details 
incident to the building of drainage structures. For 
even small culverts, the engineer should study the 
need for and location of construction joints before 
the design is finished. Reinforcement should be detailed 
with this in mind, to simplify the construction as much 
as possible. 

The volume of concrete that can be deposited in one 
continuous placement usually locates the joints. Since 
the walls are relatively thin they should be cast in 
short lifts because of difficult placing and chance of 
honeycomb. 

Horizontal joints near bases of walls should be 
located slightly above the floor level to permit easy 
cleaning and to provide a stub on which wall forms may 
grip. Structurally speaking, this location is better than 
at the floor level as it is in a region of lower shearing 
and flexural stresses. The joint may be of several types, 
a few of which are illustrated in Fig. 13. The most 


Fig. 13. Horizontal construction joints. 


common, (a), consists of a roughened horizontal sur- 
face. Keyed joints as (b), (c), (d) and (e) are used in 
thick sections to provide greater watertightness, and 
restraint against shearing forces. They are superior to 
type (a), but are difficult to form and keep clean under 
average field conditions. Joints should be perpendicular 
to adjacent faces of concrete sections, as in (d) and (e), 
for the same reason. In fact, horizontal joints are 
usually prohibited in circular conduits subject to high 
internal pressure. 

Leakage through horizontal construction joints is 
rarely caused by lack of bond or contact at the joint, 
but is more generally the result of a layer of porous, 
segregated concrete just below the joint. The surface 
at a joint should be swept clean with a stiff broom or 
wire brush to remove all laitance, and to provide a 
roughened surface with some aggregate left exposed. 
All loose particles and debris should be removed and 
the surface dampened just prior to casting of con- 
crete against the joint*. 

Vertical construction joints in large culverts are 
spaced according to limitations of casting and lengths 
of forms, with a maximum spacing of about 30 to 35 
ft. Longitudinal reinforcement is continuous through 
such joints, and metal water stops may be installed to 
prevent leakage. 


Expansion and Contraction Joints 


The advisability of dividing buried conduits into 
noncontinuous parts is debatable. Many engineers 
eliminate all joints in the culvert or conduit barrel 
proper, others provide joints only at points a few feet 
from the wing walls when the latter are cast integrally 
with the culvert. In cases of heavy embankment load- 
ing and unstable foundations, culverts are sometimes 
separated into short units, and metal or rubber strips 
used to allow differential settlement without leakage. 
This tends to eliminate longitudinal beam action in 
the culvert and the possibility of transverse cracks, but 
it may permit vertical movement in adjacent units 
great enough to rupture the joints and throw the 
culvert out of alignment. 

Expansion joints are often made watertight by 
installing crimped metal strips, usually 20-0z. copper, 
across the opening and embedding the legs in the 
concrete at each side. Where watertightness is especially 
important and large lateral or vertical displacements 
are probable, a more elaborate joint detail is needed. 

The United States Bureau of Reclamation has 
developed several types of rubber seal joints** that 
have proved very effective. The joints are of two 
general types, employing either a 6-in. premolded rub- 
ber section with bulb edges, or a 9-in. section having 
a hollow central bulb in addition. For joints over 1% in. 
wide, or where appreciable deformation is expected, 
the 9-in. section is specified. The edge bulbs are em- 
bedded in the concrete as shown in Fig. 14, and resist 
any tendency toward displacement. The central bulb 
is designed for. toughness and resistance to shear. 
Laboratory tests and field installations have demon- 
strated that the joints can be deformed several inches 
transversely or longitudinally without damage to the 
water stopt. The rubber is fairly resistant to exposure 
in light, and a long service life can be expected when 
used in buried conduits. 

Vertical expansion joints should be either butt joints 
with dowel bars across, or bell joints with all rein- 
forcement stopped. In the former case, the protruding 
bars should be covered first with a heavy coating of 
hot coal-tar pitch and then with a paper sleeve to 
prevent bond with the concrete subsequently placed. 
The bell ends of bell joints should be carefully cast to 
insure uniform bearing without impairment of joint 
action. 

For average field conditions it is thought to be the 
best practice to use no expansion joints in the culvert 
barrel. 


*For full recommendations, see Concrete Information sheet 
Bonding Concrete or Plaster to Concrete, sent free in United States 
and Canada upon request to Portland Cement Association. 


**Tyevelopment of Articulation for Large Concrete Canal Struc- 
tures” by H. G. Curtis, Western Construction News, May, 1940. 


tThe rubber must have a tensile strength of at least 3,800 lb. 
per sq.in. and an elastic deformation of 650 per cent. 


25 


a mie), 1% : 
ae ah 


ae Zak 
(a) CROSS SECTIONS OF RUBBER WATER STOPS 


Concrete 


6" Rubber 
water stop 


s"Rubber filler, 
coat with bitum. 


material before @ 
installation 


(b) JOINTS FOR COVERED TOP SLABS 


2"Bituminous _I" 9" Rubber 
material — >| ae water stop 
Dehydrated = Sea ca ne) 


cork filler —— 4p .0 


I" Rubber filler 


x 
Nail required where 
bell is omitted 
Pade spain pcs Sl 
Paint contact surface 
with hot tar or asphalt 
(c) TYPES OF BELL JOINTS FOR SIDEWALLS 
AND BASE SLABS , 
(G" Water stop for joints not wider than’) 


Fig. 14. Rubber water stops. 


Unit Stresses Suggested for Design 


It has been the custom to use very conservative 
working stresses for culvert design because of un- 
certainties in load and use of approximate methods 
of analysis. Modern procedures of load determination, 
better methods of analysis, and concrete of high 
strength even under average field conditions all com- 
bine now to produce factors of safety far greater than 
those formerly obtained by use of low allowable stresses 
alone. It is entirely reasonable, therefore, to use allow- 
able stresses more in line with present conditions. 


The following allowable unit stresses have been used 
here for all typical designs. 


Allowable tensile stress in rein- 


forcémeiti, fe soe fs = 18,000 p.s.i.* 
Ultimate compressive stress in 

concrete (28 days)........... ff’, = 3,000 p.s.i. 
Extreme fiber stress in compres- 

BIOD Pee es ae fe = 1,200 p.s.i. 
Unit shear in members having 

end anchorage of bars, but 

without web reinforcement... v = 90 p.s.i. 


26 


Unit shear in members having 
end anchorage and web tein- 
forcement Nein A ee v 
(All shear to be taken by web 
reinforcement) 


Unit bond, deformed bars, ordi- 
Lary AUChOrage...ae eee u= 


360 p.s.i. 


150 p.s.i. 


Unit bond, deformed bars, special 
anchorages: 20, Sate ne eee u 


I 


C25 eas 
Design Constants: 


For balanced design, j = 0.867; k = 0.400; p = 
0.0133; kK = 208. 


Method of Designing Sections 


After determining maximum moments, thrusts and 
shears at critical culvert sections, the thickness of con- 
crete and the steel requirements may be computed by 
methods given in textbooks on reinforced concrete 
design. Culvert design, however, is usually concerned 
with bending moment combined with axial thrust on 
unsymmetrically reinforced sections. Standard equa- 
tions covering this case are unwieldy and not conducive 
to rapid design. It is worth while to use time-saving 
design charts and tables. 


Fig. 15 has been prepared to facilitate the design of 
sections subject to bending moment with or without 
axial thrust. It is general in that it covers cases of no 
compression reinforcement or of any desired amount, 
but it assumes only the usual design condition—tension 
on part of section. The chart will now be explained 
through comparison with standard design formulas. 


(1) For simple bending, no compression reinforce- 
ment, balanced design (concrete and steel stressed 
to allowable): 


; 12M 

d (in.) == ou 
; 12M 

Ag (sq.in.) = — 
s (sq.in.) f, jd 


in which M is the moment in foot pounds and 
other factors are as in texts and handbooks**. 


(2) For simple bending, compression reinforcement, 
balanced design: 


‘ 12M 
d is less than | Te 


_ 12M 
Agee: 
: 12M — Kbd? tales 
A',= 7 
a0 
n—l d ah! 
ape lick (1-5) 4 


*p.s.1.—pounds per square inch. 


**See Reinforced Concrete Design Handbook of the American 
Concrete Institute. 


He 


I 
| 


\y 
G 
\ 

N 

\ 

f 


a 
> 


SIMPLE MOMENT (M) OR EQUIVALENT MOMENT (Ms), IN rOOT KIPS 


CHART CONSTANTS 

f= 18,000 p.si. f¢=3,000psi. 

f= 1200p.s.i.(max. n=!0 
DESIGN CONDITIONS COVERED :- 


I Sections having moment, M, 
(ft.kips) with or without com- 
pression steel, As 

aes 


Il Sections haying moment, M, 
(ft. kips) combined with axial 
Thrust, N,(kips) with or without 

compression steel, As 


12" =i 


Bending and compression thrust: 
Ms (Ft-kips) = M + No" 
As=chart value. As= A-% 


Bending and tension thrust: 
Ms (ft. Kips) = M- 8g" 
As=chart value. As=At+# 


OEE 


| 


| 


100 


SIMPLE MOMENT (M) OR EQUIVALENT MOMENT (M 


Fig. 15. Design chart for sections 12 in. wide. For simple bending or bending combined with either axial com- 


pression thrust or tension. 


27 


(3) For bending combined with axial load it is ad- 
vantageous to express the equations in terms of 
an equivalent moment acting about the centroid 


Fig. 16. 


of the tensile steel. This equivalent moment repre- 
sents the combined action of M and axial thrust, 
N, and is termed M,. From Fig. 16 (a) it is seen 
that for compression thrust, 


ld 


d 
Ms; (ft.lb.) = M + DP N (lb.) 


For the case of tension thrust, Fig. 16 (b), 
d’ 
M, (ft.lb.) = M — 1D N (lb.) 


For combined bending, no compression reinforce- 
ment, balanced design, the modified equations 


are: 
12M, 
i- V5 
12M 
A, = fe a — 7, , for compression thrust, N 
12M N 
A; = = + — | for tension thrust, N 


fsjd s 


(4) For combined bending, compression reinforce- 
ment, balanced design: 


12M, 
Kb 


As has the same equations as in (3), and 
12M, — Kbd? 
d’ 
n—-1 ee d 1 d’ 1 
ite are 
The above equations are expressed in about the 
simplest general form, but still do not permit quick 


28 


d is less than / 


design. In the preparation of short-cut design charts, 
one may take advantage of the fact that for balanced 
design—that is, tension reinforcement and extreme 
concrete fibers stressed to the allowable—the variables 
fs, K, k, and n are constants, the values of which 
depend on the allowable unit stresses. j is not a con- 
stant as it varies according to amount and position of 
compression steel. Where concrete is not stressed to 
the allowable it varies with the concrete stresses. The 
precise values of j are used in Fig. 15 and more accurate 
steel areas will result than from use of an arbitrary 
J-value. 

The chart has two zones—the left covers cases where 
compression reinforcement is required, and the right 
covers cases where the maximum concrete stress may 
be anything from 1,200 p.s.i. (at A’; = 0) down to about 
700 p.s.i. at the right margin. 


For example, consider a 12-in. wide section of effec- 
tive depth d = 11 in., subjected to a simple bending 
moment, M = 30,000 ft.lb. Locate the moment 30 
ft.kips (equal to 30,000 ft.lb.) on the left margin and 
proceed horizontally to the right, to intersection with 
the solid diagonal line representing d = 11 in. The 
intersection is in the zone where compression steel is 
required, and the amount, A’, = 1.5 sq.in., is noted 
on the nearly vertical dotted line. The tensile steel area, 
As = 2.13 sq.in. (As = A for simple bending), is also 
found at the same point by interpolating between 
values of 2.25 and 2.00 on the sloping dotted lines 
representing A. 

If the effective depth of the section had been 12 in. 
instead of 11, the intersection of M = 30 ft.kips and 

= 12 in. is farther to the right in the diagram, at a 
point where A’, = 0 and A, = 1.92. In this case, in- 
creasing the effective depth of section from 11 in. to 
12 in. has produced a saving of 1.50 sq.in. of com- 
pression steel and 0.21 sq.in. of tension steel, per foot 
of width. 


Had the effective depth been 13 in., the maximum 


Revealed in the flood wake. A cloudburst near Tehachapi, 
Calif., washed out the railroad track and fill, leaving a 
locomotive beside the undamaged culvert. 


concrete stress would, of course, have been less than 
the allowable 1,200 p.s.i. As equals 1.76 sq.in. based on 
a changed value of j. 

Cases of bending combined with axial thrust are also 
handled simply by the chart. The first step is to de- 
termine the equivalent moment, M,, about the tensile 


steel. From (3), M@; = M = “ ; 
used for compression thrust and the minus sign for 
tension thrust. Next, locate the value of M, (ft.kips) 
on the chart and proceed horizontally to the inter- 
section with the solid diagonal line representing the 
effective depth, d. Read the value of A’, and A. To 
find A;, the A-value must be modified to include the 
effect of direct thrust: 


the plus sign being 


; N 
For compression thrust subtract = 
JS 


N 
For tension thrust add iz 
s 


For example, assume a 12-in. wide section having a 
total thickness of 11 in. and steel coverage of 2.5 in., 
acted upon by a moment of 14,000 ft.lb. and a direct 
compression thrust of 8,000 lb. 


11 
d = 11 — 2.5 = 8.5 in. di = — 2.5 = 3 in. 


M = 14,000 ft.lb. N = 8,000 lb. (compr.) 


00 
ae > = 16,000 ft.lb. 


From Fig. 15, for M,; = 16 andd = 8.5: 
A’, = 0.70 sq.in. A = 1.46 sq.in. 


M, = 14,000 + 


N 8 
A; =A —7= 1.46 — 18 = 1.02 sq.in. 


fs 8 
If the 8,000-lb. thrust were a tension thrust, the 
example would be solved as follows: 


11 
d@ =11 — 2.5 = 8.5in. d” => — 2.5 = 3in. 
M = 14,000 ft. lb. N = 8,000 lb. (tension) 


M, = 14,000 — a = 12,000 ft.lb. 
From Fig. 15, for M, = 12 ft.kips and d = 8.5 in.: 
A’, =0 A = 1.07 sq.in. 


8 
A; =1.07 + 8 = Pa sqain 


After becoming familiar with Fig. 15 the designer can 
tell at a glance the effect of changes in concrete stress 
and reinforcement with changes in effective depth of 
section, not only for simple bending but for bending 
combined with axial thrust. This visual relationship is 
also useful in cases where reinforcement of an arbitrary 
amount must be carried through sections of changing 
thickness. Moment and thrust requirements for a 
section are satisfied by a smaller depth by considering 
the effect of the available compression reinforcement. 


Typical Designs 


In the following section, the design of different 
types of culverts and conduits is explained, with illus- 
trative examples included. Typical designs are also 
given for transverse sections of the various structures. 
Required concrete thicknesses, dimensions and rein- 
forcement areas are tabulated for moderate ranges of 
sizes and load conditions. 

The designer may use the typical designs in a variety 
of ways. Where field conditions and loads are those 
assumed in the designs, suitable sections may be 
picked from the tables directly. If some load condi- 
tions are different, the tabulated designs may be used 
as a basis at least for final designs. Frequently, too, 
alternate culvert types are considered for a location. 
The tables permit a quick, intelligent comparison of 
types and facilitate the making of cost estimates. 

Since loads cannot be determined precisely and do 
vary from time to time during the service life of struc- 
tures, no special attempt was made in preparation of 
the typical designs to reduce quantities and thicknesses 
to the bare minima. Such action could be justified only 
in rare cases where all loads are known constants. 

Fundamental data* used in the tabulated designs are 
as follows: 


Truck Loads: 


10-ton** truck loads, plus impact, on exposed 
culvert slabs. 

10-ton** truck loads, plus impact, on buried cul- 
verts. (Effect ignored for fills more than 9 ft. thick 
above culvert.) 


Embankment Loads: 

Vertical pressures uniformly distributed on top of 
culvert, and unit weight of 100 lb. per cu.ft. of fill 
material (Case II, page 17). 

Lateral pressures at any point equal to one-third 
the vertical downward pressure at the point (see 
page 19). 


Hydrostatic Pressures: 

Pressures from water inside culvert to top, with 
no hydrostatic head above that point. 

Outside lateral hydrostatic pressures in excess of 
lateral earth pressures not considered. 


Load Combinations: 

Structures considered full of water or empty, 
depending on which causes the most severe design 
condition at a particular point. Other loads assumed 
to be acting. 


Allowable Unit Slresses: 
Allowable stresses given on page 26. 


*See “Design Loads and Procedures’, page 22, for general 
discussion. 


**For cases where 15-ton trucks are used, see Fig. 6, page 14, 
and footnotes to tabulated designs. 


29 


SECTION II—ANALYSIS AND DESIGN OF SECTIONS 


Square One-Cell Culverts 


Moment, thrust and shear coefficients for various 
load cases have been computed by moment distribu- 
tion* and are tabulated in Table III for the convenience 
of the designer. Reference is made to the “Design 
Loads and Procedures’, page 22, for detailed explana- 
tion of the loads. 

The quantity at the head of each column in Table 
III contains the general terms representing dimensions 
of the culvert and the specific load considered. Factors 
listed below are each to be multiplied by this quantity 
to give the numerical values of moment, thrust, or 
shear at each section. The location of the sections and 
the interpretation of the signs are given above the 
table. It is suggested that all dimensions be taken in 
feet and all loads in pounds so that numerical values of 
coefficients will be in the same units for all load cases. 


Part of Table III is condensed and simplified in 
Table IV, permitting the quicker computation of design 
coefficients at critical sections. Only Sections 4, 5, 6 
and 7 are included, the purpose being to use the results 
for the top slab and right wall as well. Some approxi- 
mation has been made in adjusting moments to faces 
of supports in Table IV. For instance, the factor, 


a E a | of the vertical load moment at Section 6, 


*Explained and illustrated by examples in Concrete Information 
sheets, Moment Distribution Applied to Continuous Concrete Struc- 
tures; One-Story Concrete Frames Analyzed by.Moment Distri- 
bution; Gabled Concrete Roof Frames Analyzed by Moment Dis- 
tribution; and in Handbook of Frame Constants. Free in the 
United States and Canada on request to the Portland Cement 
Association. 


TABLE III. Square Culverts 


Coefficients for Moment, M, Thrust, N, and Shear, V, in Transverse Sections 1 Ft. Wide 


Fig. 17. Transverse section. 


I II 


Uniform 


vertical load Culvert weight 


3.13¢(L+t)2 | t(L+t) 


5 | jelelle 
L+t : L+t 


L-5t L-4.1t 
BET ¢ ] ~.50 |-7 Ta ] 
+2 +11 


SIGNS 
+ Moment, M, indicates tension on inside face. 
+ Thrust, NV, indicates compression on section. 


+ Shear, V, indicates that the summation of forces at the left of the 
section acts outward when viewed from within. 


UNITS 


Moments in ft.lb; thrusts and shears in lb. 
(For P, w and T in lb.; L and ¢ in ft.) 


Ill IV v. 


Uniform 
lateral load 


Pressure from 
contained water 


M 


1.17L2(L+t) .0417w(L+t)2| w(L+t) 


+1.22 —21.3 


+1.22 “213 


.0188T(L+t)3 


Triangular 
lateral load 


eeae 
T(L+t)2 


Table III, has been condensed by assuming that the 
width, ¢, of support equals one-twelfth the span, Lf. 
All stresses are computed for transverse elements 1 ft. 
wide. 


TABLE IV. Coefficients for Moment, M, Thrust, N, and 
Shear, V, at Critical Sections of Square Culverts 


me Sections 
Load conditions 


M coeff. (algebraic part) 
N and V coeff. (algebraic part) 


I. Uniform vertical load 
P (L+t) 
P 


II. Culvert weight 
t(L+t)2 
t(L+t) 


III. Pressure from cont. water 
L2 (L+t) +0.63 
IV. Uniform lateral load 
w (L+t)2 —0.022 
V. Triangular lateral load 


T (L+t)3 -0.010 


Load conditions 
Moment, M 


Thrust, VV, or shear, V 
ft-l ben leeLb: 


I. Uniform vertical load 


WN or Vi 


-1900 
+2940 +2940 
II. Culvert weight 

M: 


W or V: 


III. Press. from cont. water 


IV. Uniform lateral load 
M: 


V. Triangular lateral load 
M: 


Total M**; 
Total N or V: 
Na” 
12% 

Nd” 
Ms=M+>,: 


A (Fig. 15): 
N (ib.). 

~ 18,000° 

A, (sq.in.): 


*Since pressure from contained water reduces the moment at Sections 5 and 6, 
the culvert is considered empty in design of these two sections. 

**The sign of M is ignored in further computations after the tension side of the 
section is noted. 


Example: Design of Section of Square Culvert 
Assumed data: Waterway opening = 48 sq.ft. 


Truck loading = 10-ton truck on 
unsurfaced secondary highway 
Fill on top of culvert = 5 ft. 
Averagefillpressures (CaseII, page17) 
Recommended design stresses given 
on page 26 
For an opening of 48 sq.ft., a square 
culvert would require a clear span, L, of 
approximately 7 ft. (7 X 7 = 49). Esti- 
mate ¢ equal to 8 in. 
Load factors for use in Table IV: 


Outside width of culvert = 7+2x 1p 


= 8.33 ft. 


Live load from 10-ton truck, Fig. 6, 
251.10 Ib: 

Dead load from fill, Case IT, 
= 5 X 100 X 8.33 = 4,170 lb. 


Uniform vertical load, P, lb. per lin.ft. 
= 5,880 lb. 
Uniform lateral load: 
5 x 100 
5100 64 
Triangular lateral load, equivalent 
fluid pressure: 


w, lb. per sq.ft. = 


100 
T, lb. per ft. of height = 5 ce 33 
Dimensions: L = 7 ft. t = 0.67 ft. 


Computations can now be made by 
reference to Table IV, and it is convenient 
to tabulate quantities on a computation 
schedule of similar form, as shown at left. 
The algebraic part of all coefficients on a 
horizontal line is computed first and then 
the numerical parts are used as multi- 
pliers, allowing one to compute and tabu- 
late values quickly across the schedule. 
This has been done at left for the first five 
load cases described on page 23. For 
instance, in calculating uniform vertical 
load moments by Table IV, the quantity 
P (L +2) = 5,880 (7 + 0.67) = 45,100. 
The multipliers at Sections 4, 5, 6 and 7 
are respectively — 0.042, — 0.042, — 0.022 
and + 0.083 (reading horizontally across 
the table) and the computed moments are: 
are: — 1,900, — 1,900, — 990 and + 3,740. 

If tis considerably larger than one-twelfth the 
span, substitution of the actual value of ¢ in the 
factors in the body of Table III may give un- 
reasonable results at some sections. In such cases, 
satisfactory accuracy for design may still be 
obtained by use of the coefficients in Table IV 
because the percentage of error will be small 


when several moments are combined to give the 
total moment on a section. 


31 


These values are recorded in the schedule as shown. 
Final moments, M; thrusts, V; and shears, V, are 
found by algebraically summing the quantities of each 
column. The next step is to check the shear and bond 
at Section 6. 
Since t = 8 in., d= 5.5 in. (assuming 2.5 in. from 
face to centerline of steel) 


eed 2 NE 
nits LON rr 2x %xX55 = p.s.1 
V 4,100 : 
Bonds20. = 5 = saa 


In the lower part of the schedule the required tension 
reinforcement is computed. The procedure follows that 
given in “Method of Designing Sections’, page 26, 
involving the use of Fig. 15. 

Points 4 and 5 have bending combined with axial 
thrust, so the equivalent moment, 
My, is first computed as 

M, (ft.lb.) = M + A 
1 py 
In Fig. 15 the moments are given 


without signs, so the sign of the final 
moment, MM, in the schedule is ignored 


Water- 
way 
opening 
sq.ft. 


1-in. round bars at 5-in. centers = 0.48 sq.in. 
Lo = 3.8 in. 

“B” bars are more than adequate for Points 4 and 5. 
Half of these bars may be stopped short of the lap at 
mid-height of walls. 

Volume of concrete = 4t(L + 2) 
= 4 X 0.67 (7 + 0.67) 
= 20.5 cu.ft. per foot 
Longitudinal reinforcement = 0.002 times gross area 
= 0.002 K 12 X 8 
= 0.19 sq.in. per foot 


Use 14-in. square bars at 16-in. centers = 0.19 sq.in. 


Typical Designs 


Table V gives dimensions, reinforcement, and con- 
crete quantities for square culverts. Average condi- 
tions as outlined in ‘““T'ypical Designs”, page 29, are 


TABLE V. Typical Designs of Square Culverts 


Longitudinal 
reinforcement 


SC bars 


size-spacing 


Transverse 


: Volume 
reinforcement of 


concrete 
cu.ft. per 
lin. ft. f 


Daebans 


size-spacing 


*“*A”” bars 
size-spacing 


after the tension side of the section is 
noted. 


The required steel area, As, per 
linear foot of culvert is computed by 
use of Fig. 15 and the reinforcement 
is arranged as in Fig. 18. 


"A" Bars 


yh | S 
NO Ns | WO Us 


i) 


—s 


la Clear for exposed ei 
top slabs, 2“otherwis 
E 


2"Clear (Place bars 


T 


ee © 


in center of 5'walls 
only) = 
Laps optional for 
small culverts 


— 


Construction joint 


ES 


ies 


Fig. 18. Typical cross section. 


=) alll seed S So 
++ NS N++ NS ++ NS ++ NS ++ 


— 


For Point 7, ‘‘A” bars must have 
an area of 0.67 sq.in. 


5g-in. round bars at 514-in. centers 
= 1.68 sq.in. 


For Point 6, ““B”’ bars must provide 
an area of 0.30 sq.in. and must have a 
total perimeter, Zo, of 3.8 in. per lin.ft. 


32 


NS N++ aon 


XX 


Net eet 
SEENON 
RS 
ENS tet et fe es es ; 
NINOS SDAON CwWOMW NYNANNwW NW SOOo SONNY PAB 
MNOWN WWHO CWNO BWHBRO WOOD NSCOCO WoNno oo5o5 


i 


ee 
tN 


non ANNAN ANnaoa NANA NOoLun PS 
RXRX 
— 


6 
5 
) 
B) 
6 
5 
6 
i 
6 
6 
6 
7 
6 
6 
7 
y 
6 
7 
8 
0 
6 
8 
9 
il 


WOOD 
ee 
NNhNre 


WOOwowo wwowd NANA ANNAN nonin Ph bb wwwww Lo oe Ow) 
— 


aAnann nono ann ANNAN 


os 
Ww hd bo When 


*Make “B” bars continuous across slabs for 2-ft. and 3-ft. spans. 
***°A”’ and ‘‘B’’ bars combined into one bar for walls of {=5 in. 
}Fillet quantities not included. 
tApplies also to H-15 loading plus impact, if t is increased to 71 in. and reinforcement 
is increased by 10 per cent. 


assumed in the designs. Before any culvert section is 
taken from the table, the engineer should become 
familiar with these basic conditions. 

Culvert spans range from 2 ft. to 9 ft., and load 
cases vary from those of exposed top slabs to 15 ft. 
embankment cover. One design is given for each incre- 
ment of embankment depth in the latter case. 

Fig. 18 shows the layout and arrangement of rein- 
forcement given in Table V. 


Rectangular One-Cell Culverts 


In changing from a square culvert to one having a 
rectangular section, the slab thickness increases rapidly 
as the spans become longer. The most economical ratio 
of slab thickness to wall thickness varies with the 
loads, spans and allowable design stresses, but it is 
convenient to determine economic relations for average 
conditions and to use them as constants within moderate 
limits. 

Various ratios of clear span to clear height are used in 


Old concrete box culvert under Beverly Blvd., Los Angeles, 


the field, a ratio of 1.5 to 1 being perhaps more common rome 

than any other. Table VI gives design coefficients at ; 

critical sections for culverts having clear spans one and Live load from 10-ton truck, Fig. 6, = Una 
one-half times the clear height. Dead load from fill, Case II, 

Slab thicknesses are taken as one and one-half times = 5 X 100 X 10.17 = 5,090 
the thicknesses of side walls, for buried culverts. In Uniform vertical load, P, lb. per lin.ft. = 6,800 
other respects Table VI is like Table IV 
for square culverts and is used in the é 
same way. Points of critical stress are at TABLE VI. Coefficients for Moment, M, Thrust, N, and 
mid-span of bottom slab (Point 7) and Shear, V, at Critical Sections of Rectangular Culverts 


at slab supports (Point 6). It will be 


found that the thin wall sections are SIGNS 
rarely critical for the spans and loads + Moment, M, indicates tension on in- 
considered. Siac lace ie ‘ 
+ Thrust, NV, indicates compression on 
section. 


Example: Design of Section 


+ Shear, V, indicates that the summatio 
of Rectangular Culvert 2 


of forces at the left of the section acts 
outward when viewed from within. 


UNITS 
Moments in ft.lb.; thrusts and shears 
in lb. 


Assumed data: 
Waterway opening = 52 sq.ft. 
Truck loading = 10-ton truck on un- 


surfaced secondary highway. Fig. 19. Transverse section. (For P, w and T in lb.; L and ¢ in ft.) 
Fill on top of culvert = 5 ft. 9 a 
Average fill pressures (Case IT, page Load conditions — 
17) M coeff. (algebraic part) 4 5) 6 ff 
F : N and V coeff. (algebraic part) a, 
Recommended design stresses given te ee ‘ M | ND) eee an ee Lon ae, 
on page 26. I. Uniform vertical load 
For an opening of 52 sq.ft., arectangular (1.5L+2) -0.025 an -0.025 pe -0.012 bore +0.100 
culvert having a span-height ratio of 1.5 ; 
to 1 would require, approximately, a clear II. Culvert weight 
height, L, of 6 ft. and a clear span of 9 ft. t (1.5L+t)? -8.4 a =13.4 os 6 cn +41.5 
(6X 9 = 54.0 sq.ft.) Ae! : ; F 
‘ : ‘ Ill. P f t. wat 
Estimate ¢ equal to 7 in. (Slab thickness vee PAG Neel ecoina +0.87 +2.05 +2.05 
equals 1.5 & 7 = 10.5 in.) 
: . Uni ] 1 load 
Load factors for use in Table VI: , i Say epee 40.067 -0.030 0.058 0.058 
Outside width of culvert = 9+ 2 X Pp V. Triangular lateral load 
= 10.17 ft T (L+1.5t)3 +0.034 —0.016 —0.033 —0.033 


33 


Uniform lateral load: 
> X 100 
3 
Triangular lateral load, equivalent fluid 
pressure: 


100 
T, lb. per ft. of height = mor 33 


Dimensions: L = 6 ft. t = 0.58 ft. 
15L+¢=9.58ft. D+ 1.5¢ = 6.87 ft. 


Computations based on the constants are 
given in the schedule at the right. 


w, lb. per sq.ft. = = 167 


In computing steel areas required for the 


Computation Schedule for 9x6-Ft. Culvert 


Sections 


Load conditions 5 
Moment, M 


Thrust, NV, or Shear, V M 
; ttslbaileel bee iettsibs 


I. Uniform vertical load 


: 630 — 780 
INET a ae +3400 +3400 
II. Culvert weight 

M: 


N or V: +1220 


III. Press. from cont. water 


critical sections, note that 


wall depth, dw = 7 — 2.5 = 4.5 in., and 
slab depth, ds = 10.5 — 2.5 = 8 in. 


Note, also, that only a small amount of ten- 
sile reinforcement is necessary at Points 4, 
5 and 6. This is indicated by the fact that 
some required steel areas fall outside of Fig. : 
15. When this happens, double the value of oS 
M,, take the chart value of A and then divide / 
it by 2, for approximate results. 


Checking shear and bond at Point 6, 


IV. Uniform lateral load 
M: 


V. Triangular lateral load 
M: 


Total M**: 
Total NV or V: 


Na" 


M;=M+ 12° 


+4620 


A (Fig. 15): 


ee ee 102 mene 
Sreyiee ier ien 
V 4,620 


Fig. 20 gives the suggested arrangement 
of reinforcement for rectangular culverts. In 
this example “A” bars must have an area 
of 0.80 sq.in. per foot. 34-in. round bars at 614-in. 
centers give 0.81 sq.in. “B” bars are controlled by 
required perimeter of 2.9 in. %-in. round bars at 
614-in. centers give 0.37 sq.in. and Zo = 2.9 in. 


(Og Bars "A" Bars 


oy ee 


Men rapes or 
ieee 2"clear otherwise 
pas LSL 
772"Clear for walls over S"thick. 
4 For d'or 5"walls place bars at 

HL el center of wall 


pa] 


Laps optional for 


Symmetrical 
small culverts 


¥ about ¢ 


Construction joint 


'C’ Longitudinal bars Ao 


SOA Soo ei A aee er 


; “ ” : 7 a ae ! 
A Bars “B’Bars- 1 
Fig. 20. Typical cross section. 


34 


_N (b.), 
18,000° 
As (sq.in.): 


*Since pressure from contained water reduces the moment at Sections 5 and 6, 
the culvert is considered empty in the design of these two sections. 

**The sign of M is ignored in further computations after the tension side of the 
section is noted. 


Volume of concrete = 6 ¢t (1.083L + 2) 
= 6 X 0.58 (1.083 & 6 + 0.58) 
= 24.8 cu.ft. per foot 
Longitudinal reinforcement = 0.002 times gross area 
= 0.002 K 12 X 10.5 
= 0.25 sq.in. per foot 
“C”’ bars, 4-in. square at 12-in. centers = 0.25 sq.in. 


Typical Designs 

Table VII contains dimensions, reinforcement and 
concrete quantities for transverse sections of rectangular 
culverts. The designs are based on the average condi- 
tions outlined in “Typical Designs’, page 29, to which 
reference should be made. Table VII and Fig. 20 are 
used in the selection of sections in the same way as were 
Table V and Fig. 18 for square culverts. 


Fig. 21. Change in invert slab suggested for culverts having 
small dry-weather flows, to insure better self-cleaning 
velocities. Note that transverse reinforcement is placed 
advantageously to resist bending moment. 


TABLE VII. Typical Designs of Rectangular Culverts 


Dimensions Transverse reinforcement Longit. reinf. 


Waterway 

opening ee **A”’ bars ““B” bars “C” bars 
aa tt 7 Height | Thickness | Span | Thickness |  size-spacing size-spacing size-spacing 
in. ft.-in. in. 


* 


xX 


XX 


oth ya 
ea OU a 


CONMN DUAN UKAOMNMN ANDADAHR AnDAD BDnnnN 


ADDR COOSD ANDDHR SOSSD ADDR SOOO 


N TDOUOD OOOD ANND DARA 


AXA 


ANAND WANNA) NAAN ANNAN ANAND DANAAN 


etn 
SREECN 


NANNY ADAH UMMM PEER Wwww Baul 
SONIN ONND ADAH ADAD nUMMA 2p BaH 


SSSS PEGS ARPP AAMD PRER ~oeyy 


—_— 

—— 
Ue TE aie} 
WoollSE ala) 


*Make ‘‘B” bars continuous across slabs, for 3-ft. span only. 
**Fillet quantities not included. 
tApplies also to H-15 loading plus impact, if t is increased to 7)4 in. and reinforcement is increased by 10 per cent. 


Two-Cell Box Culverts 


Factors that govern the selection of two-cell box 
culverts have been discussed under the heading “‘Choice 
of Culvert Shape’, page 20. The first design step is to 


Marietta Highway near Atlanta, Ga. 


are satisfied by using square openings. 


A simple, yet efficient, two-cell culvert in Tarrant County, 5 : 
Texas. form for several points on the cross section of culverts 


Volume of 
concrete 
cu.ft. per 
lin.ft. ** 


ee 
PNN& BRR COSM MAND 


NOR ee 
HODH ANDO CHMMN NUNNSO HHH COoOoO 


PwWdOdy wWNydy-e 
NWOS NABH 


Box culvert of two 10x10-ft. cells under the Atlanta- 


decide on the shape of openings to give a required 
waterway area. Rectangular shaped openings may be 
advantageous in certain cases, but average conditions 


Table VIII contains design coefficients in algebraic 


35 


TABLE VIII. Box Culverts of Two Square Cells 
Coefficients for Moment, M, Thrust, N, and Shear, V, in Transverse Sections 1 Ft. Wide* 


6 


iP og 
seat 


Fig. 22. Transverse section. 


I 


II III 


SIGNS 


+ Moment, M, indicates tension on inside face. 
+ Thrust, NV, indicates compression on section. 


+ Shear, V, indicates that the summation of forces at the left of the 
section acts outward when viewed from within. 


UNITS 


Moments in ft.lb.; thrusts and shears in lb. 


(For P, w and T in lb.; L and ¢ in ft.) 


IV V 


Uniform 
vertical load 


M iN M 


Section 


Culvert weight 


Pressure from 
contained water 


Uniform Triangular 
lateral load lateral load 


Ney? mM |nwl|yV 


M N\V M’ | VSN 


.0139P(L+2) P t(L+t)2 


cual 
L+t 


+2 + 9.0 


a | 
L+t 


SVE | Is, - 


+.208 sa] 


t(L+t) L2(L+t) L 


0556w(L+t)2} w(L+t) | .01237(L+)3 | T(L+t)2 


—1.6t 
D+ 


t 


L-16.6t 
L+t 


| eo) O16 =O 


+0.38 =10 


| E60 +152 -10 


+0.50 : +.16 


—0.25 : ; +.16 


-l : +.16 


- 1.7 +1.52 


ae | see) 
L+t L+t 


= 7.3 —Zal +1.25 


Te Tack AS) as) 


L+t L+t 
L-6.5t L-7.3t 
-[ a —.208 |-12.9 Ta ] —210 +1.94 —21 


+2 +20.2 +0.49 -2] 


[-1.6t 
mS L+t 


] +.292 | -40.4 =| +160 0.97 -2] 
[+t 


*See footnote page 31. 


having two square cells, as shown TABLE IX. Coefficients for Moment, M, Thrust, N, and Shear, V, 


in the accompanying figure. The at Critical Sections of Culverts Having Two Square Cells 
coefficients of the most critical 
points are simplified and con- | yaa conditions posuons 
densed in Table IX, which is sug- M coeff. (algebraic part) 6 
gested for routine computations. Nand V coeff. (algebraic part) 

: ; M | Nt 
Reinforcement required at these pease De mt Ba 
points is to be used for other sym- I. Uniform vertical load 
metrically located points on the nue uM +0.208 0.000 (0 Oe ae +0.292 
cross section. Note that. wall and 

i II. Culvert weight 

slab thicknesses are made the same, MEAD Pie _4.7| 420.21 -34.2 
although a small saving in concrete t (L+t) +130 +210 
might result tfrom varying thes | |= <..08 ae 

5 III. Press. from cont. water 
thickness of concrete from exterior L2 (L+1) ~2.19 +1.94] +0.49| -0.97 
Loecenters walls sande fron Lops tOnmue ts eee eet ee 
bottom slabs. A constant thickness ae ret ane Fp: +0.069 0.056 |-0.014 |+0.028 
based on the most critical section ———— 
is suggested for average designs We Trengular lateral toad 


T (L+t)3 +0.035 0.031 |-0.008 |+0.016 | 


due to simplicity in construction 
and to the fact that any excess {Thrust on Section 6 equals numerically the shear on Section 7. 


36 


concrete at a noncritical section is Computation Schedule for Culvert Having Two 9x9-ft. Openings 
offset by a saving in reinforcement 


required at the section. Sections 
Load conditions 

Example: Design of Section of Moment, M i 
Culvert Thrust, NV, or Shear, V M 

. > sede, || seston, |) taal Dey, 

The design of a transverse section 
of a two-cell culvert is illustrated by I. ear vertical load bak bined Meee 
6a 5 : a bs is 

an example similar to those given for Niger 


one-cell culverts. 
II. Culvert weight 
M: 


Assumed data: : 
Nord: 


Waterway opening = 160 sq.ft. 


III. Press. from cont. water 


Truck loading = 10-ton truck on M: 
unsurfaced secondary highway 


Fill on top of culvert = 5 ft. 


Average fill pressures (Case II, V. Paty Su lateral load 
page 17) 8 


IV. Uniform lateral load 
M: 


Total Mt: 


Recommended design stresses Porat Ne ceie 


given on page 26. 


For an opening of 160 sq.ft., a cul- 
vert having two square openings would 
require a clear span, L, of approxi- 


mately 9 ft. (waterway = 2X9 X 9 A (Fig. 15): 
= 162 sqft.) _N (b.). 
Estimate ¢ equal to 9 in. (thickness of ee ): 
slabs and walls). ae see 
Load factors for use in Table LX: *Use also for shear, V, at Section 7. 
**Culvert assumed empty for design of Sections 6 and 7. 
Outside width of culvert {The sign of M is ignored in further computations after the tension side of the section 
=2X9+43X 0.75 = 20.25 ft. pe noted: 
Live load from 10-ton truck, Fig. 6, = 1,710 Transverse reinforcement: (See Fig. 23) 
Dead load from fill, Case IT, rie 
=5 x 100 X 20.25 = 10,130 Point 9: As = 0.86 sq.in. Zo = 3.6 in. 
Uniform vertical load, P, lb. per lin.ft. = 11,840 “A”? Bars: 
Uniform lateral load: 7%-in. round at 12 in. = 0.60 sq.in.; Zo = 2.8 in. 
5 X 100 “Be : 
w, lb. per sq.ft. = pe 167 e “eu : 
3 5g-in. round at 12 in. = 0.31 sq.in.; Do = 2.0 in. 
Triangular lateral load, equivalent fluid pressure: Total A, = 0.91 sq.in.; Zo = 4.8 in. 
100 : : 
T, lb. per ft. of height = c 33 Point 8: As = 0.53 sq.in. 
Dimensions:L = 9ft. {=0.75ft. L+t = 9.75 ft. “B” Bars: 7-in. round at 12 in.= 0.31 sq.in. 
Computations based on the constants are given in the “C” Bars: }4-in. square at 12 in.= 0.25 sq.in. 
schedule above. Total As = 0.56 sq.in. 


Unit shear at Point 9: : : : 
d = 9.0 — 2.5 = 6.5 in. Point 7: As = 0.33 sq.in. Zo = 3.1 in. 


4,620 “D” Bars: 


[ie [ois 4X 6.5 = 68 p.s.i. (90 allowable) Ys-in. round at 6 in. = 0.40 sq.in.; Zo = 3.1 in. 
Bond: “TD” bars are also satisfactory for Points 5 and 6. 
Point 9: Zo = eet 020. Sah =e}. 001 
oe DP Ne U5 SRW Oe oe tA small error is introduced by assuming the wheel load dis- 
4.000 tributed over both spans instead of one span taking more than 
Point 7: Xo = ? oe ane half. This is offset by designing the top slabs the same as the 
; D258 615 bottom slabs, since more severe conditions occur along the bottom. 


37 


Half of the ‘“‘D” bars may be stopped 
short of the lap at center of side walls. 


“\"Clear for exposed top 


Vertical ‘‘E’’ bars take negligible 


moment according to design assumptions fe 5 slabeietor ecwice 
for buried culverts, but should meet tem- HONE aaa! 
perature requirements, and the spacing fe : ae: Symmetrical 
should be consistent with slab steel spac- tH a about € 
i a 4\ one 41.31" E"Bars. Adjacent bars fx >: 
ing. ; dl Res ) D" Bars.Stop alfesnare Pde staggered Onstetne freee | 
“Fe” Bars: )4-in. round at 18 in. each ipa bars shortoflap + Mice ncr ae ee joints 5 
face, making 0.27 sq.in. total See | 
eS 3 Ont 4st] 'C" Bars(Alternate 
Ne 5 b : ae Chet PEAESe Dre x 
= 7 X 0.75(9 + 0.75) — 0.75? or ah ree 
= 50.6 cu.ft. per lin.ft. A’ Bars (Alternate with “B" bars) 


Fig. 23. Typical cross section. 
Longitudinal reinforcement 


= ().002 times gross area 


= 0.002 K 12x 9 Typical Designs 


= 0.22 sq.in. per foot of slab or wall Designs of transverse sections of two-cell culverts 


“Rh” Bars: based on average conditions of “Typical Designs’, 

Vf iaheruareiat 13 ime OOS serieer toot page 29, are given in Table X and are illustrated in 

a 2 ee ge Fig. 23. Load cases covered are as in preceding design 
Place as shown in Fig. 23. tabulations for other culvert types. 


TABLE X. Typical Designs of Two-Cell Culverts 


: Longitudinal 

Waterway pertn bis Transverse reinforcement fetta ge Volume of 
opening fone Sea 
sq.ft. ft L t *““A”’ bars ““B”’ bars “C” bars “D”’ bars “EK” bars “F” bars nee 

ra ; ft. | in. | size-spacing | size-spacing | size-spacing | size-spacing | size-spacing | size-spacing an 

Q** By 6 ote 12 le — 12 lye — 12 | 9 - 6 14S e= 12 lye - 13 19.0 

50 oso BY 6 Toe 28 ie 88 East = Ol ea = Eel) SS l4e — 16 19.0 

5.9-10 5) 8 Vitae ye — 8 34 —- 8 | % —- 4144) He —- 16 lye - 12 26.0 

10.5-15 5 ) UGA eS) Viasat) S4tt ea LG) (Ee oeP a4 34° — 16 Wye = 11 29.6 

Ot 6 6 ole we VS = 12 160 — 12 | 40 -6 go — 12 Yo =e 22.9 

72 1.5- 5 6 7 49 - 10 l4e - 10 34% — 10 34 — 5 346 — 20 4e — 14 26.5 

5.0-10 6 8 %e- ll be — Il 540 = 11 | 34059516.) 169) =" 22 Ye - 12 30.7 

10.5-15 6 | 10 546 = 10 oe 10 340 OS ee lor — 20 be Ni) 38.8 

Oe i 6 Woe) es MM po Fah 18 = 11°} wo =— Sle) Yo - 11 oe 26.0 

98 15-5 7 4 54 — 9 piek Ee) 34 —- 9 | % —- 4146] %e - 18 1 aaa 30.6 

9.9-10 7 9 54e - 9 54e - 9 og? =| OR t6o mean ye - 18 OE als 40.1 

10.5-15 ie et Z, 34% — 10 Poe 10) 130 LOO oCu— eo is AV 540 — 12 59.0 

On 8 6 ete La etn la ee = AL eee = olathe neg? an LL oe = hi) 29.5 

128 Loe 8 8 34¢ — 10 Poeun LO Vee 2100 tote BO 4g — 20 lye — 12 40.0 

9.0-10 8 | 10 yr — 14 34% — 14 ee CE eet Ye — 14 Vhs aa 90.8 

10.5-15 8 | 13 WE = NaN Dae soe 181 ye = URN es = BAe = ee ie eh 67.7 

ts 9 6 v9 10 $44 5= 710 a? 808 eee ee o10 Lon 9 33.0 

162 Lo= 5 9 ) ee — 12 BAe = 12 Bee AWA A Me ye 18 ei 50.6 

S 5.5-10 2D al ie - ll 546 — 1) We O-AIL |) ee 5 ied a 9 ge — 14 62.8 

10.5-15 9 | 14 len 13 eels See — 1a oe = 6 he Sal) ag = nt! 81.7 

Oe 10 6%) 3%4¢ - 13 34¢ -— 13 34 — 13 | ¢ — 64% | 34% — 13 546 - 1] 39.6 

200 15-5 10 ie = AlZ o49m ele Yoo 1D Bee 36 Ye - 18 ae as WP 99.9 

9.9-10 10.) 12 le = 12 24% — 12 Gd aD LG as, 6 54e — 24 Be — 12 76.0 

10.5-15 10 | 15 Leas i 4 ec b4o —*11 | Be - 5146 | 54% = 22 bE Moe AS 96.9 


*Fillet quantities not included. 
**Applies also to H-15 loading plus impact, if t is increased to 7)4 in. and reinforcement is increased by 10 per cent. 


38 


Three-cell box cul- 
vert on the Atlanta- 
Marietta Highway, 
Atlanta, Ga. Each 
opening is 8x8 ft. 
and wing walls are 


16 ft. long. 


Three-Cell Box Culverts a point where temperature stresses become significant. 


The economy gained through construction of one con- _—‘ Forces induced by expansion or contraction of one 
tinuous structure instead of several small independent part of the structure relative to another may usually 
culverts increases with the number of cells added, to —_ be ignored, however, due to the protection from tem- 


TABLE XI. Coefficients for Moment, M, Thrust, N, and Shear, V, at 
Critical Sections of Culverts Having Three Square Cells 


SIGNS 

+ Moment, M, indicates tension on inside 
face. 

+ Thrust, NV, indicates compression on 
section. 

+ Shear, V, indicates that the summation 
of forces at the left of the section acts 
outward when viewed from within. 


UNITS 
Moments in ft.lb.; thrusts and shears in lb. 


(For P, w and T in lb.; L and ¢ in ft.) 


Fig. 24. Transverse section. 


Sections 


Load conditions 
M coeff. (algebraic part) 
Nand V coeff. (algebraic part) 


I. Uniform vertical load 
P (Lit) , —0.005 |+0.020 |-0.026 —0.024 |+0.011 
0.19 


+0.14 


II. Culvert weight 
t (L+t)2 -8.0| +22.6| -26.2 


t (L+t) +168 


III. Press. from cont. water 
L2(L+t) —2.25 +1.86 | +0.66 | —0.54 —0.26 | —0.26 


IV. Uniform lateral load 
w (L+t)2 +0.072 —0.053 |-0.019 |+0.015 +0.008 |+0.008 


V. Triangular lateral load 
(L+t)3 +0.036 0.030 |-0.011 |+0.009 +0.004 |+0.004 


39 


perature changes afforded by the earth embankment. 
In the case of very wide culverts with top slab directly 
exposed it is advisable to cut the structure into two 
or more identical parts. In this way bending moments 
caused by unequal temperatures of different members 
are reduced, and the analysis of, say, one three-cell 
culvert used twice is simpler than the analysis of a 
six-cell culvert. 


The design of a multi-cell culvert cannot be stand- 
ardized to the same extent as were the types previously 
discussed. Some economy will result from closely adjust- 
ing the thickness or reinforcement of a section in line 
with the design stresses, which depend on particular 
load conditions. As a basis for design, however, the 
coefficients of Table XI are very useful. Required thick- 
ness of concrete at critical points may be quickly com- 
puted for the final analysis, and when a constant thick- 
ness is satisfactory for all members the final design itself 
may be made from the table. 


Modified Circular Culverts and Conduits 


Type I Culverts or Conduits 


Fig. 25 illustrates the circular conduit discussed in 
the section, “Choice of Culvert Shape”, page 20. The 
main disadvantage of this type is that it has been diffi- 
cult to design in the past. The cumbersome or empirical 
methods of analysis often used have not engendered 
confidence, and heavy, overly conservative structures 
have resulted. 


Culverts like that in Fig. 25 and those of other shapes 
required for special conditions can now be designed 
rapidly and accurately with a minimum of work and 
time by application of the method presented in the 


40 


Large three-cell cul- 
vert near Frederick, 
Okla. 


publication Analysis of Arches, Rigid Frames and Sewer 
Sections*. 


The standardized Type I section may be used eco- 
nomically for many kinds of covered conduits. Loads 
vary for these different structures but design studies 
have shown that the one cross section is satisfactory 
for a wide range of conditions. The change in required 
thickness of section from point to point to meet design 
conditions is close to that given in Fig. 25. Note that 


*Available free in United States and Canada upon request to 
Portland Cement Association. 


a” PROPERTIES OF SECTION 
Area of opening=3.14r? 
Area of concrete =3.21(r+t) 
HYDRAULIC VALUES: 


yeas radius =0.5r, 

Section flowing full) 

Max. hydraulic radius = 0. 
(Depth of flow=1.62r) 
(Water area= 2.73r?) 


(Ge Horizontal diameter : 


Reinforcement 
not shown 


\— 26°34! 
\ 
Vertical diameter 


0.618 (r+t) 


0.382 (r+t) 


Fig. 25. Cross section of Type I[ culvert or conduit. 


the shell thickness is the same at horizontal and vertical 
diameters. Design moments, thrusts and shears are 
not alike at these points but the critical stresses result- 
ing are not materially different. Adjustment in the 
amount of reinforcement at the various sections is all 
that is necessary if the basic thickness, ¢, is determined 
from the most severe combination of stresses. This 
usually occurs at centerline of invert or at the horizontal 
diameter. 

Adoption of the standard shape of Type I conduit 
has made it possible to determine the moments, thrusts 
and shears for the usual load cases and in terms of 
shell thickness, ¢, and radius, r. 

Table XII gives design moments, thrusts and shears 
at closely spaced points around the cross section. The 
locations of the points are given above the table. Tabu- 
lated coefficients are similar to those presented in pre- 
vious tables for box culverts, and are used in the same 
ways. ; ; . f 

Study of the coefficients will show that shear may rear ‘Hosviaburg, Pe. Note the substantial character, of 
be ignored in the usual case as thickness of concrete the forms essential for good construction. 


TABLE XII. Coefficients for Moment, M, Thrust, N, and Shear, V, in Type I Conduits 


Location of points SIGNS 


Angle at y Angle at + Moment, M, indicates tension on inside face. 
Point center with Point center with 
horizontal horizontal 


Crown +90.0° 


+ Thrust, NV, indicates compression on section. 


+ Shear, V, indicates that the summation of 
forces at the left of the section acts outward 
when viewed from within. 


UNITS 


Moments in ft.lb.; thrusts and shears in lb. 
(For P, w and T in lb.; h, r and ¢ in ft.) 


Fig. 26. Half section. 


I LV V VI 


Uniform 
vertical load 


M n\|yv Aon babel ue N 


Pressure from Uniform Triangular Hydrostatic 


Conduit weight contained water lateral load lateral load head * press. 


Section 


t. t t. 
P(r+5) r2(r+5) r2 : w(r+5) w(r+5) T(r+5)3 T(r+5)? T(r+5)? hr 


=39 EOI .00 | —.202 | +0.64 .00 = O2eS) 
—38 SOO) || alls) || HOS || HOKOs) || =O O25 
-36 +0.86 | —36 |—.153 | +0.59 | —24 Ole 
+0.63 | —.49 | —.068 | +0.49 | —.38 —62.5 


+.118 
+.116 
+.083 
+.027 


+ 
—a— 


+++ 


SE +0.37 | —.49 | +.041 | +0.34 | -.45 =—62.0 
=il8 +O oon \etaloOu cr Ouly |e 42 —62.5 
—14 HOLOY || allah || ce} || ONO) | = Xo =O2eo 

02005 | +201) 2807170200) 15 —62.5 


= 03i0 
—.093 
=p 112/5) 
SS 


INE SOCINIER pe Cocos) Coico 
OND NINO OW DAO ae Ne 


| 


| 


—— 


—13 SAO OME || ceed) |) Ser42} |) ONO) |) aaKOt O20 
—16 +0.06 | +.38 | +.250 | +0.05 | +.35 —62.5 
—42 +0.49 | +.39 | +.120 | +0.55 | +.43 -62.5 

+0.66 | +.42 | —.013 | +0.83 | +.53 O2e0 


— 


| 


+0.84 | +.35 |—.145 | +1.11 |] +.46 —62.5 
SOD || credit) |p eeeiih |) calbeya |) ea sdh7/ =O2n0 
+0.99 .00 | —.243 | +1.36 .00 —62.5 


+.071 
+.095 
Invert +.099 


++ 4 
eon 


*Head, A (ft.), measured up from inside face at crown. This pressure produces no appreciable moment or shear. Use VI only with III. 


41 


Large culvert on Pennsylvania Turnpike showing arch 
centering still in place. 


required for moment and thrust is more than adequate 
for shear. For unimportant designs, a considerable 
saving in time can also be made by carefully designing 
for stresses at three points only: centerline of invert, 
crown, and the horizontal diameter. Part 
of the tension steel required at each sec- 
tion is then extended just past the nearest 
point of inflection (point of zero moment). 
Note in Table XII that moments change 
sign between Sections 3 and 4 and also 
between Sections 9 and 10. Points of in- 
flection thus occur practically on diagonal 
45-deg. lines intersecting at the conduit 


Load conditions 
M coeff. (algebraic part) 
N coeff. (algebraic part) 


used in combination with IIT. The excess pressure is 
taken mainly by tension on all sections due to the 
approximately circular shape of the conduit. 

Condition VI is not important in culvert design, as 
most culverts are not designed for flow conditions pro- 
ducing much hydrostatic head. The condition is com- 
mon in design of storm drainage conduits, sewers and 
inverted siphons and has been included in Tables XII 
and XIII for that reason. 


In the design of large conduits of Type I, the required 
thickness, t, may be roughly computed by considering 
uniform vertical load coefficients alone. For this condi- 
tion the thrust is independent of ¢ and the moment is 
little influenced by an approximation of ¢. A tentative 
thickness is computed, adequate for the three critical 
sections under uniform vertical load, and this value of 
{ is used in summing up moments and thrusts due to 
all the load conditions. The resultant moment and 
thrust values are then used to check concrete stresses 
and steel requirements for the final design. 


Use of the coefficients will be illustrated by the design 
of a conduit section. 


TABLE XIII. Coefficients for Moment, M, and Thrust, N, at 


Critical Sections of Type I Conduits 


Sections 


Center 
of invert 


M N M N 


Horizontal 
diameter 


longitudinal axis, no matter what com- 
binations of load conditions I to VI are 
assumed. The fixed positions of the 
points of inflection are convenient in com- 


I. Uniform vertical load 


P (+5) 
IP 


puting points at which transverse rein- 
forcement may be stopped. A common 
rule is to stop the main tension reinforce- 
ment of one face at a distance of ten bar 
diameters past the near point of inflection. 


Table XIII gives the moment and thrust 
coefficients at the three critical sections 
in a more convenient form than in Table 


XII. 


The uniform vertical load, I, is more 0 
significant than other loads as it produces hr 
greater moments at critical sections than 
do any of the others. Load conditions II 


and III add to vertical load moments and ie ( 


conditions IV and V reduce them, as might 
be expected. Condition VI is internal 
hydrostatic pressure on the conduit due 
to an assumed free water level above the 
conduit crown. This pressure is in addi- 
tion to that caused by the conduit flowing 
full (condition III) and should only be 


42 


II. Conduit weight 


III. Press. from cont. water 


t 
2 a 
r (+5) 
72 


VI. Hydro. head pressure 


IV. Uniform lateral load 


t \’ 
ir 

Ww (+5) 
2 


V. Triangular lateral load 


Example: Design of Section of Type I Conduit 


Assumed data: 
Required waterway opening = 150 sq.ft. 
Truck loading = 10-ton truck on unsurfaced sec- 
ondary highway 
Depth of embankment over conduit = 10 ft. 
Average earth pressure conditions, namely: 
Weight of earth = 100 lb. per cu.ft. 
Vertical load, P, on conduit equals weight of 
earth prism above conduit (see Case IT, page 17) 
No hydrostatic head above crown (Load Condi- 
tion VI) 
Recommended design stresses given on page 26. 
For an opening of 150 sq.ft., the inside radius is 
150 
meas 14. 
Assume, tentatively, that { = 12 in.= 1 ft. and deter- 
mine moment and thrust at horizontal diameter, the 
critical section for thickness because of high compres- 
sive stresses in the concrete. Vertical load coefficients 
only are used to check the assumed thickness. 
Total verticalload, P* = (unit weight of earth) x (depth 
of cover) X (outside width of conduit) 
P=100 X10 X 2(7 +1) = 16,000 lb. 
From Table XIII, for uniform vertical 
load at horizontal diameter: 


= — 0.125 P (- +5) 


= — 0.125 x 16,000 (7 + 0.5) 
= — 15,000 ft.lb. (tension at out- 


side face) 
N = + 0.500 P = + 0.500 X 16,000 


r =sE(eO Ie Ge say dhl: 


Load conditions 
Moment, M 
Thrust, V 


View of a completed culvert on the Pennsylvania Turnpike. 


The computation schedule has the same form as 
Table XIII and permits the insertion of numerical 
values directly. 


*Live load due to 10-ton truck plus impact is negligible in 
comparison to earth pressure for 10-ft. cover, and is ignored. 


Computation Schedule for Type I Conduit. r=7 Ft. 


Sections 


Center 
of invert 


Horizontal 
diameter 


M N M N 
ft.lb. lb. ft.lb. lb. 


= + 8,000 Ib. (compr.) 


Nd" 12 : 
M,=M+—,, (a= 2-25-3510.) N: 
8,000 3.5 


=15,000+ 12 = 17,300 ft. lb. 


From Fig. 15, for M,= 17.3 ft.kips, it 
is seen that the required effective depth 
is slightly less than 9.5 in. if no compres- 
sion reinforcement is desired. 

t= 954 2:5 = 12 in. 

By use of Table XIII, compute resul- 
tant moments and thrusts at crown, hori- 
zontal diameter and invert, based on 
{ = 12 in. for all loads. 


Numerical values of factors: 
r=7ft. t=1 ft. (“+5) ==: 7.5 it; 
P= 100 X 10 X 2(7 +1) = 16,000 lb. 


IV. Uniform lateral load 
M: 


I. Uniform vertical load 


II. Conduit weight 
M: 
N: 


III. Press. from cont. water 


N: 


N: 


V. Triangular lateral load 
M: 


N: 


Total M: 
Total NV: 

vile ping pls 
d =5 72,553.95 12° 


Nd" 
Ms=M+>5 ° 


A (Fig. 15): 
N (lb.) , 

~ 18,000" 

As (sq.in.): 


—4,550 


—2,810 


+14,040 


450 
14,490 
Lae 


—0.09 
1.07 


—15,000 


—4,140 


—5,440 
SOLO 


+4,960 
+2,520 


+3,900 
+1,190 


—15,720 
+1,530 


2,650 
18,370 
1.49 


—0.50 
0.99 


+11,880 
+8,000 


+3,770 
+1,770 


+4,780 


+4,080 


—3,380 
0 


+12,970 
+9,080 


310 
13,280 
1.06 


—0.06 
1.00 


—90 


Section 


diameter \ 


symmetrical 
about ¢ mae 
Horizontal 4 


“B bars. Elliptical hoop reinf. 
close to inside face at vert. 
diameter and to outside face 
at horiz. diameter 


Vertical 
KX diameter 
‘A’ bars. Longitudinal 
reinforcement at 
uniform spacing 


above and below 
this line 


Construction 
Joint 


Bar splices alternate 


Bar splices alternate 
above and below 
this line 


e"Clear 


‘C’ bars. Short bars, 
stopped at horiz. 

diameter and tied 
to elliptical hoops 


reverse in 
shown 


Section symmet- 


ie) 
Horizontal PF 


"B" bars. Alternate bars 


rical about ¢ ~y! 


"\’ bars. Longitudinal 
reinforcement at uniform 


position as Spacing each face 


| 
_NerticalZ~ 
* diameter 


"B" bars. Alternate bars 
begin at construction 
joint and end above 
“tH 45° line. Remainder 


ae diameter +4 eu 


¢) 
a Construction 
E& 
re shown 
< 
Y 


iD) {5 


fo Hy Horizontal 
Giemeten: 45° 


joint 


45° 


“B" bars. Alternate bars 
reverse In position as 


KE ip “B" bars. Alternate bare <e '" 
eee ‘i extend from45°lineto SX RT 
lap at opposite constr. 


ct begin near invert and 
end at 45° line 


2" Clear 


ae "F’ bars. Stop at 45° lines 
% 'A’ bars. Longitudinal reinf. 


Section symmet\ y 
I Fical about ¢ 


2"Clear 


a 
ie cas: 
{0 44 Bar splices alternate 
‘oA above and below 
N this line 7 


Bar splices alternatefl>.. ¢ 
above and below [f-- 
this line ——_, fFO of 


WW 


C bars. Alternate bars 
begin at construction 


Construction joint and lap with “F" 


prrcaite 


"D" bars. Alternate bars 
begin at 45° line and stoph.4* 
above constr. joint ong oe 


joint bars above. Remainder 


begin near invert and 
end at beginning of 
lap with “F" bars 
side 


SECTIONS 
Fig. 27. Typical transverse sections of Type I conduit. 


44 


After all moments and thrusts are com- 
puted, the resultants are found. Concrete 
stresses are checked for the assumed depth, 
and steel requirements are found by use of 
Fig. 15, as in previous examples. 


In the example, transverse steel require- 
ments are nearly alike at all critical sections; 
hence elliptical hoop reinforcement is most 
economical. By this arrangement reinforce- 
ment is provided adjacent to the tension 
faces of concrete at both vertical and hori- 
zontal diameters, where it is most effective. 
At points of inflection on 45-deg. lines through 
the conduit axis, the reinforcement is at the 
center of the concrete section. Section A, 
Fig. 27, gives the complete arrangement of 
reinforcement. 


“B” bars are 34-in. round bars at 5-in. 
centers, A,= 1.06 sq.in. 


Splices in hoop reinforcement should be 
made above the construction joints, and 
adjacent splices should be staggered. The 
splice lap must be at least 30 bar diameters 
long for 3,000-lb. concrete. 30 & 34 = 22.5-in. 
minimum. 


Additional transverse reinforcement is de- 
sirable below the horizontal diameter, since 
the elliptical reinforcement is not close to 
the tension face in the thickened section. 
Small bars, tied to alternate “B” bars, are 
satisfactory, so arbitrarily make ‘“‘C” bars 
5g-in. round bars at 10-in. centers. 


Volume of concrete 


I 


3.27(r + t)?— 3.14r? 
3.27(7 + 1)i Bae 
= 55.4 cu.ft. per lin-ft. 


Longitudinal reinforcement 
= (0.002 times gross area 


Total = 0.002 & 144 X 55.4 = 16.0 sq.in. 


“A” Bars: 5£-in. round at 13-in. centers 
= 0.29 sq.in. per foot 


16 


0.29 = 56 spaces at 13-in. centers required 


Construction Joints 


If construction joints are necessary near 
the base of the side walls, they should be 
cast with some locking action as shown in 
Fig. 27, and should be perpendicular to ad- 
jacent concrete faces. The joint of Section B, 
Fig. 27, is difficult to form when elliptical 
reinforcement is used, as the bars occur 
where the groove should be located. For a 
general discussion on construction joints, 
see page 25. 


Form construction for a culvert on Pacheco Pass realign- 
ment, Santa Clara County, Calif. The old highway bridge 
is to be razed. 


Elliptical Versus Circular Reinforcement 


Elliptical hoop reinforcement is advantageous when 
tension steel requirements are nearly alike at vertical 
and horizontal diameters and no compression reinforce- 
ment is required. The elliptical hoops concentrate the 
steel at these critical sections where it is most efficient, 
without the necessity for two concentric layers. At 
diagonal 45-deg. lines the hoops pass through the gravity 
axis of the concrete section where ordinarily the bending 
moment is negligible. Elliptical reinforcement is difficult 
to bend and place, however, and when there is uncer- 
tainty regarding the way this may be done, the arrange- 
ment of reinforcement shown in Fig. 27, Section A 
—Alternate, should be adopted. 


Two layers of concentric reinforcement are economical 
when the concrete is thick enough to make compression 
reinforcement effective. Some saving in concrete can 
then be made by carrying part of the moment and 
thrust on the compression reinforcement. This happens 
under the assumed working stresses at values of ¢ greater 
than about 13 in. 

The size of conduit is also to be considered in selecting 
one or two-layer reinforcement. For large conduits there 
is opportunity for development of unusual loads of some 
significance as, for instance, unsymmetrical earth pres- 
sures. A reversal of moment at a section can then be 
resisted by the original compression steel acting as 
tension steel, without distress. 


Conduits of about 15-ft. diameter, or larger, should 
ordinarily have transverse reinforcement over the outer 
face at the crown to resist moments induced by lateral 
pressures during compaction of backfill at the sides. 


Fig. 28 illustrates two slight modifications in the cross 
section of Type I conduits. In Fig. 28 (a) the bottom 
face of invert is bounded by straight lines rather than 
the arc of a circle. The outer face of the section in 
Fig. 28 (b) consists entirely of segments of straight 
lines. Either of these modifications may be advan- 
tageous in obtaining simpler excavation or less expen- 
sive outside forms. The design coefficients apply with 
sufficient accuracy to either case. 


0.618 (r+t) 


0.382 (r+t) 


0.828 (r+t) 


. 0.586 (r+t) 


0.586 (r+t) 


0.414 (r+t) 


a 


0.618 (r+t) 


oO oon 


o 


0.362 (r+t) 


a 


——-— 


t) IL 0.164 (r+t) 


(r+ 
(b) 


Fig. 28. Alternate sections for Type I conduit. 


Rs 
F Sy Pes eee 
0.764 (r+t) aa72 


45 


TABLE XIV. Typical Designs of Type I Culverts or Conduits 


Waterway 1h Section Dimensions 
opening i ile? 
sq.ft. age! (see r t x y fc bars 
'. Fig. 27)) ft. |in. | ft.-in. | ftin. | size-spacing 
1.5-5|Sec.A} 3} 6] 1-4 Des oe - 6 
28.3 5.5-10 | Sec. A} 3 | 6] 1-4 Des He lye - 51% 
; 10.5-15 | Sec. A] 3 | 7] 1-4% | 2- 244] 49 - 6 
15.5-20 | Sec. A 3] 8| 1-5 2- 3 yo — 516 
15-5] Sec. A} 4} 7| 1-9 2-10 yo —- 5% 
50.3 5.5-10 | Sec. A] 4 | 8] 1-914] 2-10% | 149 - 54 
; 10.5-15 |} Sec. Af 4) 9} 1-10 7} 2-1] 54¢ -— 6 
15.5-20 | Sec. A} 4 | 10} 1-10 | 3- 0 54¢ — § 
150) | SeCaay eon le Orlp2-2 3- 6 54e - 51% 
785 5.5-10 | Sec. A} 5 | 9] 2-244 | 3- 644| 34% - 7 
‘ 10!5—15 | See. AUS | 12-3 3- 8 4? - 6% 
15.5-20 | Sec. A |] 5 | 12] 2-314 | 3- 844 | 34% —- 6 
1.5- 5 | Sec. A | 6 | 9 2-7 4. 2 34¢ -— 6 
; 10.5-15 | Sec. A | 6 | 12] 2-8 4- 4 ike - 7 
15.5-20 | Sec. B |} 6 | 13] 2-844 | 4- 44% | Ke - 6 
1.5- 5 | Sec. A] 7 | 11] 3-014 | 4-10% | 34% - 5% 
153.9 5.5-10 | Sec. A | 7 | 12] 3-014 |4-11144 |] 34% - 5 
, 10.5-15 | Sec. B | 7 | 14] 3-144 | 5- 044 | Ke - 6 
15.5—20 | Sec. B | 7 | 16 | 3-2 Sh Ze — 6 


Transverse reinforcement Lead Volume of 
: concrete 
a”? bars eq)? bars eeyn? bars te bars sree 
size-spacing | size-spacing | size-spacing | size-spacing bd 
LUA eee oet AME | bee es oe A Notas As & ge -— 15 11.8 
T4O =S 1S NO ete ae eee ee oe -— 15 11.8 
a eee Aa ics igen eA! oer sea lY4e — 12 USEF 
Ye a) tl eter a Es, te: oe oe - 12 esi 
a UR rade oto Malas, bane l44¢—- 12 18.4 
165 se Lee ae ee. lo¢ - 12 20.9 
LA Petal AIPA Ol abr tery Ne MBM Sy, Yo — 14 235 
10 = 10g eres te yee eee Yo —- ]2 26.1 
AS Dra Rae a eae ey A ey, l4e -— 12 26.5 
TK ee arte Oa Paes Aiea) Bs oc oo hh Yo — 14 29.6 
GN eke al ean Cote om eee aN Mee ae ya — ]2 36.0 
UE ad PA en acca ee Ny Se Ameer yo - jl 39.2 
Sob a) De Sie pean ae ok ae ee Yo —- 14 35.9 
BO ae Nt Lal caterers tcrcmeae! || te ere Ya - 12 39.6 
Bern en ems ne ot OP a. an 54% -— 13 47.1 
ie -— 7 Ze — 6 54% — 14] 34% - 12 51.0 
SAO AT Vin Ne A crencepseal | Makerere yo — 12 51.0 
SOG) =o 104. ee ae ees Cee | eee ree 546 -— 13 5503 
Iae —- 644) Ke - 6%] % - 13 | %% —- 12 64.1 
ir — 6 ine — 6 54 — 12 | 34% - 14 Aeatih 


Typical Designs 


Typical designs of buried conduits, Type I, are given 
in Table XIV for cover ranging from 1% to 20 ft. Two 
arrangements of reinforcement, Sections A and B, are 
specified. These are shown in Fig. 27. Basic design con- 
ditions are given in ““Typical Designs’, page 29, and 
elsewhere in the text. 


Type II Culverts or Conduits 


The cross section shown in Fig. 29 is recommended 
for special purposes as described in “Choice of Culvert 
Shape”, page 20. This typical sewer or storm drain 
section has about the same hydraulic radius as an 
equivalent circular section. The area of opening is equal 
to 4.00r?, where r is the inside radius of the circular 
segment below the horizontal diameter. The radius of 
an equivalent circular section is therefore equal to 


4.00r? 
pe 1416 2 1.128r. The clear span or clear depth of an 


equivalent square box culvert is equal to 2.00r, exactly 
the same as the length of the horizontal diameter of 
the Type IT conduit. 


A comparison of Fig. 29 with Fig. 25 will show that 
the sections are identical below the horizontal dia- 
meters. The upper part of Type II is drawn as follows: 


At points marked ® on the horizontal diameter at 
the inside face, arcs of radius 2r are turned up through 
angles of 48 deg. 10 min. Lines representing these 
angles intersect at © on the vertical diameter, at a 
distance of 1.118r above the horizontal diameter. Using 
® as a center and a radius of 0.5r, an arc is inscribed 


46 


as shown, completing the closure. This last arc connects 
and is tangent to the arcs of radius 2r. 

The thickness of section varies uniformly from ¢ at 
the horizontal diameter to 0.5¢ at the lines making 
angles of 48 deg. 10 min. with the horizontal at ©. 


Variable 


1616r+0.5t 


Reinforcement \ 


not shown ae DD 
am 
48°10 X©) 
@ Horizontal. diameter Gahan 
PROPERTIES OF SECTION 26°34’ ;o 


Area of opening=4.00r? / i 
Area of concrete “4.G1(ret 512r? 
HYDRAULIC VALUES: = // \ 


Hydraulic radius =0,553r 
Section flowing full ) 


Max. hydraulic adic 0049 


(Depth of flow =2.00r) 
‘ 
eas. about ¢4 


\ 


yeuics) diameter 
\ 


.618 (r+t) 


(Water area=3.40r2) 


Fig. 29. Cross section of Type II culvert or conduit. 


The remaining section at the crown has a uniform 
thickness of 0.5¢. Outside faces of these sections are 
arcs of circles drawn as shown in Fig. 29. 

Effects of the various load conditions used for design 
of box and circular culverts have also been determined 
for Type II conduits. Table XV gives moment, thrust 
and shear coefficients in terms of the load factors and 
for various values of r and ¢. 

Points on the transverse section of the conduit are 
closely spaced, in order that changes in sign and magni- 
tude of coefficients may be accurately followed. These 
points may be located on any Type II conduit by laying 
off the angles tabulated just to the right of the half- 
section above Table XV. The angles are centered at 
the intersection of the horizontal and vertical diameters, 
but it should be noted that tabulated thrusts and shears 
are not perpendicular and parallel, respectively, to the 


lines of such angles. Thrusts are on lines tangent to the 
neutral axis which connects all the points. Shears are 
perpendicular to the neutral axis at the various points. 

The design coefficients of Table XV are not as precise 
as those of Table XII, since fundamental constants for 
Type II conduits cannot be expressed exactly as certain 


i 
powers of (- + :) ort (- + a) The factors listed at 


the top of columns in Table XV are approximations 
of the complicated theoretical expressions they replace. 
Errors resulting from their use are negligible, however, 
for conduits of the proportions required for culverts 
or sewers. 

As in the case of Type I conduits, preliminary designs 
of Type II conduits may be made—and some final 
designs as well—by use of coefficients at the critical 
points: crown, invert and horizontal diameter. Point 6 


TABLE XV. Coefficients for Moment, M, Thrust, N, and Shear, V, in Type II Conduits 


Location of points 


Angle at 
center with 
horizontal 


Point Point 


SIGNS 


Angle at + Moment, M, indicates tension on inside face. 
center with mane : ' 
herizontal + Thrust, NV, indicates compression on section. 


+90° 


Crown 


+ Shear, V, indicates that the summation of 
forces at the left of the section acts outward 
when viewed from within. 


UNITS 


Moments in ft.lb.; thrusts and shears in lb. 
(For P, w and T in lb.; A, r and t in ft.) 


*This load condition results from water inside conduit to top, with no other hydrostatic head. 


of high internal hydrostatic head. 


IV V VI 

aaa Uniform rokeas be py Pressure from Uniform Triangular Hydrostatic 

ection vertical load Seer aL contained water lateral load lateral load head pressure 
MeN eee NS row (one iv’) i lin (eave ey ie ley 
P( ee P P |t( ray) t( ot t( =) r2(r+=)| 2 72 (ree)? wires) w(r+) T(r+2)3 T(r+2)2 T(r+2)2 hr(r+2) hr | hr 

r+) GUS EERE, 2 2 2 2 2 2 2 

Crown | +.046/ +.06 | .00 | +16.6]—-— 14 0 | +13 |- 56 0 | -—.219 | +1.1 0.0 | -.214 | +0.85 | 0.00 |+ 7.8 | —79 0 
1 +.041 | +.09 | +.06 }+15.1]/—- 8]+ 17] +11 |— 52] +18 | -—.193 | +1.0 | -0.4 | —.193 | +0.79 | -0.29 | + 6.8 | —74 | +17 
2 +.008 | +.20 | +.11 }+ 4.8} + 19 | + 39 | + 1 39] +35 | +.007 | +0.6 | -0.6 | —.024 | +0.60 | -0.57 |— 1.5 | -64 | +25 
5 —.032 | +.30 | +.13 |- 9.5} + 50 |] + 53 | -11 |—-— 32] +34 | +.202 | +0.4 | -0.5 | +.176 | +0.41 | -0.59 | -— 8.5 | —Ol | +16 
4 ~.075 | +.40 | +.11 |-26.9| + 89 | + 57 | -21 |— 27| +27 | +.342 | +0.2 | -0.3 | +.357 | +0.22 | -0.50 | -11.6 | -58 | + 6 
5 ~—.110 | +.46 | +.06 |—45.7] +133 | + 52 | -27 |- 23] +13 | +.411 0.0 | -0.1 | +.494 | +0.07 | -0.27 | -11.4] -59 | -— 5 
6 —.120 | +.50 | -.02 |-59.9 | +183 | + 35 | -28 |-— 22] - 8 | +.385 0.0 | +0.2 | +.535 | +0.01 | +0.10 | — 8.3 | -60 | -14 
Hor. Dia. —.115 | +.50 | —.06 |-64.0 | +208 | + 14 | -26 |- 25] -20 | +.335 0.0 | +0.4 | +.507 | 0.00 | +0.31 | — 5.7 | -62 | -18 
7 —.107 | +.49 | —.08 | -66.2 | +228 0 | -22 |- 26] -32 | +.265 0.0 | +0.6 | +.442 | +0.03 | +0.55 | — 2.2 | -63 | -23 
8 080 46 | =-14 1=65.1 14267 |— 31 1 — 8 |\— 34} =59) | +2083 | +011 | +08) |)+.236 '+0.18 || +1.03' | + 6.2 | —67 | —=33 
9 —.006 | +.19 | —.35 | -30.9 | +176 | -208 | + 7 |-— 90] -41 | —.146 | +0.8 | +0.6 | —.076 | +1.19 | +1.12 | +11.2 | -7 0 
10 +.078 | +.09 | —.26 | +25.5 | +126 | -178 | +20 |-110] -49 | -.337 | +1.0 | +0.6 | —.356 | +1.19 | +1.01 | +11.7 | -—79 ae 
el +.133| .00|—.17 | +65.3|+ 66 |-123 | +33 |-132} -43 | -.490 | +1.2 | +0.5 | —.599 | +1.99 | +0.84 | +13.2 | -80 if. 
12 +.161 | —.05 | —.06 | +88.2| + 20 |- 47 | +41 |-153] -16 | —.586 | +1.3 | +0.2 | —.758 | +2.29 | +0.30 | +14.7 | -82 sic 
Invert | +.166/-.06 | .00 | +91.2|+ 14 0 | +42 |-158 0 | -.600 | +1.4 0.0 | —.781 | +2.35 | 0.00 | +14.8 | -84 0 


The conduit is not recommended for cases 


47 


Completed culvert under heavy fill, Pacheco Pass realign- 


Example: Design of Transverse Section of 
Type II Conduit 
Assumed data: 
Required waterway opening = 255 sq.ft. 
Depth of embankment over conduit = 20 ft. 
Average earth pressure conditions, namely: 


Weight of earth fill = 100 lb. per cu.ft. 


Total vertical load, P, on conduit equals weight 
of earth prism above conduit (Case II, page 17). 


Truck loads dissipated before reaching top ofconduit. 
No hydrostatic head above crown. 
Recommended design stresses given on page 26. 


For an opening of 255 sq.ft., the radius of conduit is: 


ment, Santa Clara County, Calif. = = =O ft) approx. 
may have slightly higher moments than at the hori- Estimate that ¢ equals 19 in. and check stresses at the 


zontal diameter, but resultant moment and thrust are horizontal diameter due to vertical load, P, only. 


usually greater at the latter point. 

Table XVI is a condensed tabulation 
of moments and thrusts at critical sections 
in Type IT conduits. Load conditions are 
divided into two groups according to the 
signs of moments they produce. The 
second group includes coefficients for uni- 
form and triangular lateral loads, which 
reduce moments produced by the first 
group. Shear values are not given in Table 
XVI as they do not control under the 
assumed load conditions. 

Design by use of Table XVI is facili- 
tated by the fact that points of inflection 
are nearly fixed for all combinations of the 
assumed load conditions. There is a pair 
of points of zero moment located on the 
top portion of the culvert, each making 
an angle of about 65 deg. with the hori- 
zontal at the intersection of the principal 
axes. The remaining pair, also symmetrical 
about the vertical axis, is located slightly 
below Point 9, and is about 40 deg. down 
from the horizontal diameter. 

In some designs the thickness, 0.5é, at 
the crown will be controlled by the con- 
crete stresses at that point. Twice this 
thickness, or /, at the horizontal diameter 
and invert will then be sufficient for their 
respective stress conditions. In other 
designs, the controlling section is at the 
invert, the same thickness being sufficient 
at the horizontal diameter and half that 
thickness, 0.5¢, also being sufficient at the 
crown. Studies made on typical designs 
have indicated, however, that the propor- 
tions of Type II are well chosen to meet 
the assumed load conditions. 


48 


TABLE XVI. Coefficients for Moment, M, and Thrust, N, at 
Critical Sections of Type II Conduits 


Sections 

Load conditions 
M coeff. (algebraic part) 
N coeff. (algebraic part) 


Horizontal Center 
diameter of invert 


N M N 


I. Uniform vertical load 
P (m5) 
IP 
II. Conduit weight 
ANZ 
t (+ ay 
ry ( =) 
ru 
III. Press. from cont. water 


r2 (+5) 


r2 


VI. Hydro. head pressure 
(+5) 
IV. Uniform lateral load 
2 
w (+5) 
(+5) 
w (reo 
V. Triangular lateral load 
3 
T (+5) 
2 
ve (cea) 


hr 
hr 


Load factors: 


t 
Outside width of conduit = 2(r + f) BREETAR UN BPG EE Ih P(r + 5) 


19 = — 0.115 X 38,340 X 8.79 
= 2(8 + 191) baw 19.17 ft. = — 38,760 ft.lb. (tension on 
A : outside face) 
Uniform vertical load, P a * ee SOFT N = +0.50P = +.0.50 X 38,340 


Uniform lateral load: = + 19,170 lb. (compr.) 


20 x 100 Equivalent moment is: 
w, lb. per sq.ft. = put Saall 667 Nad" 
3 M,=M+ Ep 
Triangular lateral load: 19 
; 100 TOO = 2:0 
T, lb. per ft. of height = ——- = 33 i 2 
3 = 38,760 + 2 
Dimensions: r = 8 Pee b= 5316 = 49,940 ft.lb. 


In Fig. 15, for d = 19 — 2.5 = 16.5 in. and 
M,= 49.9 ft.kips: 
A’,=0 A =2.30 sq.in. 


(- fia 5) = 8.79 ft. 


Computation Schedule for Type II Conduit. r=8 Ft. A; = 2.30 = = 1.24 sq.in. 
Sections The trial thickness, f = 19 in., is ade- 


quate for the principal load and is assumed 
for computing reinforcement areas at 
crown, horizontal diameter and invert by 
use of Table XVI. 

Tabulation of moments and thrusts in 
the computation schedule follows routine 
procedures discussed in previous examples. 
Note that in this case one must consider 
the thickness of 0.5¢ in computing steel 
areas at the crown, and ¢ for other critical 
sections. 


Load conditions Horizontal Center 


Moment, M Crown diameter of invert 


M N M N 
ft.lb; lb. ft.lb. lb. 


Thrust, NV 
rust M N 
ft.lb. lb. 


I. Uniform vertical load 
3 +15,500 
N: +2,300 170 —2,300 


II. Conduit weight 
M: +2,030 
NV: +2,890 


III. Press. from cont. water 
: +7,310 -14,630 


: Transverse reinforcement: See Fig. 31. 
N: —3,580 —1,600 


Crown: 

1. Inside face—use 5£-in. round 
bars at 5-in. centers, As= 0.74 sq.in. 
per foot. These bars are symmetrical 
about the vertical diameter, and ad- 
jacent bars alternate in length. Half 
stop at the upper points of inflection, 
and the remainder 7 in. beyond. See 
page 48 for discussion. 


IV. Uniform lateral load 
M: 11,290 +17,260 
IN: +6,450 
V. Triangular lateral load 
M: —4,800 +11,360 
N: +2,170 


Total M: +8,750 32,580 
Total N: +7,150 


(1) Crown: 


d'=7? 9,522.95 in. 


Na" 
DE 


2. Outside face—use 14-in. round 
bars at 12-in. centers, A’, = 0.20 sq.in. 
per foot. These bars are a precaution 
against reversal of moment at crown 


due to unforeseen loads. 


Horizontal diameter: 

Outside face—use 34-in. round bars 
1,150 at 6-in. centers, As= 0.88 sq.in. per 
foot. Alternate bars have different 
lengths. Half reach from the base to 
the upper point of inflection, where 
they are tied to the 14-in. round bars. 
The other half start at the construc- 
tion joint and end at the beginning 
of the lap. 


(2) Horiz. dia. and invert: 


10,090 44,430 


A (Fig. 15): 1.12 ; 2.03 


_ WN _(b.), ¥ -0.11 
18,000° 0.40 ; 


Ag (sq.in.): 0.72 5 1:92 


49 


Invert: 

Inside face—use 1-in. round bars at 
5-in. centers, A4,= 1.90 sq.in. per foot. 
These bars are not symmetrical about 
the vertical diameter, and alternate 
bars reverse in position—half starting 
where the 45-deg. line from center cuts 
the base and stopping, say, 12 in. past 
the construction joint on the opposite 
side. 


Volume of concrete 
= 4.67(r + t)?— 5.12r? 
= 4.67(8 + 1.58)?— 5.12 x 8? 
= 101 cu.ft. per lin.ft. 


Longitudinal reinforcement 
= (.002 times gross area 


Total = 0.002 X 144 X 101 = 29.1 sq.in. 


29.1 
If 5-in. round bars are to be used, ~~ 031 


= 94 bars will be required. These bars 
should be spaced uniformly in one or two 
layers, as shown in Fig. 31, except that 
three groups of five l-in. round bars each 
are used in the base. The 1-in. round bars 
are used for additional temperature rein- 
forcement in the thick sections and to resist bending 
in the conduit caused by any possible longitudinal 
beam action. 

It is worth while to compare the Type II section 
just designed with the section required for a Type I 
conduit under the same conditions. 

The radius for a circular opening of 255 sq.ft. is 


255 


r=Vaqq = 9.01 ft., say, 9 ft. 


For comparison, the same depth of fill, 20 ft., is 
assumed, although if the invert grade line is fixed, an 
equivalent Type I section is not as high as thé Type II 
section, and would therefore have a greater depth of 
fill—in this case slightly more than 22 ft. 

Based on a radius of 9 ft., and 20 ft. of fill, the Type I 
and Type II sections compare as follows: 


Type I Type II 
Concrete thickness, ¢ (in.): 20 19 down to 9.5 
Volume of concrete: (cu.ft. per lin.ft.) 118 101 
Longitudinal reinforcement (sq.in.): 34.0 29.1 
Transverse reinforcement 
Crown 
As (sq.in. per foot): 1.83 0.72 
A’, (sq.in. per foot): 0.20 0.20 
Horizontal diameter 
As (sq.in. per foot): 1.56 0.90 
A’, (sq.in. per foot) : 0.25 0 
Invert 
As (sq.in. per foot): 1.66 1.92 


It is evident from the comparison that consideration 
should be given to the Type II shape for large conduits 
whenever conditions permit its adoption. 

Typical designs based on average field conditions are 
not presented for Type II conduits. 


50 


"¢12"o.c. Lap bars just past 
the points of inflection. 


3.$5"o.c. Extend half of bars 
30 bar dia. past points of 
inflection 


Ne %" > 6"o.c. Alternate bars 
\ . NO ate at const. joint and 
extend to upper point of 
inflection. Remainder 
start below const. joint 
and stop at beginning 
of lap 


19" 


a — 2" Clear 

bo od Longitudinal bars are 
H 54" 12"0.c. except 
three groups af base 


git 5-1" Longit. bars 
equally spaced 
I"d 5"o.c. Bars 

alternate as shown 


@ 5-1"? Bars 


Fig. 31. Transverse section of Type II conduit designed for 20-ft. fill. 


Head Walls, Wing Walls and Cutoffs 


Good practice in head wall design and location de- 
pends largely upon the judgment of the engineer. The 
basic considerations involving permanence or safety of 
structure, efficiency, and cost are the same here as for 
the culvert proper, but they cannot be as arbitrarily 
applied. Each location presents some new problem if 
only in the execution of details, and the engineer must 
adjust his general design to meet special requirements. 


Some type of head wall is desirable for even small, 
unimportant culverts. The upstream end of the culvert 
must be protected from water getting behind the con- 
crete, saturating the backfill and carrying away light 
material. This “‘piping” action is quickly aggravated 
during storm flows, damaging and sometimes under- 
mining the structures within a short time. Any saving 
made by eliminating head walls may be offset many 
times by high maintenance charges. It should be noted 
that head walls are even more necessary for light, flexible 
pipe culverts than for those of reinforced concrete. The 
former borrow strength, stability and weight from the 
backfill, which therefore must be carefully protected. 


Since the concrete plant used for the culvert barrel 
is available for the head walls, the cost of the latter is 
reduced materially from what it would be if concrete 
were used in head walls alone. This should be remem- 
bered in cost studies involving other construction ma- 
terials. Of particular significance also is the fact that 
a much larger part of the total cost of a concrete struc- 
ture is for unskilled labor and local materials than is 
the case for other types. 


A downstream head wall is used chiefly to protect 


foundations from scour in silted stream beds. A com- 
mon occurrence is for erosion to start a short distance 
downstream from a culvert and to advance upstream, 
becoming more serious as it proceeds. If a head wall 
or cutoff excends down to firm foundation the culvert 
will not be endangered. The eroded channel can then 
be filled and riprapped at a convenient time. Dry 
channels subject to sudden and heavy storm flows are 
especially exposed to this type of erosion. 

Head walls are located parallel to the roadway, 
usually near the point where top of culvert meets the 
sloping embankment surface. A saving in head wall 
height can be made by lengthening the culvert, and 
one should compare the added culvert cost with this 
saving. The possibility of future widening of roadway 
should also be considered before head walls are located. 
Ample width should be provided when there is un- 
certainty in this respect. 

Cutoff or toe walls at inlet and outlet of culverts 
are helpful not only in preventing scour, but also in 
anchoring the structure in place and in reaching firmer 
foundation. The minimum depth below bottom slab is 
usually specified as 2 ft., with the provision that it 
may be increased at the discretion of the supervising 
engineer. Observations made on the character of the 
channel will indicate whether a cutting or a filling 
action is in progress. Rocky, boulder-strewn beds, dif- 
ferent from surrounding surface, mean that erosion is 
occurring, so cutoff walls should be deeply founded. 

Wing walls are used as extensions of head walls for 
large structures, to provide grealer protection for 
embankment material and to prevent the fill from 
encroaching on the waterway. They also have important 
hydraulic qualities which may be utilized in obtaining 
maximum capacity of culvert. In the usual case of 
irregularly shaped channels, the wing walls direct the 
flow into the culvert. Their efficiency in doing this 
affects the capacity more than one might think. It is 
true, of course, that any size of culvert with any kind 
of entrance will carry a large amount of water provided 
there is sufficient head. Creating the necessary head 
may involve flooding a large area of farm land or even 
overtopping the roadway, including softening of the 
embankment and other damage. An efficient culvert 
must carry the expected flow without backing up the 
water more than 1 ft., say, above top of culvert. 

A comprehensive series of experiments* made by the 
University of Iowa in cooperation with the United 
States Bureau of Public Roads have shown that different 
entrance conditions of culverts may cause variations in 
rates of flow up to 50 per cent. 

These experiments show that the two principal factors 
which control the maximum discharge are entrance 
losses and friction losses. Entrance loss is affected by 
the shape of the structure at and near the entrance; 
friction loss by the smoothness and uniformity of the 
culvert walls. That friction losses are important is 
revealed by comparison of flow through corrugated 
pipe and reinforced concrete pipe or box culverts. The 


View of culvert division walls showing details of rounded 
entrance. The capacity is thus increased by reducing 
inlet losses. 


following is one of a large number of similar experiments. 

A 24-in. corrugated pipe culvert, 30 ft. long, carried 
about 23 per cent less water per sq.ft. of waterway 
than a 24x24-in. box culvert of equal length. This 
box culvert had a square cornered entrance. Beveling 
its entrance—simply done in concrete construction— 
increased its capacity 7 to 9 per cent and made the 
difference in capacilies even more striking. An experi- 
ment on a similar box culvert having a rounded entrance 
of very short radius revealed that this latter type is 
the most efficient, as the capacity was increased 8 to 
12 per cent over the capacity obtained by a square 
cornered entrance. It is worth while, therefore, to design 
culverts with rounded entrances even at the slightly 
higher forming cost. 

No general rule can be given for best radius of 
curvature for rounded entrances. Any short radius will 
improve entrance conditions, a large radius not being 
more efficient, proportionately, than a short radius. For 
small culverts a radius of one-half the clear span will 
reduce entrance losses nearly 50 per cent from losses 
due to a square cornered entrance. 


*The Flow of Water Through Culverts, Bulletin 1, University of 
Iowa, Iowa City, Iowa. For a summary of results see ‘Flow 
Through Culverts’, Public Works, Vol. 57, No. 8, September, 
1926. 


51 


The angle with the channel axis to which wing walls 
should be set depends on several factors. Their main 
purpose is to form a transition between channel and 
culvert. The less abrupt and disturbing this transition 
is, the smaller will be the entrance losses. When there 
is a change in direction of stream flow at the culvert 
entrance, the wing walls are best made unsymmetrical 
in length and position. The one at the inside of the 
curve is usually made short and nearly perpendicular 
to the culvert, while the wing wall at the outside is 
long and placed at a strategic angle to deflect the main 
flow into the culvert without turbulence. 


For the usual location in which culvert and channel 
axes are the same, symmetrical wing walls at 45-deg. 
inclinations are most often adopted. They should be 
located so that inside faces are flush with the edge 
of the culvert opening. Slightly greater efficiency is 
claimed for wing walls having angles of 20 deg. with 
the axis, but in view of the possibility of water cutting 
in back of the wing walls such small angles should not 
be arbitrarily used. 


Very attractive structures can be achieved by using 
curved wing walls such as those illustrated above. 
Entrance losses are thus reduced to a minimum and 
some advantage is gained in stability against lateral 
pressures. I’orming costs are higher, however, because 
of the curved surfaces. 


Details 


Fig. 32 illustrates some details of straight end walls 
cast integrally with the culvert. The height of wall 
depends on the elevation of sloping embankment surface 
and the length is such that the embankment is pro- 


52 


Semicircular culvert 
with curving wing 
walls. One of many 
constructed by the 
Tennessee Valley 
Authority. 


tected from direct impact of water. Cutoff walls extend 
down below the limit of erosion, often taken as 3-ft. 
minimum. 

Some features of Fig. 32 refer also to wing walls 
inclined to the head wall, as long as the connection is 
integral. Short L-bars placed horizontally at the con- 
nection, as shown, prevent cracking due to horizontal 
bending. The wall section at this point must be heavy 
enough for this and also for shear due to the lateral loads. 

The wall section out from the culvert must be designed 
as a retaining wall*, independently of the restraint at 
culvert. An additional layer of light reinforcement near 
the exposed face is used in thick walls to resist shrinkage 
and temperature effects. 


Large wing walls are usually cast with a definite joint 
at the culvert head wall, with the expectation that 
lateral pressures will therefore cause no damage to the 
culvert. The joint detail is important, as wing wall 
troubles nearly always spring from poor joints. 

Joints are of two general types depending on the 
anticipated magnitude of lateral pressure. Where low 
pressures are expected, a type of joint which will close 
slightly under wing wall movement is often adopted. 
Two details of this type are shown in Fig. 33, (a) and 
(b). Type (a) is poor for structural as well as hydraulic 
reasons. The narrow joint can accommodate very little 
tilting at top of wing wall without bearing on the culvert 
side wall. Cracks or spalled concrete may occur at the 
joint to mar the appearance. For hydraulic efficiency, 
the exposed face of wing wall should fit flush with the 


*See Concrete Information sheet Small Retaining Walls, free 
in the United States and Canada, upon request to Portland 
Cement Association. 


PROGRESSIVE STEPS IN CULVERT CONSTRUCTION 


From top to bottom the views show: 
a—Placing of reinforcement and forms at inlet. 
b—Placing concrete in floor slab. 
c—Finishing the apron with a wood float. 
d—Curing of floor slab and erection of inner wall forms. 


In this case the floor and apron were cast integrally with 
the walls up to a construction joint 1 ft. above the floor. 


side of culvert opening, as previously discussed. Detail 
(b) is elaborate but improved over type (a). 


if lateral pressures against wing wall are indeterminate 
and possibly high, the joint should be detailed so that 
wall movement cannot damage the culvert. Fig. 33 (c) 
is of this type, but is otherwise unsatisfactory since 
wall movement will open the joint and allow backfill 
material to be carried away. Type (d) has proved very 
satisfactory, as heavy pressures can tilt the wing wall 
without opening the joint. 


Temperature reinforcement 


af Upstream 
channel bank 


as bars turned 
j ical wall 
into vertical w NZ 


Section designed asa = 
cantilever beam in Bary 
Parts of wall not 
adjacent to culvert 
designed for stability, 
and toresist earth 
pressures at all 
critical points 


SECTION THRU 
END WALL 


Fig. 32. Details of straight end walls cast integrally with 
culvert. 


53 


Invert section of the Southwestern Outfall Sewer, Louis- 
ville, Ky. Note the painted concrete and lead water stop 
at the vertical joint. Short dowel bars are employed to tie 
adjacent sections together. 


It is common practice to cast high wing walls to tilt 
backwards l in. per foot of height above footing. 
Lateral pressures are presumed to tilt the wall forward 
to the desired position. 


Water stops fa. oO: 
not shown f5-%¢ 


Culvert 
Culvert reinf. 
not shown 


rt 
i 
=f. 
v 

UF 
abe 


Fig. 33. Details of wing wall joint at culvert. 


Although worthy of attention, the joint detail is not 
as important if the inlet floor is a continuous reinforced 


Printed in U.S.A. 


slab, upon which wing walls are integrally cast. Forward 
sliding or tilting of wall due to poor foundations is thus 
largely eliminated. The vertical wall joints must run 
into a horizontal floor joint, preferably the bell type, 
separating culvert floor and apron. 


Joint filler may consist of bituminous felt or pre- 
molded rubber, and copper or rubber water strips may 
be added for watertightness. 


Head walls and wing walls are made as thin as 8 in. 
for small structures, with 10 or 12-in. thickness com- 
mon for average cases. 


Joint details are excellently portrayed in this construction 
view of the Southwestern Outfall Sewer, Louisville, Ky. 
Horizontal construction joints in the foreground are keyed 
and have vertical bars protruding from the previously 
cast invert section, thus insuring a strong, watertight 
connection in the side walls. A continuous lead strip or 
water stop is partly embedded in the concrete at the 
vertical joint ready for casting the next section. Over-all 
dimensions of the sewer at its largest section are 23 ft. 
2-in. width and 32 ft. 7-in. height. 


T-30 


7 pectinases: 


Portland Cement Association 


& 


Bier x 


| Pre Rigg 
i Si eeigey 


: 


REISSUE SAS NOSES 


ee 
seni ieee 


g | 
5 £ 


fk 


Liberal use of color is featured in the exterior walls of Le Bonheur Children’s Hospital, 
Memphis, Tenn. Colored aggregates, ranging from deep buff to light pink and embedded 
in concrete to which yellow pigment was added, give a warm buff surface at the entrance 


to the Education and Research wing. All aggregate-transfer surfaces ware ground smooth. 


J. Frazer Smith & Associates, Memphis, Tenn.—architect-engineer. Harmon Con- 7 


ed ‘Pirrncnisensereanions 


Lora AIMS P ONE AN THE 


struction Co., Memphis, Tenn., and Oklahoma City, Okla.—contractor. 


At West Point, Neb., the architectural con- 
crete Cuming County Court House has 
approximately 1,700 sq.ft. of aggregate- 
transfer wall areas. These surfaces are 
covered with a mixture of 65 per cent dark 
cedar grey and 35 per cent alpine red 
marble chips and contrast with the grout- 


cleaned exposed concrete walls. 
Backlund & Jackson, Omaha, Neb. — 


architect-engineer. Parsons Construction 
Co., Omaha, Neb.—contractor. 


Portland Cement Association 
33 West Grand Avenue 
Chicago 10, Illinois 


Copyright 1956 by Portland Cement Association 


Liner Layout 1 
Preliminary Preparation of Liners 2 
Application of Adhesive 3 
Spreading of Aggregates 3 
Multicolor Designs 5 
Drying of Liners 5 
Surface Textures 5 
Placing Liners in Forms By eee beset ts 6 
Corners, Construction Joints and Other Details 8 
Placing ‘Concrete. 3 4 =, cal Ws = sae Gn 8 
Removing Forms . =... ¢ 9s < = 9s = 99) 9S 
Finishing. se ews 2 nO 
Patching we we us le 
Aggregates. 8 oe 6 ee ee el 
Equipment 2 26. 3 «© 3 9s Os a fo lo Sue eee 


The activities of the Portland Cement Association, a national organization, are limited to scientific resear 
the development of new or improved products and methods, technical service, promotion and educatior 
effort (including safety work), and are primarily designed to improve and extend the uses of portla 
cement and concrete. The manifold program of the Association and its varied services to cement users ¢ 
made possible by the financial support of over 70 member companies in the United States and Canac 
engaged in the manufacture and sale of a very large proportion of all portland cement used in these tf’ 
countries. A current list of member companies will be furnished on request. 


TEXTURE 


Aggregate transfer is a method of obtaining color and tex- 
ture in cast-in-place architectural concrete by embed- 
ding special, selected colored aggregates in the exposed 
surface. It is practicable for either small decorative areas 
or all exposed surfaces of a structure. Since by this method 
the more expensive special aggregates are confined to a 
thin surface layer of the concrete, an attractive color treat- 
ment is obtained economically. 

Briefly, the aggregate-transfer method of surface treat- 
ment is as follows: The special aggregates are held in an 
adhesive on form liners; the liners are installed in the 
forms; concrete is placed and cured; and, finally, forms 
and liners are removed. The aggregates become embedded 
in and bonded to the concrete to such an extent that they 
are transferred from the liners to the concrete, creating a 
durable colored surface. An aggregate-transfer surface is 
attractive whether it is left untreated or given a special 
surface finish, and in either case requires practically no 
maintenance. 

In addition, special textures may be achieved by using 
different methods of preparing the liners or by giving the 
exposed surface various treatments after the liners are re- 
moved. This manual presents recommended construction 
procedures for the aggregate-transfer method. 


LINER LAYOUT 


Form liners, specially prepared with selected aggregates, 
are required. Before the liners are coated with aggregate, 
they should be laid out according to the same principles 
that apply to form liners in general when they are used in 
the building of architectural concrete walls.* Although 
the joints between liner panels will be inconspicuous, the 
layout should be symmetrical so that the joints are in keep- 


*See Forms for Architectural Concrete, available free only 
in the United States and Canada on request to the Portland 
Cement Association. 


IN ARCHITECTURAL CONCRETE 
BY AGGREGATE TRANSFER 


ing with the main architectural features of the building or 
of the surface under consideration. Vertical joints between 
panels should be staggered with the vertical joints in the 
form sheathing, as shown in Fig. 1. Horizontal construc- 
tion joints in a concrete wall are planned in advance to 
coincide with the horizontal edges of liner panels. 


The outer wall forms are erected first and carefully 
aligned and braced. Plywood is preferred for form sheath- 
ing but accurately fitted dressed lumber may be used. The 
sheathing must provide a solid backing for the liners; open 
sheathing may result in bulging of the liners and give an 
uneven wall surface. 


Plywood 1 in. thick is a satisfactory liner material, 
although sheet metal, cardboard or heavy waterproofed 
paper may be used for special conditions such as the form- 
ing of curved surfaces. Plywood liners are rigid enough to 
permit a panel to be handled and erected without disturb- 
ing the aggregate placed on its surface. With reasonable 
care plywood liners may be used several times, which will 
help to reduce unit costs. A liner panel should not be larger 
than 4x8 ft., the maximum size that can be conveniently 
handled by two men when the panel has been covered 
with aggregate. 


Since a liner panel cannot be cut readily once the aggre- 
gate is placed, it should be accurately cut and properly 
fitted in the forms beforehand. The amount of cutting and 
fitting will depend on the number of intersecting walls 
and the conditions at the corners. Fig. 2 illustrates a corner 
condition that would require much cutting and fitting. On 
large, unbroken wall surfaces, if intermediate panels are 
cut to proper sizes, only the end panels must be prefitted. 
Individual panels or a discontinuous series need not be 
prefitted. Between panels, joints, which should be no 
wider than 32 in., should be filled with gun-grade calking 
compound. To obtain true, straight edges and tight joints, 
it is highly desirable to cut the liners with a bench saw. 


PRELIMINARY PREPARATION 
OF LINERS 


After the liners have been cut and fitted, the working sur- 
face should be oiled lightly with a No. 10 motor oil or any 
good grade of form oil. Some of the water-resistant adhe- 
sive* that is used to attach aggregates to liners should be 
thinned to the consistency of lacquer (about 50 per cent 
adhesive and 50 per cent thinner), brushed on the liners 
and allowed to dry for 24 hours. This treatment will pro- 
tect the surface. 

Strips of wood or plywood 14 in. thick and %4 in. wide 
are fastened to the edges of each panel with staples or 
Yg-in. brads spaced every 6 in. (see Fig. 3). These edge 
strips hold the aggregates to a sharp line, assure good 
aggregate coverage at joints and protect the aggregates 
along the edges when panels are handled. Before they are 
Aggregate-transfer fastened to the edges of the panels the strips should be 
formBners coated with paraffin to prevent aggregate particles from 

adhering to them. For curved edges or other special con- 

ie Aggregate-transfer form liners are shown in ditions strips of waxed heavy cardboard may be used. 
place. Note staggered joints. Rustication strips or other incised forming, such as 
shown in Fig. 4, are also attached to liners at this time. If 
heavy strips or molds are used they should be lightly 
tacked in position and then firmly nailed or screwed from 
the back of the liner. Before liners are removed from the 


Q Staggered vertical joints 


*Special adhesive (362B cement) made by Allied Finish- 
ing Specialties Co., 2639 West Grand Ave., Chicago, IIl., 
or equal. 


Liner panels are cut and prefitted at a corner 
before the aggregate is placed. 


Waxed strips to protect aggregate along the 


edges are attached to a liner panel. 


a V-groove strips attached to a liner panel separate 
the colors in a patterned design. 


hardened concrete, these nails or screws should be taken 
out so that the heavy pattern framework will be left in 
the concrete until the wood has dried thoroughly; then the 
strips or molds can be pulled away easily without breaking 
the edges of the concrete. 


APPLICATION OF ADHESIVE 


The prepared liners are now fastened to a vibrating table 
and spread with the special adhesive (see Fig. 5). The 
adhesive should be water-resistant so that it will not be 
softened by wet concrete or by rain. It should be strong 
enough that aggregate particles will not be dislodged when 
liners are handled or concrete is placed, but it should not 
be so strong that it will damage liners when they are 
stripped from the concrete, thus preventing their re-use. 
The most successful adhesive consists of nitro-cellulose, 
dammar gum and acetate. The thickness of adhesive will 
vary depending on the size of the aggregate to be used 
and the type of finish desired. 

Aggregates must be applied immediately after the ad- 
hesive has been spread because of its tendency to “skin 
over” in 20 minutes or less. During extremely hot weather, 
especially with low humidity, the adhesive may skin over 
very quickly, making it impossible to apply aggregates 
properly. To overcome this difficulty the work should be 
done under a shelter or early in the day when temperatures 
are lower. Another means of delaying skinning is to add a 
small amount of retarder to the adhesive. 


A special adhesive is spread to a uniform depth 


on a liner panel with toothed trowels. 


SPREADING OF AGGREGATES 


Aggregates must be uniform in size—14 to % in., 48 to 
14 in., or Y% to ¥ in—surface-dry and well shaped for 
adequate embedment in the concrete. Crushed aggregates 
should be as nearly cubical as possible; thin, flat pieces or 
slivers will not transfer satisfactorily. Fig. 6 illustrates the 
difference between good and poor particle shapes. 
Although a variety of materials may be used for special 
facing aggregates, marble, granite and ceramics are most 
generally used.* It is often possible to obtain marble aggre- 
gates locally from a dealer in terrazzo supplies.** When 
these special materials are not readily available, local ag- 
gregate may be satisfactory, depending on its hardness, 


~ *For a more complete discussion of special facing aggre- 
gates see page 11. 

**A partial list of manufacturers of special facing ag- 
gregates is available from the Portland Cement Association, 
33 West Grand Ave., Chicago 10, IIl. 


Aggregate 


Flat particles may not transfer 


Adhesive Liner These particles may be dislodged 


GooD PARTICLE SHAPES POOR PARTICLE SHAPES 


S| Properly shaped aggregate particles are essen- 
tial for good transfer from panel to concrete. 


shape and color. After being washed and screened, many 
gravels have suitable colors for aggregate transfer. 

When two or more colored aggregates are to be com- 
bined, small quantities may be mixed by being placed on 
a piece of canvas and rolled back and forth several times 
by two men; large quantities may be placed on a platform 
or floor and mixed by shoveling. 

The method of placing aggregate on a liner depends on 
the size of the area to be covered. Small panels can be 
covered by sprinkling the aggregate by hand as shown in 
Fig. 7. For larger areas, such as 4x8-ft. panels, a small V- 


Ns 


Step |. Draw design layout on liner or transfer from stencil 


ee Pins a 


Step 2. Position 2%>- in. fiberboard divider strips (waxed) with 
common pins 


CLQLL SL, 


Aggregate is spread by hand when only small 


areas are to be covered. 


Step 3. Outline design with divider strips 


ade REM oS ey Ae 


Step 4. Apply adhesive and aggregate to areas A and 
allow adhesive to harden overnight 


Step 5. Remove divider strips and apply adhesive and 
aggregate of different color to areas B. Vibrate 
and allow to harden. 


Ey Drawings show the procedure for making panels 


Aggregate is spread with a V-shaped hopper 


where large areas are involved. with multicolor designs. 


shaped hopper may be used to spread aggregate evenly as 
shown in Fig. 8. (Details for building such a hopper are 
given in Fig. 22.) After the aggregate is spread, the liner 
is vibrated, and any additional aggregate that is needed to 
obtain complete coverage is added by hand. To assure uni- 
form surface coverage, a vibrating table should be used. 
Its impulses must be directed horizontally and so adjusted 
as to pack and settle the aggregate without causing the 
particles to roll or jump. If aggregate particles become 
coated with adhesive on the top or sides they will not bond 
with the concrete. (Details of a vibrating table are shown 
in Fig. 23.) 


MULTICOLOR DESIGNS 


Liners may be prepared with designs in two or more 
colors in a manner similar to that already described except 
that each color of aggregate is placed on the liners on a 
different day. Temporary divider strips should be used to 
separate the colors and outline the design. The adhesive is 
spread on those areas where one color is to appear, the 
aggregate is distributed and the liner panels allowed to 
set overnight. The next day excess aggregate is shaken 
off, divider strips are removed, and adhesive and aggre- 
gate are spread on areas that are to be of a different color. 
The process should be repeated for each color used. Fig. 
9 illustrates a typical design carried out with two dif- 
ferently colored aggregates. 


10) Liner panels are stacked to permit air circulation 
for proper drying. 


DRYING OF LINERS 


After the aggregate has been placed, the adhesive should 
be allowed to dry for at least 24 hours before the liner is 
used; a longer drying period may be necessary if the atmos- 
phere is cool or damp. During the time that the liners are 
drying they may be stacked, one above the other, on 2x4’s 
separated by 2-in. blocks. Keeping the liners apart, as 
shown in Fig. 10, protects them from damage and per- 
mits air to circulate for adequate drying. Properly stacked 
liners may be stored indefinitely. 

Liners that are allowed to dry for a week or two before 
they are needed will usually be easier to strip from the 
concrete. After the adhesive has hardened, liner panels 
should be tilted on edge so that excess aggregate will fall 
off. They should be inspected for uniform and complete 
aggregate coverage and, where necessary, additional aggre- 
gate should be applied according to the method suggested 
for patching liners (see page 10). 


SURFACE TEXTURES 


Several different surface textures that require very little 
or no surface finishing may be produced by varying the 
manner in which adhesives and aggregates are placed on 
the liners. (See photographs of aggregate-transfer panels 
on back cover for typical results.) 


1. Trowel reveal (light). Adhesive is applied to a liner 
with a toothed trowel having seven points per inch (see 
drawing on the left in Fig. 11). This results in a layer of 
adhesive suitable for aggregate 14 to 3% in. in size. Before 
the adhesive is applied it should be thinned with approx- 
imately 15 per cent by volume of lacquer thinner. The 
aggregate reveal obtained by this liner treatment is very 
uniform and requires no surface finishing. 

2. Trowel reveal (heavy). This method is similar to 
the previous one. Aggregate 38 to 14 in. or 14 to % in. is 
used and the adhesive is applied with a trowel having five 
points per inch (drawing on the right in Fig. 11). Less 
thinner is required in the adhesive as the aggregate be- 
comes larger; no thinner is necessary with 7g-in. aggregate. 


ae 


7 teeth per inch 


3 | 


64 


5 teeth per inch 


Trowels for producing (left) light reveal or (right) 
heavy reveal. 


3. Rough reveal. A rough texture can be produced by 
using a built-up adhesive such as a mixture of 50 per cent 
plaster-grade perlite and 50 per cent adhesive by volume. 
Because the perlite will absorb some of the adhesive, a 
thinner must be added to keep the material from becom- 
ing too viscous. This mixture should be spread to a unt- 
form thickness by screeding it with a sx 46-in. steel bar 
equipped with projecting adjustable pegs near each end to 
control the required thickness of adhesive. To aid in level- 
ing the mixture to a uniform depth the liner should be 
vibrated. For %4- to *6-in. aggregate the adhesive layer 
should be *32 to ' in.; for 38- to 4-in. aggregate it should 
be %2 to 46 in. When liners are removed the surface of 
the concrete is wire-brushed to remove excess adhesive 
(see page 10). 


4, Veined finish. Adhesive and aggregate are applied 
as in method 1. Then a mixture of 10 parts of perlite to 
1 part of molding plaster and enough water for a stiff 
consistency is troweled or dashed on the aggregate-coated 
liner to produce a veined effect or, if desired, a definite 
pattern. When liners are removed the weak plaster-and- 
perlite mixture is easily wire-brushed from the surface to 
produce the desired effect. 


5. Sand finish. Adhesive should be thinned to the con- 
sistency of flat wall paint and carefully brushed out on 
the liners in the same manner in which an interior wall is 
painted. This must be done during cool weather or in a 
cooled room because the thin coating of adhesive dries 
rapidly in higher temperatures. Sand passing a No. 20 
screen and retained on a No. 30 screen is used as the liner 
aggregate. The sand particles, being very small, give such 
dense coverage that no further surface treatment is neces- 
sary when the liners are removed. 


PLACING LINERS IN FORMS 


Aggregate-coated liners weigh from 2 to 21 psf. A panel 
as large as 4x8 ft. should be handled by two men. Even 
though properly placed aggregate is not easily dislodged, 
rough handling should be avoided. 

The edge strips (see page 2), which protect the aggre- 
gate on the panels where it is most vulnerable, should not 
be removed until necessary. The strips at the bottom and 
along the side adjoining the previously placed panel are 
removed just before the liner panel is positioned in the 
form. The edge strip along the other side is removed just 
before the next panel is set, as shown in Fig. 12. If the 
strip at the top coincides with a construction joint, it 
should remain on the liner until the concrete in the lift 
has been placed; it is removed at the same time that the 
liner is taken off. Strips are easily removed without tools 
and may be re-used. 


Before liners are set and attached, the forms should be 
examined and any protruding nails or other irregularities 
removed so that the liners will fit tightly against the form 
sheathing. At abutting edges, liners must fit snugly and 
be exactly flush to avoid objectionable joint marks. To pre- 
vent leakage at the joints a narrow strip of suitable calk- 
ing compound is applied to the edge of the previously 
placed panel, as shown in Fig. 13. An excess amount of 
calking compound should be avoided. If the next panel is 
shoved firmly against the one in place (see Fig. 14), a well- 
filled joint not more than ‘2 in. wide will result. 

When the liners are properly positioned they are fas- 
tened to the forms with 8-in. wire brads spaced about 
6 in. on centers near the edges and on 16-in. centers inter- 
mediately. Loosening of aggregate particles can be avoided 
if the brads are driven carefully. 

After the outer curtain of reinforcing bars is erected, 
liners should be checked for loosened panels and for areas 
where aggregate has been knocked off. Additional brads 
may be required to refasten panels and keep the joints 


12 To prevent damage, protective edge strips are 


not removed until necessary. 


14 | A liner panel is shoved firmly against a pre- 
viously placed panel to form a tight joint. 


should have a soft rubber pad that rests against the aggre- 
gate-transfer liner to protect the surface from damage. 
When tierods are removed they should be pulled out from 
the side of the form opposite the liner. 


2x2 stop 


panels; an excess amount should be avoided. 


A he < 
FE} Calking compound is used to seal joints between 


flush. Those areas where aggregate has been knocked off 
are easily repaired by pressing aggregate into a fast-set- 
ting adhesive piece by piece. Generally, unless the liners 
have been greatly mishandled, little repair work needs to 
be done. 

A 2x2 is nailed to the sheathing at the construction 
joint at the top edge of the liner (see Fig. 15) before the 
curtains of wall reinforcement are set. The 2 x 2 acts as a 
concrete stop to form a straight line at the construction 
joint and also holds the outer vertical reinforcing bars 
the proper distance away from the face of the liners to as- 
sure adequate concrete cover over the bars. 

After the reinforcement is placed the inner form is 
erected. Tierod holes should be drilled from the inside face 
toward the outside in one operation with a long drill. An 
improvised drill may be made from a long steel rod that 
is flattened and beveled to a sharp edge at one end. Wales 
on both sides of the forms should be directly opposite 
each other. 

Tierods should be fully removable and of the combina- 
tion spreader-and-tie type that leaves no mark on the wall 
surface other than the hole itself. Only when absolutely Wallecectionashowstrormetandicurtaine ofirein 
necessary should inside spreaders be used, and then each forcement in place. 


Curtains of 
reinforcement 


y 


LS) SSS RSS 


Aggregate-transfer 
liner 


Fully removable ties 


Tierod holes drilled 
from inside face 


SII III IIIS IIE III III PIII IR EI OOS 


Outer forms ‘ liner with aggregate 


SSS 


COCO 


i 
Detail of |: 
Upper Liner i 
ae 
R Form tie or 
Detail of embedded bolt 


Lower Liner 


Vertical Section 
PROCEDURE FOR JOINTS WITH RUSTICATIONS 


Liner joint calked 


Liner is left in place 
until next lift has 


been cast Vertical Section 


PROCEDURE FOR FLUSH JOINTS 
16 Method of making construction joints with aggre- 


gate-transfer liner panels. 


ELL 


Pee 


When either liner A or B is less 
than |6 in.wide the two liners are 
bradded together and aggregate 
is applied first to the narrower 

liner,then to the other. They are 
erected together. 


45° bevel on liner edges 
q seers 


couereeee CCL 
OUD 


maar liners are ae: and 
erected separately, 


RE-ENTRANT CORNER 


Method of obtaining complete aggregate cover- 
age at corners, both outside and re-entrant. 


CORNERS, CONSTRUCTION JOINTS 
AND OTHER DETAILS 


Figs. 16 through 18 show the recommended procedures 
for using the aggregate-transfer method at locations of 
some of the more common details of architectural con- 
crete construction, such as horizontal construction joints— 
both the flush type and the type with rustications—and 
square corners—both outside and re-entrant. The sug- 
gested procedures will provide almost perfect continuity 
of the aggregate finish at joints and corners. In general, 
other forming problems that may arise can also be solved 
with the ideas presented in Figs. 16 through 18. 


PLACING CONCRETE 


Before concrete is placed, the forms and the upper sur- 
face of previously placed, hardened concrete should be 
flushed with water, but a strong hose stream should never 
be directed against the liners because some of the aggre- 
gate may be loosened. A moderate water spray or normal 
rains will cause no damage if the recommended type of 
adhesive has been used. 

Concrete should be proportioned, mixed, handled and 
placed in accordance with good architectural concrete prac- 
tice,* and it should be workable enough that it can readily 
be placed in the interstices of the liner aggregate. Sand in 
the mix should be well graded, with 15 to 30 per cent pass- 


*See Architectural Concrete Specifications, available free 
only in the United States and Canada on request to the Port- 
land Cement Association. 


b's 3" waxed strip Particles at this edge should 


A A not project above edge strip 
{SOTOVSCCCC2800; OO IEA SA IOI ail 
Table Table 
First day 
Table 
ae A and B prepared on same day 
8 
Soy Temporary brace at 
‘on eh est if A exceeds 8" 
[) 
Ns eS 
NR SS 
Nf N 
Ny A . 
NR NPN 
NS SPX B 
NS SEN 
ROCCO POCO ESIOVOVO4 


Brads 
Second day 
PROCEDURE WHERE 
A 1S IG IN.OR LESS 


Table 


PROCEDURE WHERE 
BOTH A AND B EXCEED IGIN. 


Procedure in preparing liner panels for outside 


418) square corners. 


va Hopper and chute 


Aggregate-transfer 
liner 


Reinforcement 


Spud vibrator 


Construction joint 


WZ. 
VL 


19 Each layer of concrete should be vibrated for at 
least 10 seconds to its full depth. 


ing a No. 5O sieve. Air-entrained concrete generally has 
the necessary workability for this type of work. 

As in other architectural concrete construction, the mix 
should contain not more than 614 gal. of water per sack 
of cement and not less than 51/4 sacks of cement per cu.yd. 
of concrete. Concrete consistency will vary with the wall 
thickness but in most cases will be satisfactory when meas- 
ured by a slump of 4 to 5 in. Where concentrations of 
reinforcing bars interfere with the placing of the con- 
crete, it may be necessary to reduce the amount of coarse 
aggregate or, in extreme cases, to limit aggregate size to 
not more than 34 in. in order to avoid honeycombed 
stone pockets. 

Concrete should be placed in layers about 12 in. deep, 
and each layer should be thoroughly vibrated with an in- 
ternal vibrator* for at least 10 seconds to its full depth, 

*See Vibration for Quality Concrete, available free only 


in the United States and Canada on request to the Portland 
Cement Association. 


as shown in Fig. 19, at intervals of about 10 in. along the 
wall. Careful vibration in the first lift, at corners and over 
door and window openings is especially important. At no 
time should a vibrator be permitted to touch a liner panel. 
Spading by hand will not satisfactorily fill the voids of the 
facing aggregate with mortar, nor is external vibration as 
effective as internal vibration. 

Concrete should be placed through a chute or tremie to 
prevent spattering on the facing aggregate. Also, spatter 
from the vibrator should be reduced as much as possible 
by turning off the vibrator each time the spud is with- 
drawn from the concrete. The spud must be inserted to 
the full depth of each new layer of concrete because the 
vibrating action is ineffective beyond 6 in. below the spud. 

Concrete in upturned spandrel beams must be placed 
carefully and correctly. If concrete is placed first to floor 
level and is allowed to harden before concrete is placed in 
the upturned section of the spandrel, an objectionable cold 
joint will appear in the face of the spandrel at the floor 


FX) Aggregate-transfer liners should be removed 
carefully to avoid marring the surface. 


level. On the other hand, if it is placed at once to the full 
height of the spandrel, some of the concrete may flow into 
the floor and sag away from the exterior wall surface. The 
correct procedure is to place concrete to the floor level, or 
slightly above, and allow it to stiffen but not harden be- 
fore resuming placement in the upturned portion. 


REMOVING FORMS 


When the concrete has hardened, forms are removed first 
and the aggregate-transfer liners are stripped from the 
walls later. This delay allows the concrete to harden 
enough that the facing aggregates will not be pulled off 
with the liner. Usually the liners can be taken off after 5 
days, but it may be necessary to allow more delay in cool 
weather. If liners are not to be re-used, they may be left in 
place until the structure is nearly completed to aid in the 
curing process and to protect the surface of the wall dur- 
ing construction. Liner panels can be pried off with a 
beveled 2 x 4, starting at one corner as shown in Fig. 20. 
Once a start has been made at a corner, the rest of the 
panel will usually come off easily. In removing the liners, 
the use of sharp tools or other methods that will mar the 
surface should be avoided. 


FINISHING 


Pleasing surface textures can be obtained economically by 
the methods discussed in “Surface Textures,” pages 5 and 
6, with little or no further surface treatment. 

In addition, a variety of textures, from moderately rough 
to polished, can be produced by various methods of sur- 
face finishing. Generally, the concrete should be cured at 
least 14 days before any surface treatment is started. 

Rough textures may be obtained by several means. Bush- 
hammering produces a slightly roughened surface that has 
a pleasing appearance, but it is usually uneconomical 
except for small areas of special ornamental interest. A 
slightly rougher texture can be produced faster and more 
economically by sandblasting; an area of 300 to 400 sq.ft. 
can be treated per hour with one sandblast nozzle. Since, 
besides deeply revealing the aggregate, blasting etches it 
and changes its color, this effect must be taken into account 
when sandblasting is specified. Samples should be made 
and sandblasted before the method is used on a completed 
wall. This also affords a chance to select the proper sand 
for blasting and to determine the most satisfactory dis- 
tance from nozzle to surface. With the usual nozzle veloc- 
ity and sand used for sandblast cleaning satisfactory re- 
sults are obtained when the nozzle is approximately 5 ft. 
from the surface. 

A smooth, almost polished finish can be produced by 
dry-grinding the surface with a No. 8 grit resin-bonded 


10 


stone until the aggregate is well exposed. For greatest 
economy a high operating speed of 4,500 to 5,500 rpm is 
recommended. Wet-grinding produces satisfactory results 
but it is slower and less economical. After dry-grinding, 
any pits and holes in the surface should be filled with grout. 
To do this, the surface should first be flushed with water; 
then a stiff grout, consisting of 1 volume of blended 
white and grey portland cement to about 214 volumes of 
sand passing the No. 8 sieve, should be applied with a 
fiber brush. The grout should be worked into the voids 
with a rolled-felt rubbing pad on a flexible shaft machine 
operating at the lowest speed; excess grout should be re- 
moved. The surface should be kept damp for 3 days or 
until the grout is hard enough for the final grinding opera- 
tion, which consists of wet-grinding with a No. 80 grit 
stone. After the final grinding, the surface is scrubbed with 
a 15 per cent solution of muriatic acid to brighten the 
color of the aggregate and is then rinsed with water. 

A smoothly ground surface has a quality appearance 
that is of greatest value at building entrances and other 
locations that are subject to close inspection. Grinding, 
like bush-hammering, is an expensive operation and is 
generally used only for small areas. 

The surface obtained by the rough reveal method de- 
scribed on page 6 must be wire-brushed to bring out the 
coarse texture after liners are removed. The adhesive can 
be brushed away more readily after it has dried thoroughly 
for a week or more. Recommended for best results is a 
flexible-shaft power tool equipped with a rotating brush 
that has stiff wire bristles about | in. long and that is oper- 
ated at the slowest speed. The concrete should be hard 
enough that aggregate particles are not dislodged by the 
action of the tool. 


PATCHING 


Any imperfections in surfaces that may occur can be 
patched and, if the work is done carefully, will be difficult 
to detect. The patch should be made before the surround- 
ing areas are finished. The defective area is chipped out 
to a depth of ¥4 to 1 in.; the edges are undercut if possible. 
It is then wetted and filled with mortar mixed to a stiff 
consistency with | part of cement and 24 parts of sand. 
The mortar is placed in two layers, each 7 to Y2 in. 
thick, on successive days. The second layer is struck off 
lg in. below the wall surface and while the mortar is still 
soft, grout-coated particles of the matching aggregate are 
troweled in until an aggregate coverage like that on the 
surrounding areas is obtained. The grout-aggregate mix 
is made with 1 part cement, 2 parts sand and about 6 parts 
aggregate with only enough water to hold it together. 
After the special aggregate is in place the patch is com- 
pacted, floated level with the wall and then kept damp for 


at least 5 days. The patch and surrounding surfaces should 
be given the same finishing treatment. 

To match the color of the patch with the surrounding 
areas several trial mortar mixes should be made with dif- 
ferent percentages of white and grey cement. A small pat 
of each trial mix should then be cured for 5 days and com- 
pared with the wall to determine which of the mixes 
most closely matches the existing color. 


AGGREGATES 


The special facing aggregates most commonly used in the 
ageregate-transfer method are: 

1. Marble aggregates. Crushed marble is a very satis- 
factory material because it comes in many colors, breaks 
into desirable shapes, is available in most localities and is 
reasonable in cost. Marble aggregates come in either light 
or dark shades of green, yellow, red, pink, blue or grey, 
as well as in white or black. 

2. Granite aggregates. Crushed granite is also a de- 
sirable material, especially since it is extremely durable, 
but its range of colors is limited and it is not as readily 
available as marble. Granite aggregates may be white, 
black, grey or pink. 

3. Ceramic aggregates. Ceramic particles are manu- 
factured in a wide range of bright colors and two or more 
colors may be combined to give almost any color or tone 
desired. Ceramics cost about four times as much as marble 
or granite aggregates and thus are generally used only for 
small surface areas or spot ornamentation. 


EQUIPMENT 


In addition to the usual tools found on a construction job, 
the aggregate-transfer method requires the following 
equipment: 

1. Aggregate shaker screen. Aggregate is often avail- 
able already screened to size. If not, it must be screened 
to obtain the correct sizes and to remove particles of dust. 
When the quantity to be screened is small, the work may 
be done with a hand-operated shaker screen, shown in 
Fig. 21. For large amounts of aggregate, a power-operated 
screen may be more economical. 

2. Spreader hopper. A small V-shaped hopper for 
spreading aggregate rapidly over the liner panels may 
be easily constructed of plywood, as shown in Fig. 22. 
Properly used, a hopper of sufficient capacity will give 
about 95 per cent aggregate coverage. 

3. Vibrating table. A high-speed motor with 3,450 
rpm is necessary to obtain the correct type of horizontal 
vibration. Fig. 23 shows details of a vibrating table. 

4. Brad pusher. Brads are driven with a magnetic 
brad pusher. If this is equipped with a slender nozzle, 


Runner 
3 plywood 
swivel arm 


2x2 handle 
4 ft. long 


EE] Details of a hand-operated shaker screen for 
screening aggregates. 


—Length determined by 
the width of liner 


= plywood divider 
+ plywood sides 


GENERAL VIEW 


NG 


ALTERNATE METHOD 


END VIEW 


22) V-shaped hopper for spreading aggregate rapidly 


on large liner panels. 


re lip for clamp hook 


a) 
J... 
he) 


° 
+ 
> plywood top 
fastened with |5 flat- 
head screws 6'0.c. ° 
3 : NS t 
Az 


HALF PLAN OF TABLE TOP HALF PLAN OF TABLE CONSTRUCTION 


i Eccentric mounted 
on motor shaft 


Motor bolted to 
table frame 


Motor mounted verticall —) 
(| hp.- 3,450 rpm) “ 


_—— ef rubber skids- 


SIDE ELEVATION 
5-0" 


2 staple 


|x 8 end braces 


END VIEW OF CLAMP ASSEMBLY 


23 Details of a vibrating table. 


brads can be inserted in the spaces between aggregate 
particles. 

5. Calking gun. Calking compound should have the 
consistency of a heavy plastic paint and should be applied 
with a gun that has a small nozzle. 

6. Vibrator. An internal vibrator with a small spud 
that will pass between reinforcing bars should be used. If 
possible, the vibrator should be electrically operated to 


da ! 


Weight of eccentric must 
be determined by test 
; bolt 


Bout welded 
to g steel plate 


DETAIL OF MOTOR ECCENTRIC 


a An 3 “clamp tightening bolt 
ZZ x4 (ie 
16 
= 4 
WN if 
‘ 
2 \ 
\ 
~ 
ris 5) A 
g § washer 
_— t gimp tack 
“ Washer bent to 
hold nut 
ee 5 


DETAILS OF LINER CLAMP PARTS 


provide better control of starting and stopping. 

7. Trowels. Special toothed trowels (see Fig. 11) should 
be used to spread adhesive in a uniform layer. For thicker 
layers of adhesive a metal screed as described under 
“Rough reveal,” 


page 6, should be used. 


8. Table saw. Because aggregate-transfer liner panels 
must fit snugly, a power saw must be used to cut straight 
true edges on the plywood panels. 


> 


The drawings in this publication are typical designs and should not be used as working drawings. They 
are intended to be helpful in the preparation of complete plans which should be adapted to local conditions 
and should contorm with legal requirements. Working drawings should be prepared and approved by a 


qualified engineer or architect. 


12 


Sill-high walls on the Griswold School, Covina, Calif., have a rough-textured 
surface of exposed colored aggregate. School walls are often marked up by 


children but the rough surface of these walls, not susceptible to chalk or other 
marks, retains its attractive “‘built-in’’ appearance. 


H. L. Gogerty, Los Angeles, Calif.—architect. D. Stewart Kerr, Los 
Angeles, Calif.—associate architect. William C. Crowell Co., Pasadena, 
Calif.—contractor. 


For the remodeled and enlarged offices of the Red-D-Mix Concrete Co., 
Omaha, Neb., colored aggregate was used in the surfaces of this decora- 


tive end wall and of areas above and below the windows and at the main 
entrance. Marble chip aggregates, predominantly a medium green with 
some silver grey and alpine red, provide a distinctive color treatment that 
contrasts with the untreated architectural concrete walls. 


Leo A. Daly Co., Omaha, Neb.—architect-engineer. Parsons Construc- 
tion Co., Omaha, Neb.—contractor. 


Printed in U.S.A. 


1. Ground surface with ceramic aggregates. 2. Sandblasted rough texture. 


hale ss 


3. Sand finish. 


ew 9 i il ro apy ea 
ie Per +d " 4 


iin’ See ee. pea 
bs ¥ ‘4 * 
as 3 sa os 


* 


7. Rough reveal. 


8. Veined finish with color additive. 


Marble aggregates were used in all panels except panels 1 and 3. 


Panels 1, 2, 4, 5 and 7 had been continuously exposed to Chicago weather for nearly 18 
years at the time the photographs were taken. 


Ce 


Contents 


Introduction. ...° ss. 12) tence aan eee 
Section 1. Highway Interchanges . . . . . - - 4 
Section 2. Types of Grade-Separation Structures 6 
Deck Girder 6 
Box Girder 5. oe Sf oetaet ea 
Slab «<0 0° @ 30 OO ee eS 
Rigid Frame 8 
Arch : 9 
Prestressed Girder 9 
Section 3. Design Considerations . . . . . . «./I/ 
Safety. 08 2 9. rr | 
Span Length . . eee se eel 
Vertical Clearance aa Deer Width a ke” Al 
Architectural: Design?2  )=) ase a ee ee 


Section 4. Planning a Grade-Separation Structure . . 12 


Highway over Highway, Unrestricted Site . . . .12 
Determination of Bridge lypem. near ee ee 2 
Span: Lengths” 5) Sane 2sme une nn ane: ee nL 
Supersiructure Dimenstons® s.r ee 

Highway over Railroad, Restricted Site. . . . .13 
Determination of Bridge oe [eo ee 
Span Lengths . . . be at 3p eee en 
Proposed Layouisis.) = 25s ae ee ee 

Highway over Highway, Restricted Site. . . . .13 
Determination oj Bridge lype= ))-an- 
Preliminary Layouts 27.0). 7 ee 
Alternate Solution’; “= oe) ae) ee ee 

Appendix Ay: 2 0) a ses See ee 7 
Appendix Bo 00°.) U2) 3) Senin te a 12, 
Appendix’ C..2 22S) a, 2) eA ee ee 2 


The activities of the Portland Cement Association, a national 
organization, are limited to scientific research, the development 
of new or improved products and methods, technical service, pro- 
motion and educational effort (including safey work), and are 
primarily designed to improve and extend the uses of portland 
cement and concrete. The manifold program of the Association and 
its varied services to cement users are made possible by the finan- 
cial support of over 65 member companies in the United States and 
Canada, engaged in the manufacture and sale of a very large 
proportion of all portland cement used in these two countries. A 
current list of member companies will be furnished on request. 


Copyright 1958 by Portland Cement Association 


Introduction 


The expanded highway program now under way is 
at improving the safety and capacity of our major 
way systems. An important part of this program 
National System of Interstate and Defense High 
which is being designed to handle the traffic of 1 
This system will connect nearly every city in the | 
States with a population of more than 50,000. A 
feature of the program is the construction of grade-si 
tion structures, which are designed to provide safe 
and egress at intersecting highways without t 
disruption. 

Highways are built on all types of terrain and mus 
various urban and rural requirements. As a result, , 
separation structures must be designed to fit variou 
ditions. They must not only satisfy requirements of 


*See “Geometric Design Standards for the National ! 
of Interstate and Defense Highways” (abstracted in : 
dix A, pages 17-18), adopted July 12, 1956, by the Com 
on Planning and Design Policies of the American A 
tion of State Highway Officials. 


rticular sites but also fit into the overall engineering and 
chitectural plan of the highway system. A bridge de- 
med for one site will seldom be usable at another loca- 
m without some modification. In this respect, using 
ncrete is particularly advantageous. Because of its plas- 
ity and adaptability, changes in structural type or archi- 
‘tural form can easily be made. Variety in appearance 
n be obtained and, as shown in the photographs included 
this booklet, pleasing architectural effects can be 
hieved for all parts, from massive abutments to fine 
corative details. 

Concrete is not only adaptable; it is also ruggedly dura- 
e, capable of withstanding the destructive action of 
ather with almost no maintenance. Sturdy, rigid con- 
uction results from the stiffness of the concrete members 
d from the structural continuity that is easily and eco- 
mically attained. Bridge decks can be designed in con- 
ete to carry heavy loads without annoying vibration. 
Exhaustive studies of site conditions, costs and materials 
d to the selection of concrete bridges for the Fort Worth 
xpressway, Pennsylvania Turnpike, Merritt Parkway, 
llywood Freeway and the Alaskan Way. These struc- 


tures and others throughout the country are giving excel- 
lent service and are adding to the safety and appearance 
of our entire highway network. 

Progress in bridge construction calls for continual re- 
view of established procedures to obtain the best possible 
solution to both old and new problems. In this booklet, 
current methods of selecting a bridge for a given site and 
important factors to be considered in the layout of any 
grade-separation structure are discussed. 

In Section 1, general types of highway interchanges in 
common use today are briefly illustrated and described. 
These interchanges involve grade-separation structures 
that permit traffic on each road to maintain an almost 
uninterrupted rate of flow regardless of direction of turn. 
Various types of bridges suitable for interchanges are illus- 
trated and described in Section 2, and the conditions for 
which each is best adapted are discussed. Bridge types con- 
sidered are the deck girder, box girder, slab, rigid frame, 
arch and prestressed girder. In Section 3, important design 
considerations are summarized, and in Section 4 the pro- 
cedure for selecting a suitable grade-separation structure 
is illustrated for three typical situations. 


ESrEe Highway Interchanges 


Normal, open-road flow of traffic will not be interrupted 
at the intersection of two highways if the roadways are 
separated by means of grade-separation structures. Con- 
tinuous and full capacity of both highways can be assured 
by adequate interchange roads and properly designed en- 
tryways to allow turning vehicles to join through traffic 
without interference. 

The selection of interchange type depends on a variety 
of conditions, including volume, type and speed of traffic, 
right-of-way restrictions, and topography at the inter- 
change site (see Fig. 1). A discussion of the selection and 
design of interchanges of several kinds is given in A Policy 
on Geometric Design of Rural Highways, published by the 
American Association of State Highway Officials 1954. * 

Most effective of the various patterns are directional 
interchanges of the kind shown in Fig. 2, designed with 
long ramps having large curvatures. On these, vehicles can 
move from one road to the other with little or no reduction 
in speed. 

*Also see A Policy on Grade Separations for Intersecting 


Highways, American Association of State Highway Officials, 
National Press Building, Washington, D.C., 1944. 


Fig. 1. This view, looking northerly along the Golden State 
Freeway just west of San Fernando, Calif., dramatically illus- 
trates the effect of topography on highway interchanges. 


Courtesy of California State Department of Public Works, Division of Highways. 


Fig. 2. This directional interchange at the intersection of U.S. 80 and the Cabrillo Freeway, San Diego, Calif., allows vehicles to 
change direction with little reduction in speed and without obstruction to through traffic. 


aa! us: ed Ss Z be q % ‘ : 3 


Fig. 3. Service roads for local traffic both flank and pass over the Los Angeles Harbor Freeway through busy industrial and 
residential areas. Interchange is by means of one-way ramps. Courtesy of California State Department of Public Works, Division of Highways. 


Expressways passing through congested residential or 
industrial areas, where right-of-way is restricted, are 
frequently depressed. Local traffic is routed on overpass 
bridges and on service roads parallel to the main highway. 
Access to the expressway is usually infrequent and by 
means of interchanges like those shown in Fig. 3. 

Interchanges discussed in AASHO publications repre- 
sent types in general use, but many variations are possible. 
An outstanding example is the four-level Los Angeles inter- 
change shown in the cover photograph and Fig. 10 (page 
7), with its complex arrangement of freeways and con- 
necting ramps. 

Whatever form is chosen, the interchange can help to 
maintain a constant flow of traffic and to eliminate acci- 
dents due to crosstraffic. 


Fig. 4. This aerial view shows the interchange on the Penn- 
Lincoln Parkway at the entrance to the Squirrel Hill Tunnel 
near Pittsburgh, Pa. Courtesy of Pittsburgh Post-Gazette. 


Eames Types of Grade-Separation Structures 


DECK GIRDER 


In St. Clair County, IIL, a three-span continuous deck or 
T-girder bridge (see Fig. 5) was selected for its architec- 
tural beauty, suitability to the terrain and economic 
feasibility. Open end spans with spill-through abutments 
give the motorist a feeling of unrestricted vision and result 
in an efficient, economical design. 

Span lengths were chosen so that maximum positive de- 
sign moments are approximately equal in all spans. An 
interior span of 621 ft., which allows for future widening 
of the underpass highway, is balanced against end spans of 
48 ft. The bridge has four 13-ft. lanes, a 4-ft. wide median 
strip and a 2-ft. wide safety curb on each side of the road- 
way. Slab depth is 7 in. and girders are spaced at about 
7 ft. on centers. 

The superstructure is divided into two parts by a sealed 
joint running the full length of the bridge at the roadway 
centerline; each half of the structure was cast in one con- 
tinuous operation. Open piers between abutments reduce 
objectionable noise under the structure and provide good 
distribution of light. 

Reactions from the superstructure are transmitted to the 
piers through conventional bearings. In some structures 
it is possible to extend continuity by eliminating the inter- 
mediate bearings and making the deck integral with the 
piers. Elimination of continuity between the deck and 
abutments may be desirable if some movement of the abut- 
ments under lateral forces is expected, but integration of 
the deck with some of the interior supports is usually 
advantageous. * 


*Information on this type of design is found in Continuous 
Concrete Bridges, available from the Portland Cement Asso- 
ciation in the United States and Canada. 


Fig. 5. Maximum visibility is provided by this bridge in St. 
Clair County, Ill., which has open piers and open end spans 
with spill-through abutments. Design: Illinois Division of 
Highways. Construction: Maurice Hoeffken Co., Belleville, Ill. 


m me Se Sg ee 


Fig. 6. Use of concrete for all parts, including the handrails, is 
typical of grade-separation structures on the Detroit Industrial 
Expressway. Design: Michigan State Highway Department. 
Construction: L. A. Davidson, Lansing, Mich. 


The continuous T-girder shown in Fig. 6 carries east- 
bound traffic of the Detroit Industrial Expressway over 
Ecorse Road in Detroit, Mich. The soffits of the ends of the 
girders are straight rather than curved like those of the 
bridge shown in Fig. 5. Either design is pleasing. The use 
of concrete for all parts of the Detroit bridge, including 
the handrails, resulted in a harmonious appearance and low 
maintenance costs. 

The bridge has two 65-ft. spans and two 5344-ft. spans 
and carries a roadway 36 ft. wide. Girders cast integrally 
with a 7%4-in. thick deck slab are spaced at 6 ft. on centers 
and vary in depth from 2 ft. 7 in. at midspan to 5 ft. 8 in. 
at interior piers. 

This bridge is typical of grade-separation structures used 
on the Detroit Industrial Expressway as well as on the 
Detroit-Toledo Expressway and the Ann Arbor Belt Line. 


BOX GIRDER 


The concrete box-girder bridge, frequently used at grade 
separations when a low depth-to-span ratio is required, may 
be supported by one- or two-column bents as shown in the 
cutaway view in Fig. 7 and usually consists of one or more 
boxlike cells with transverse diaphragms. The box-girder 
section is efficient for resisting moments and enables a 
designer to use concrete for spans longer than those gen- 
erally considered economical for T-girders. 

Box-girder bridges are particularly suitable for skewed 
sites and curved superelevated roadways requiring extra 
torsional strength. There is generally enough space in both 
top and bottom slabs for reinforcement to be placed in a 
single layer. This simplifies construction and permits max- 
imum effectiveness of all bars. Conduits can be carried in 
the cells. 


Fig. 7. Box-girder superstructures—a typical one is shown here 
in a cutaway view—are well suited for both vertical loads and 
torsional effects. 


The two-span bridge in the foreground of Fig. 8 is a 
box girder functioning as part of a rigid frame. The design, 
typical of the other bridges shown in the photograph, was 
selected on the basis of a comparative cost analysis and 
because it harmonized with the surroundings. This bridge, 
carrying North Broadway over the Hollywood Freeway, is 
one of many similar structures in the Los Angeles area. 

Closed abutments and a shallow superstructure were used 
because of the width of the depressed six-lane divided high- 
way and its limited right-of-way. To secure shallow depth, 
advantage was taken of continuity by making the super- 
structure integral with abutments and center pier. The 
bridge is designed for H20-S16 loading of the AASHO 
Standard Specifications for Highway Bridges (1953) plus 
a special loading for vehicles of the Los Angeles Transit 
Authority. Girders vary in depth from 3 ft. 3 in. at midspan 


erence 


Los Angeles Sip eee: “a 
rato 


I 
| 


I 
| 
| 
| 
| 


Fig. 8. Vertical clearance and right-of-way limitations were 
easily satisfied by the use of rigid-frame box-girder construc- 
tion for these bridges in Los Angeles, Calif. Design: City of 
Los Angeles. Construction: Guy FE. Atkinson Co., San Fran- 
cisco, Calif. 


to 5 ft. at supports. The two equal spans are 62 ft. long 
and carry a roadway 60 ft. wide. 

Another example of rigid-frame box-girder construction 
is the Highland Creek Underpass (see Fig. 9), which is 
located east of Toronto, Ont., Canada, and carries local 
traffic over Highway 2A on a 115-ft. span. Formwork for 
the structure was designed to create a rough-board texture. 

The bridges in Fig. 10 are typical of multilevel grade- 
separation structures used by the California State Depart- 
ment of Public Works, Division of Highways. The top two 
levels are continuous hollow box girders while the third 
level is continuous-slab construction. This four-level inter- 
change in Los Angeles provides nonstop traffic for the 
Hollywood Freeway (top level) and the Harbor Freeway 
(third level), with interchange ramps between the two 
expressways. The adaptability of concrete to structural, 


RBH GRE TRS GSC REE WEINER 3 GSES ALE EMU CTTL 


Fig. 9. This long-span rigid-frame box-girder bridge near 
Toronto, Ont., Canada, provides safety through maximum vist- 
bility and unrestricted passage. Design: Department of High- 
ways, Ont., Canada. Construction: Bailey Construction Co., 
Toronto, Ont., Canada. 


Fig. 10. Long spans and shallow superstructures are provided 
by box-girder construction in the top two levels of this multi- 
level grade separation in Los Angeles. Design: California State 
Department of Public Works, Division of Highways. Construc- 
tion: James I. Barnes Construction Co., Santa Monica, Calif. 


re 


visual and architectural requirements of interwoven struc- 
tures is well illustrated here. 


SLAB 


Concrete slab bridges are popular and economical struc- 
tures for short-span grade separations. Although slab 
bridges are sometimes composed of one or more simple 
spans, structural continuity is desirable where good foun- 
dation conditions exist or can be provided, because concrete 
is ideally suited to integral construction. With continuity, 
the cost of joint construction and maintenance is greatly 
reduced. Also, a smoother riding surface is secured because 
deflections are decreased and there are fewer joints. 

Continuous slabs are usually suitable for bridges with 
end spans up to approximately 35 ft. and interior spans 
proportionately longer (see page 11). The shallow super- 
structure inherent in slab construction helps solve the com- 
mon problem of vertical clearance. A minimum grade 
differential between the two roadways generally results in 
overall economy because the height of embankments is 
reduced. 

The four-span continuous concrete slab bridge in Coshoc- 
ton, Ohio, shown in Fig. 11, is typical of structures used by 
the Ohio Department of Highways for a series of short 
spans. The 1814-in. slab is designed for 5-20-46 live load, 
as specified by the State of Ohio, equivalent to AASHO 
H20-S16 loading. Interior span lengths of 40 ft. are bal- 
anced by end spans of 32 ft. The bridge carries four 13-ft. 
traffic lanes, a 4-ft. raised median and two 6-ft. sidewalks. 


Fig. 11. Economical short-span bridges are obtained with a 
continuous concrete slab, such as this one in Coshocton, Ohio. 
Design: Ohio Department of Highways, Bridge Bureau. Con- 
struction: V. N. Holderman & Sons, Inc., Columbus, Ohio. 


RIGID FRAME 


The concrete rigid-frame bridge, economical for spans 
ranging from about 35 ft. to 100 ft. or more, provides max- 
imum structural continuity. Integral construction of both 
horizontal and vertical members permits a shallow deck 
and reduces material used in the bridge approaches. As is 
evident in the accompanying photographs, the rigid-frame 


bridge integral with closed abutments and intermediate 
piers is more massive in appearance than the T-girder 
bridge, such as those shown in Figs. 5 and 6. This is only 
one type of rigid frame. A bridge integral with two in- 
termediate piers and free at the abutments is also a rigid 
frame. Because of its monumental appearance, a rigid 
frame is particularly suitable for parkways and boulevards. 

Fig. 12 shows the impressive two-span rigid-frame bridge 
that carries McCutcheon Road over U.S. 40 in St. Louis 
County, Mo. This structure was selected for the site because 
of its economy, appearance and general usefulness. Al- 
though the wingwalls create a feeling of massiveness, the 
curved intrados carried from one embankment to the other 
gives the bridge a graceful appearance. 


Fig. 12. Special architectural effects can be developed economi- 
cally with the rigid-frame bridge. This all-concrete structure 
is in St. Louis County, Mo. Design: Sverdrup & Parcel, Inc., 


St. Louis, Mo. Construction: Israel Bros., Clayton, Ohio. 


Horizontal clearance for each span is approximately 62 
ft., with a minimum vertical clearance of 14 ft. The super- 
structure carries a roadway 44 ft. wide with an additional 
7 ft. 9 in. at each side for curb, sidewalk and handrail. The 
five reinforced concrete frames vary in depth from about 
4 ft. at midspan to a little more than 9 ft. at abutments and 
center columns. The deck slab is 104% in. thick. 


a 


Fig. 13. The shallow superstructure of the solid-slab rigid 
frame minimizes earthwork in bridge approaches. Side slopes 
at this structure in Tucson, Ariz., have been given a protective 
surfacing of pneumatically applied mortar. Design: Bridge 
Division, Arizona State Highway Department. Construction: 


San Xavier Rock & Sand Co., Tucson, Ariz. 


A solid slab without girders serves as the deck of the 
bridge in Fig. 13. This structure carries U.S. 89 over U.S. 
80 in Tucson, Ariz., and accommodates a 72-ft. roadway 
and two 6-ft. sidewalks. Preference was given to this design 
because past experience proved it to be economical and 
because of its general suitability to the terrain. Each span 
provides a horizontal clearance of 341 ft. from the breast- 
wall to the face of the 2-ft. thick center pier. The breastwalls 
and pier are supported by spread footings. Earth slopes 
adjacent to the wingwalls were given a surface of, pneu- 
matically applied mortar to prevent erosion. 

Another solid-slab rigid-frame bridge is illustrated in 
Fig. 14. This bridge, which carries Route 638 over the 
Henry G. Shirley Memorial Highway in Fairfax County, 
Va., adds beauty to the parkway. The slab varies in thick- 
ness from 2 ft. 24% in. at midspan to 6 ft. 1% in. at abut- 
ments. It spans 81 ft. to carry a 26-ft. roadway designed for 
AASHO H-20 loading. The curved intrados of the bridge 


is in harmony with the rolling countryside. 


Fig. 14. Concrete lends itself to many attractive variations in 
architectural form, as shown in this rigid-frame bridge on the 
Henry G. Shirley Memorial Highway in Fairfax County, Va. 
Design: Virginia Department of Highways. Construction: Guy 
H. Lewis & Son, McLean, Va. 


Fig. 15. Maximum driving safety is provided by carrying the 
full roadway width, including shoulders, under structures on 
the Dallas Central Expressway. Design: Texas State Highway 
Department. Construction: Austin Bridge Co., Dallas, Texas. 


Typical of grade-separation structures on the Dallas Cen- 
tral Expressway is the two-span rigid-frame bridge shown 
in Fig. 15, which carries the 48-ft. wide roadway of Monti- 
cello St. over U.S. 75 on two 54-ft. 9-in. spans. The slab 
varies in depth from 1 ft. 4 in. at the center of each span 
to 3 ft. 114 in. at abutments and piers. Comparative cost 
analyses showed this design to be equal to any other in 
first-cost economy. Concrete was chosen for its durability, 
architectural versatility and low maintenance cost. 


ARCH 


The arch, one of the oldest and most graceful of archi- 
tectural forms, is suitable when there is sufficient difference 
between the elevations of intersecting roadways. The con- 
crete arch bridge shown in Fig. 16 carries Brinton Road 
approximately 40 ft. above the Penn-Lincoln Parkway at 
Pittsburgh, Pa. The ribs span 164 ft. and are 6 ft. wide, 
with depth varying from 4 ft. 714 in. at the springing to 2 
ft. 6 in. at the crown. Spandrel columns 3 by 1% ft. in 
cross-section support floor beams that in turn carry a deck 
slab 10 in. thick. The deck accommodates two 12-ft. traffic 
lanes and two 5-ft. sidewalks. An arch was chosen for this 
site because of its beauty and its suitability to the con- 
ditions. 


Fig. 16. The graceful lines of this concrete arch bridge add 
beauty to the scenic Penn-Lincoln Parkway at Pittsburgh, Pa. 
Design: George S. Richardson, Pittsburgh, Pa. Construction: 
Sanctis Construction, Inc., Pittsburgh, Pa. 


PRESTRESSED GIRDER 


Prestressed concrete, a modification of reinforced con- 
crete, takes advantage of high-strength concrete and steel 
and results in members that are graceful in appearance and 
often shallow enough to reduce the cost of retaining walls 
and bridge approaches. Prestressed concrete members are 
comparatively light and easily handled. 


Twelve bridges on the Garden State Parkway, a north- 
south toll route near the New Jersey coast, consist of pre- 
cast-prestressed concrete girders supporting cast-in-place 
deck slabs. Contractors bid only on prestressed concrete 
for these structures although alternate construction was 
allowed. 

Spans vary from about 39 ft. to 60 ft. However, interior 
girders for all bridges are of the same I-shaped cross- 
section and have a 33-in. depth, 6-in. web, 12-in. wide top 
flange and 19-in. bottom flange. Fascia beams are also 33 
in. deep but have a rectangular section to provide a smooth, 
exposed vertical surface. Stress variations in the girders 
due to different span lengths are compensated for by varia- 
tions in the girder spacing and the number of steel strands 
per girder. 

Fig. 17, one of the Garden State Parkway bridges, il- 
lustrates the ease with which precast-prestressed girders 
are handled during erection. The completed structure car- 
ries the Parkway over U.S. 322 and U.S. 40 near Atlantic 
City, N.J., on two 58-ft. simple spans. Girders are spaced 
at 3-ft. 4-in. centers across the 90-ft. roadway width. The 
superstructure is prestressed transversely by cables that 
pass through diaphragms at the third-points of each span. 

The Wisner Blvd. Overpass, shown in Fig. 18, is a 1,420- 
ft. grade-separation structure in New Orleans, La. Use of 
precast-prestressed members not only reduced construction 
time but also permitted uninterrupted traffic on the 42-ft. 
span over two railroad tracks. Each of the other 23 spans 
is 60 ft. long. Eight posttensioned, T-shaped girders were 
used for each span. 


bad 


Lo 


at 


Fig. 18. Site-casting the 192 posttensioned 60-ft. girders needed 
for the Wisner Blvd. Overpass, New Orleans, La., reduced han- 
dling to a minimum. Precast diaphragms were used between 
the beams, which were set 6 ft. 8 in. apart. Design: George A. 
Heft & Co. Construction: Keller Construction Corp. Both are 
of New Orleans. 


1A 


AXA \\\ |e 
fs = & 5 


~ 


Fig. 17. Using precast-prestressed concrete girders facilitates construction and minimizes interference with traffic. This photograph 
shows precast-prestressed girders being erected to carry the Garden State Parkway in New Jersey over U.S. 322 and U.S. 40. 
Design: Gannett, Fleming, Corddry & Carpenter, Inc., Harrisburg, Pa. Gonstruction: S. J. Groves & Sons Co., Woodbridge, N.J. 


ESE Design Considerations 


To develop any new bridge project successfully, de- 
signers must know the requirements to be met. Considera- 
tion must be given to bridge types, span lengths, deck 
widths, clearances, alignment, and sight distances. The 
completed structure must not only provide necessary func- 
tional features but should also add to the overall appear- 
ance, usefulness and safety of the highway system. 

Established standards are helpful as a guide in the de- 
termination of minimum requirements. For highways that 
are part of the National System of Interstate and Defense 
Highways, Tables | and 2 (Appendix B, pages 19-20) give 
the minimums recommended by AASHO. For highways 
that are not part of the National System of Interstate and 
Defense Highways, Tables 3 and 4 (Appendix C, pages 21- 
22) give the minimums recommended by AASHO. 


SAFETY 


It is difficult to show a direct relationship between the 
cost of a grade-separation structure and the safety it af- 
fords. However, there are many valuable safety features 
inherent in good layout practices and, therefore, they are 
obtained without the expenditure of additional money. The 
most functional layout can be, and often is, the safest and 
most economical one. 

The safe structure is one that least restricts motorists. 
A good example is the deck bridge with open end spans, 
similar to the one shown in Fig. 4, page 5. In contrast, 
bridges that have massive, solid abutments are likely to 
give the motorist a feeling of constriction, especially if the 
abutment is close to the edge of the pavement. Generally, 
open end spans are also economical. However, in cases 
where the right-of-way is limited, closed abutments with 
wingwalls may provide the only practical solution. 


SPAN LENGTHS 


The determination of minimum span lengths is controlled 
by clearance requirements, grades, and fill slopes. 

In continuous bridges the ratio of interior-span length 
to end-span length has a direct effect on cost. For this 
reason the optimum ratio should be used whenever pos- 
sible. On the basis of (1) AASHO loadings; (2) concrete 
design stress of {,=0.40 f’.; and (3) use of 3,000-psi con- 
crete, the following ratios of interior to end spans are 
recommended: 


For slab bridges with end spans up to 35 ft.: 1.26:1 

For slab bridges with end spans 35 to 50 ft.: 1.31:1 

For girder bridges with end spans 35 ft. and more: 
1.37:1 to 1.40:1 


In general, if end spans exceed 35 ft., it is more economical 
to use girder construction than a solid slab. 

The span ratios given are for continuous decks that are 
not integral with supports. If superstructures and supports 
are integral or if allowable working stresses or loads are 
changed, some deviations are to be expected. However, the 


values given are usually satisfactory for planning and for 
preliminary cost estimates. 


VERTICAL CLEARANCE AND DECK WIDTHS 


For bridges not on the National System of Interstate and 
Defense Highways, AASHO Standard Specifications for 
Highway Bridges (1953) recommends a minimum vertical 
clearance of 14 ft., plus an allowance for future paving. 
The ideal deck width allows space for both the approach 
pavement and shoulders. AASHO recommends that the 
roadway be at least 6 ft.* wider than the pavement and not 
less than 26 ft. for two traffic lanes. For each additional 
lane the roadway should be widened 10 to 12 ft. 

Bridges on the Interstate System must have a clear height 
of not less than 14 ft. over the entire roadway, including 
the usable width of shoulders. The width of bridges with 
a length of 150 ft. or less between abutments or end sup- 
porting piers is to equal the full approach roadway width, 
including the usable width of shoulders. Barrier curbs on 
bridges longer than 150 ft. are to be offset at least 2 ft. 
from the edge of the through-traffic lane. Also, offsets to the 
face of the parapet or handrail should be at least 3% ft. 
at both the right and the left. 

Although it is desirable to carry the full median strip 
across any bridge, this becomes economically impractical 
when the median is very wide. It is satisfactory in this 
situation to decrease the width of the strip gradually as the 
bridge is approached. Two separate structures, one for each 
direction of traffic, are desirable if it is economically 
feasible. 

In practice there is no general rule governing the transi- 
tion point from a single to a double structure. As one 
example, the Illinois Department of Public Works and 
Buildings, Division of Highways, changes to a double 
bridge at a median width of about 20 ft. 


ARCHITECTURAL DESIGN 


At the outset of the planning stage a grade-separation 
structure should be studied from the architectural as well 
as the structural viewpoint. Although there is no easy rule 
to follow that will ensure the proper aesthetic use of a 
building material, experience has shown that close coop- 
eration between engineer and architect leads to the most 
satisfactory result. 

In the case of a bridge, it is important for the designer 
to recognize that his structure will probably outlast many 
aspects of its surroundings and that foresight is necessary 
to assure lasting beauty. To help achieve this goal, concrete 
offers the advantage of versatility. The choice of bridge 
type as well as of its shape and lines is completely unre- 
stricted by the building material, and a design may be de- 
veloped that is in complete harmony with the surroundings. 


*But 4 ft. when safety curbs or contiguous sidewalks are 
used, or if traffic lane widths exceed 12 ft. 


Il 


ESE Planning a Grade-Separation Structure 


Three typical situations have been selected to illustrate 
the principles of layout of a highway grade-separation 
structure: (1) highway over highway, unrestricted site; 
(2) highway over railroad, restricted site; (3) highway 
over highway, restricted site. 


HIGHWAY OVER HIGHWAY, UNRESTRICTED SITE 


A two-lane, east-west secondary highway 24 ft. wide 
intersects a six-lane, north-south Interstate expressway at 
right angles in open, level country. It is desired to separate 
the intersecting roads by carrying the east-west highway 
over the expressway. The median between north- and south- 
bound expressway traffic lanes is 36 ft. Each 36-ft. road- 
way has 10-ft. shoulders, as shown in Fig. 19. Design live 
load is AASHO H20-S16. 


Determination of Bridge Type 


The selection of a structure to separate traffic at this 
intersection is simplified because there are no space re- 
strictions. As a result, in the layout full attention can be 
given to function and appearance. 

Safest driving conditions for expressway traffic would 
be obtained if the entire roadway, including shoulders, 
were spanned by the secondary highway bridge without the 
use of a center pier. However, the gain in safety would not 
be great enough to justify the increased cost of the long 
span, especially since the pier would occupy only about 
one-tenth of the 36-ft. median width. 

If a center pier is assumed, the expressway will be ac- 
commodated either by a structure with closed abutments, 
of the type shown in Fig. 19(a), or by one with open end 
spans, as sketched in Fig. 19(b). In either case the super- 
structure can consist of slab or slab-and-girder construc- 
tion designed either as a rigid frame, a series of continuous 
spans, or a series of simple spans. 

In open country, the confinement of earth fill is unneces- 


sary. In addition, solid abutments at each side and a pier 
in the middle give the motorist a feeling of constriction, 
causing him to focus his attention on the bridge and to 
“aim” for the center of the passageway. As a result, the 
vehicle usually moves toward the center of the road. 

Open end spans with spill-through abutments provide a 
structure that does not distract the driver’s attention and 
is usually economical. Therefore, closed abutments are 
eliminated in favor of the type shown in Fig. 19(b). Struc- 
tural continuity is adopted to take advantage of the integral 
action of all spans. 


Span Lengths 


The choice of either slab or slab-and-girder construction 
is made by comparing relative costs of each type for the 
indicated span lengths. Each interior span will be about 
651% ft. long if 3-ft. piers are assumed. Tentative end spans 
may be determined by ratios given on page 11. 

If slab construction is used, the ratio 1.31:1 indicates 
end spans of about 50 ft. (6544 + 1.31 = 50 ft.). This 
end-span length eliminates the slab from further considera- 
tion since girder construction is usually more economical 
when end spans exceed 35 ft. With girders, the value 1.37 
gives end spans of about 48 ft. 


Superstructure Dimensions 


Deck width may be determined by following AASHO 
recommendations. Width of the roadway will be equal to 
the pavement width of 24 ft. plus 4 ft., or 28 ft., between 
safety curbs. When 3 ft. is allowed on either side for safety 
curbs and handrails, the overall superstructure will be 34 
ft. wide. 

A 7-in. deck slab is common for H20-S16 loading. For 
this thickness, economical girder spacing varies from 7 ft. 
to 10 ft., as discussed in Continuous Concrete Bridges, 
page 60. If five girders are assumed, spacing can be 7 fe. 
3 in., which leaves a distance of 2 ft. 6 in. from centerline 


Fig. 19. A comparison of bridges with (a) closed abutments and (b) open end spans. 


of outside girder to the exterior bridge face. If desired, 
however, spacing can be altered so that exterior girders are 
flush with the edges of the deck. 

Although the stem width of a T-girder depends on 
several variables, approximate width may be taken to be 


b’ = 0.0025 Vb X L (also shown in Continuous Concrete 
Bridges on page 60), where b is the center-to-center spac- 
ing of girders and L is the length of the end span. When 
dimensions already established are used, 


b’ = 0.0025 7.25 X 12 X 48 x 12 = 13.4 in. 
Experience has shown that a minimum stem width of 17 in. 
is necessary to allow sufficient space for placing reinforce- 
ment; therefore, a width of 17 in. is assumed in this case. 

When girder spacing and stem width have been tenta- 
tively determined, girder depth over interior supports is 
found to be 70 in. (Continuous Concrete Bridges, Fig. 47, 
page 63). If the girders are assumed to have a parabolic 
soffit, approximate midspan depth may be determined by 
dividing support depth by 2.3, an average value for the 
ratio of support to centerline depths for girders of this 
shape. This gives a midspan depth of approximately 31 in. 


HIGHWAY OVER RAILROAD, RESTRICTED SITE 


A four-lane divided Interstate highway is to pass at right 
angles over an existing double-track railroad on which 
traffic must be maintained at all times. Tracks are 14 ft. on 
centers. The two 24-ft. roadways of the highway are paral- 
leled by 10-ft. wide shoulders but are separated by only a 
4.-ft. median strip because of confining topography nearby. 
Sufficient right-of-way is available to allow construction 
of approach fills with 2-to-1 side slopes. 


Determination of Bridge Type 


The main consideration is to provide a bridge that will 
perform its functional requirements efficiently and that can 
be constructed with a minimum of inconvenience to the 
railroad. Units that are both precast and prestressed are 
ideally suited to this situation because of the speed with 
which they can be erected. 

Since the railroad right-of-way at this site does not 


require confinement of fill, closed abutments are not con- 
sidered. Instead a multiple-span bridge that has spill- 
through abutments and a precast-prestressed concrete su- 
perstructure appears most desirable. Features that promote 
good driving conditions on the roadway carried over the 
tracks should, of course, be included in the design. 


Span Lengths 


Well-defined clearance requirements for proper opera- 
tion of railroad equipment determine span lengths and 
vertical height. The Manual for Railway Engineering® es- 
tablishes a minimum horizontal clearance of 8 ft. from 
track centerline to the faces of bridge piers and a minimum 
vertical clearance of 22 ft. from top of rail to soffit of the 
overhead bridge. During construction, minor encroach- 
ments on these minimum clearances may be allowed if 
permission is secured from the railroad. 

According to these specifications, minimum clear span 
over the tracks should be 14 + (2 X 8) = 30 ft. If 2 ft. 
is allowed for depth of superstructure and 22 ft. is added 
for required vertical clearance, grade differential between 
road surface and top of rail is 24 ft. If a 2-to-1 slope for 
fill at the abutments is assumed, the bridge length, includ: 
ing abutments, is approximately 120 ft. 


Proposed Layouts 


A suggested layout involving three 40-ft. simply sup- 
ported spans with precast-prestressed members is shown 
in Fig. 20. Although earth slopes are increased slightly 
and the center span is 7 ft. longer than the required mini- 
mum of 30 ft. clear plus 3-ft. pier width, this plan results in 
maximum duplication of parts because all girders are of 
equal length. However, the cost of a bridge that utilizes 
equal-length girders should be compared with the cost of 
one that has a shorter, shallower center span since a shallow 
superstructure will reduce the earthwork in bridge ap- 
proaches. Also, if precast members of reinforced rather 
than prestressed concrete are used, shorter spans are needed 


*Published by the American Railway Engineering Asso- 
ciation, Chicago, III. 


Fig. 20. Precast-prestressed concrete girders over a double-track railroad. 


14 


to minimize the weight of individual units. 

As an alternate layout, the center span may be reduced 
to 33 ft. with the remaining 87 ft. divided to form a five- 
span structure. 


HIGHWAY OVER HIGHWAY, RESTRICTED SITE 


A non-Interstate freeway to be built within city limits is 
to have four 12-ft. traffic lanes separated by a 4-ft. median 
strip. The freeway will be constructed in a cut and the 
finished grade will be dependent on vertical clearances re- 
quired at several other grade-separation structures. The 
bridge considered in this example is to carry an existing 
roadway 48 ft. wide with a 6-ft. sidewalk at each side across 
the freeway. The location limits the freeway right-of-way 
to 110 ft. 


Determination of Bridge Type 


The most economical bridge is not always the best from 
the functional point of view. For example, a bridge with an 
intermediate pier at the center of the 4-ft. median strip 
would probably be the most economical for this site, but 
to maintain clearances recommended by the AASHO it is 
necessary to span the entire roadway without intermediate 
support. A clear span of 64 ft. complies with AASHO rec- 
ommendations by providing a 6-ft. clearance from edge of 
roadway to face of pier or abutment. 

If a three-span continuous bridge is used, end spans will 
be about 51 ft. long as determined by applying the ap- 
proximate balanced-span ratio of 1.30:1. However, right- 
of-way limitations at the site provide a length of only 22 ft. 
for end spans. As a result, the multiple-span bridge is 
eliminated in favor of a single 64-ft. span with closed abut- 
ments. The rigid-frame bridge is appropriate because of its 
shallow deck and relative economy. For spans up to about 
70 ft. the rigid frame with a solid deck is usually econom- 
ical and is recommended in this case. 

Experience shows that right rigid frames (those without 
skew) of the solid-deck type designed for heavy highway 
loadings have a superstructure depth of about 1/35 at 
midspan and L 15 at abutment faces, where L is the clear 
distance between abutments. If the slab soffit is assumed to 
be parabolic, depth of the superstructure directly above 
the outside edge of pavement will be about 3 ft. 5 in. for a 
span of 64 ft. In contrast, the depth required for a simply 
supported T-girder of the same length is about 4 ft. 3 in. 
for girders spaced at 6 ft. or about 5 ft. 9 in. for girders 
spaced at 9 ft. This comparison indicates one of the ad- 
vantages of structural continuity. 


Preliminary Layout 


A quick, simple method of estimating frame dimensions 
is valuable in preparing architectural studies and prelim- 
inary cost estimates. Referring to Fig. 21, the following 
empirical procedure is applicable to right rigid frames 
carrying heavy highway loading: 

1. Lay out the deck ABA according to roadway require- 

ments. 

2. Determine clear span, L. 

3. Lay out BC equal to about L/35. This value may be 

reduced to L/40 when the foundation is practically 


unyielding; it should be increased when footings rest 
on highly compressible soils. 

. Lay out AD and DE equal to about L/15. 

Draw the soffit curve DCD’ (usually a parabola). 

Determine the elevation of / and G from clearance 

requirements and foundation conditions. 

7. Lay out FG equal to about 1% ft. for 30-ft. spans, 
about 2% ft. for 60-ft. spans, and about 3% ft. for 
90-ft. spans. 

. Connect E and F with a straight line. 


DB 


© 


Fig. 21. Outline of a typical single-span, solid-deck, rigid- 
frame bridge. 


yd. 


Concrete- cu. 


Span _ length- ff. 


Fig. 22. Concrete quantities required per 6-ft. deck width for 
prestressed concrete girder spans shown in Fig. 23. 


AASHO H20 loading 
fo = 4,000psi 
f', = 250,000 psi 


Span length - ft. 


Fig. 23. Depth-to-span relationship for simply supported pre- 
stressed concrete girder bridges. 


9. Determine roadway and curb widths according to 
AASHO specifications, adding about 21% ft. for hand- 
rail construction. 

With the exception of wingwalls, which are controlled 
by site conditions, essential frame dimensions are now 
determined and quantities for preliminary estimates may 
be computed. 


Alternate Solution 


A shallow superstructure can also be achieved by use 


6'-o" 24'-0" 


= 
A 3" concrete wearing surface 


es 


Prestressed girders @ 2-O'c toc . 


a5 
ne) 


of prestressed concrete girders simply supported on closed 
abutments. Fig. 23 shows depths required by spans vary- 
ing from 40 ft. to 80 ft. for two girder arrangements, Types 
I and II, with spacings of 2 ft. and 6 ft. respectively. Fig. 
24 illustrates in cross-section the superstructure of the same 
bridge with the deck slab supported on either of the two 
types of girders and also indicates appropriate overall 
depths. Fig. 22 gives concrete quantities involved in each 
design. Quantities are given for the 6-ft. wide sections 
shown in the sketches in Fig. 23. 


24'- (on 6- 0" 


Cay say 


Prestressed girders @ 6-O'c toc 


Fig. 24. Alternate layouts of prestressed concrete girders in a bridge superstructure. 


vhs) 


Appendix A 


and Defense Highways* 


Geometric Design Standards for the National System of Interstate 


AMERICAN ASSOCIATION OF STATE HIGHWAY OFFICIALS 


ADOPTED JULY 12, 1956 


GENERAL 


The National System of Interstate and Defense High- 
ways is the most important in the United States. It carries 
more traffic per mile than any other comparable national 
system and includes the roads of greatest significance to 
the economic welfare and defense of the Nation. The high- 
ways of this system must be designed in keeping with their 
importance as the backbone of the Nation’s highway sys- 
tems. To this end they must be designed with control of 
access to insure their safety, permanence and utility and 
with flexibility to provide for possible future expansion. 
Two-lane highways should be designed so that passing of 
slower moving vehicles can be accomplished with ease and 
safety at practically all times. Divided highways should be 
designed as two separate one-way roads to take advantage 
of terrain and other conditions for safe and relaxed driv- 
ing, economy and pleasing appearance. All known features 
of safety and utility should be incorporated in each design 
to result in a National System of Interstate and Defense 
Highways which will be a credit to the Nation. 

These objectives can be realized by conscious attention 
in design to their attainment. All Interstate highways shall 
meet the following minimum standards. Higher values 
which represent desirable minimum values, a device used 
in previous Interstate standards, are not shown because it 
is expected that designs will generally be made to values 
as high as are commensurate with conditions, and values 
near the minimums herein will be used in design only 
where the use of higher values will result in excessive cost. 
In determination of all geometric features, including right 
of way, a generous factor of safety should be employed and 
unquestioned adequacy should be the criterion. All design 
features required to accommodate the traffic of the year 
1975 shall be provided in the initial design; however, 
where justifiable, the construction may be accomplished in 
stages. 

The Association Policy on Geometric Design of Rural 
Highways, the Policy on Arterial Highways in Urban 
Areas, when adopted, and the Standard Specifications for 
Highway Bridges shall be used as design guides where 
they do not conflict with these Standards. 


TRAFFIC BASIS 


Interstate highways shall be designed to serve safely and 
efficiently the volumes of passenger vehicles, buses and 


*To supersede the Design Standards for the National Sys- 
tem of Interstate Highways, adopted August 1, 1945. 


trucks, including tractor-trailer and semi-trailer combina- 
tions and corresponding military equipment, estimated to 
be that which will exist in 1975, including attracted, gen- 
erated and development traffic on the basis that the entire 
system is completed. 

The peak-hour traffic used as a basis for design shall be 
as high as the 30th highest hourly volume of the year 1975, 
hereafter referred to as the design hourly volume, “DHV 
(1975).” Unless otherwise specified, DHV is the total, two- 


direction volume of mixed traffic. 


RAILROAD CROSSINGS 


Railroad grade crossings shall be eliminated for all 
through traffic lanes. 


INTERSECTIONS 


All at-grade intersections of public highways and private 
driveways shall be eliminated, or the connecting road 
terminated, rerouted, or intercepted by frontage roads, ex- 
cept as otherwise provided under Control of Access. 


MEDIANS 


Medians in rural areas in flat and rolling topography 
shall be at least 36 feet wide. Medians in urban and moun- 
tainous areas shall be at least 16 feet wide. Narrower medi- 
ans may be provided in urban areas of high right-of-way 
cost, on long and costly bridges, and in rugged mountain- 
ous terrain, but no median shall be less than four feet wide. 

Curbs or other devices may be used where necessary to 
prevent traffic from crossing the median. 

Where continuous barrier curbs are used on narrow 
medians, such curbs shall be offset at least one foot from 
the edge of the through-traffic lane. Where vertical elements 
more than 12 inches high, other than abutments, piers, or 
walls, are located in a median, there shall be a lateral 
clearance of at least three and one-half feet from the edge 
of through traffic lane to the face of such element. 


BRIDGES AND OTHER STRUCTURES 


The following standards apply to Interstate highway 
bridges, overpasses and underpasses. Standards for cross- 
road overpasses and underpasses are to be those for the 
crossroad. 

Bridges and overpasses, preferably of deck construction, 
should be located to fit the overall alinement and profile of 
the highway. 

The clear height of structures shall be not less than 


Le 


14 feet over the entire roadway width, including the usable 
width of shoulders. Allowance should be made for any 
contemplated resurfacing. 

The width of all bridges, including grade separation 
structures, of a length of 150 feet or less between abutments 
or end supporting piers shall equal the full roadway width 
on the approaches, including the usable width of shoulders. 

Barrier curbs on bridges longer than 150 feet between 
abutments or end supporting piers and curbs on approach 
highways if used shall be offset at least two feet. Offsets to 


face of parapet or rail shall be at least three and one-half 
feet measured from edge of through-traffic lane and apply 
on right and left. 

The lateral clearance from the edge of through-traffic 
lanes to the face of walls or abutments and piers at under- 
passes shall be the usable shoulder width but not less than 
eight feet on the right and four and one-half feet on the left. 

A safety walk shall be provided in tunnels and on long- 
span structures on which the full approach roadway width, 
including shoulders, is not continued. 


Appendix B Notes for Underpasses and Overpasses on the Interstate System 


Tables 1 and 2 show the minimum dimensional require- 
ments for roadway shoulders, medians, and side clearances 
for bridges and underpasses as defined by the “Geometric 
Design Standards for the National System of Interstate 
and Defense Highways.” Where definition is not specifi- 
cally given in the Design Standards, the details presented 
here are the interpretation by the Bureau of Public Roads 
of the minimum acceptable dimensions. Vertical clearance 
in underpasses is 14 ft. plus paving allowance. 

Normally, the approach roadway dimensions are car- 
ried unchanged over short bridges and through under- 
passes, unless modification is required by the Design 
Standards, making desirable the continuation through 
structures of curbs, guardrails, and similar features of the 
approaches. 

Since safety walks are required on long bridges, this 
construction is shown with barrier curbs in Table 2, figures 
A2, B2, and D2. The median width in figure A2 may be 4 


ft. with a mountable curb, or 6 ft. with a barrier curb con- 


tinued from approaches. Where the barrier curb is intro- 
duced at the structure, the median width should be 8 ft. 

Figure El covers the left clearance requirement for ver- 
tical construction more than | ft. high in the median. 

Figure E2 shows the side clearance requirements for 
elevated structures with adjacent vertical construction. 

Left shoulders, W,, in figure Bl] may be carried on short 
bridges to continue approach shoulders, ranging in width 
from 2 ft. to 6 ft. Where the 6-ft. width is used, a barrier 
curb is not required on the structure if approaches have 
no median curb. For widths less than 6 ft., a barrier curb 
should be used on the structure. 

At the right shoulder of short bridges, see figures E3 and 
E4, the approach curbs at outer edge of shoulder and the 
guardrails should be carried on the structure without 
break in alignment. If the curb is introduced at the bridge, 
it may encroach | ft. 6 in. maximum on the shoulder width 
in order to continue the approach guardrail alignment. 

In those cases where no barrier curbs are provided, 


TABLE 1. WIDTHS AT UNDERPASSES ON INTERSTATE HIGHWAYS 


TYPE OF UNDERPASSING 
HIGHWAY 


=== 
- 
~~ 


FOUR-LANE DIVIDED 
A HIGHWAY 


Wide median 


FOUR-LANE DIVIDED 
B HIGHWAY 


Narrow median 


ROADWAY ELEMENTS 
THROUGH STRUCTURES 


Alternate piers* 


are 


TWO-LANE DIVIDED 
Cc as first stage 


Ultimate four-lane divided 
highway 


TWO-LANE ONE-WAY 
HIGHWAY 


*Alternate for cases where 
single pier in median is not 
practicable. 


**The 10-ft. right shoulder 
is the normal minimum, which 
may be reduced to 8-ft. side 
clearance where approach 
shoulders are less than 10 ft., 
as in rugged mountain terrain. 


ee ee 
Lt 2a RE 
385! 


The left or median clearance 
dimension, 4.5 ft., may not be 
reduced. 


19 


bridge rails shall be designed to resist a lateral force of 
not less than 500 lb. per lin.ft. applied to the lower rail. 
Where a single beam-type rail is provided, it shall be de- 
signed to resist the force of 500 lb. per lin.ft. applied to 
the center of the rail. 

Where auxiliary lanes come on bridges, a curb will be 


TABLE 2. WIDTHS AT OVERPASSES ON INTERSTATE HIGHWAYS 


TYPE OF OVERPASS 
HIGHWAY 


FOUR-LANE DIVIDED 
HIGHWAY 
Single structure, 
narrow median 


FOUR-LANE DIVIDED 
HIGHWAY 
Double structure, 
wide median 


FOUR-LANE DIVIDED 
HIGHWAY 


used with railing offset 1 ft. 6 in. on right and left. In the 
length of auxiliary lane where the width is less than 12 ft., 
the curb is offset 2 ft. when introduced at the bridge. On 
short bridges where the tapered auxiliary lanes come into 
the right shoulder width, normal shoulder dimensions 
govern as shown in figure E4. 


ROADWAY WIDTHS ON STRUCTURES 


SHORT STRUCTURES 


LONG STRUCTURES 


Wide median 
with approach curbs 


TWO- WAY 
») HIGHWAY 


Narrow median 
silat 3.5) 


Viaduct or bridge 


® S j.face of column 


SIDE CLEARANCE FOR 
MULTIPLE-LEVEL STRUCTURE 


Same as B2 


Full width |. Face of approach 
shoulder guardrail 


Continuous curb Approach curb 


Face of approach 
1.5'| max. guardrail 


Curb carried beyond 
structure and returned 
@ back of guardrail 


RIGHT SHOULDER 


*The 10-ft. right shoulder is the normal minimum, which may be reduced to 6 ft. to suit approach shoulders in rugged moun- 


tain terrain. 


Note: C is the left curb offset in the median: C=0 for mountable curbs; C =1 ft. for continuous barrier curbs; C =2 ft. for 


introduced barrier curbs. 


W, is the left shoulder width, used only on short bridges. The maximum width recommended for four-lane bridges is 6 ft. 
Wider shoulders may be considered for six- and eight-lane bridges. 


Appendix C Widths at Underpasses and Overpasses Not on the Interstate System* 


TABLE 3. WIDTHS AT UNDERPASSES ON NON-INTERSTATE HIGHWAYS 


** 
ROADWAY ELEMENTS THROUGH STRUCTURES | ynpeRpass.IN FT 


TYPE OF UNDERPASSING 
HIGH WAY DOUBLE t 
SINGLE OPENINGS DOUBLE OPENINGS OPENING OPENING 
| Min. { Des. | Min. | Des. 


FOUR-LANE DIVIDED 32 42 
HIGHWAY (68) | (88) 
[24 
MAJOR TWO-LANE 
HIGHWAY 
as first stage 70 SS a 
Ultimate divided : 6 
highway ; 
MAJOR TWO- OR 
THREE-LANE HIGHWAY 
Widened through structure 70 
and interchange area 


en 


op i 


MAJOR TWO-LANE 
HIGHWAY 
D Provision for 
possible future 
improvement 


TWO-LANE HIGHWAY 
No foreseeable 
E P 34 
improvement 
in type 6) ree = 16 
LOCAL ROAD fea 
F Narrow two-lane or 28 34 
one-lane width 4| 20' Ia 
6 6 


*From A Policy on Geometric Design of Rural Highways, American Association of State Highway Officials, 1954. 
**Upper set of dimensions, minimum; lower set of dimensions, desirable. Exclusive of auxiliary lanes and sidewalks. 


+Value in parentheses is total width of underpass for two spans. 


2] 


ee 


TABLE 4. WIDTHS AT OVERPASSES ON NON-INTERSTATE HIGHWAYS 


* 
chi ras Ke tote ts ROADWAY WIDTHS ON STRUCTURES 


HIGHWAY SHORT STRUCTURES LONG STRUCTURES 


FOUR-LANE DIVIDED 
HIGHWAY 


Single structure 


FOUR-LANE DIVIDED 
HIGHWAY 


Double structure 


MAJOR TWO- OR 
THREE-LANE HIGHWAY 
Widened over structure 

and interchange area 


MAJOR TWO-LANE 
HIGHWAY 


TWO-LANE HIGHWAY 
(Local character) 


LOCAL ROAD Pvt.t+ 4' 
Narrow two-lane or | | 


one -lane width 


*Exclusive of auxiliary lanes and sidewalks. 
Overall width, face of rail to face of rail: add 3 ft. minimum to roadway widths. 
Upper set of dimensions, minimum; lower set of dimensions, desirable. 


Back Cover—This attractive bridge at the junction of Routes 90 and 35, 
near Des Moines, Iowa, was one of the first to be built on the Interstate 
System. The use of precast-prestressed beams ensured speed of construction. 


Printed in U.S.A. T 34 


ee 


‘ 


RAN 


Ss ta nt 


s Blast-Resistant 
Concrete Houses 


Ta. DESIGN CONSIDERATIONS 
4 ee | 
3000 4000 
Dis 


PORTLAND CEMENT ASSOCIATION 


33 WEST GRAND AVENUE 
CHICAGO 10, ILLINOIS 


Ny 


Center of explosion 


Initial shock front 


Rag e 
/aQ/ Uistan 
Ce 


Ground zero distance, d ae) 


Blast-Resistant Concrete Houses 


Design Considerations 


Introduction 


Extensive investigations and tests show that it is possible to 
design and build houses to withstand pressures from nuclear 
blast. Concrete construction will give protection with only little 
additional cost and without sacrificing the function or appear- 
ance of a home. 

This publication presents a simplified description of blast 
loading as it affects one-story houses” in order to provide a 
clear understanding of the fundamental problems involved. 


Shock Wave and Reflected Pressure 


When a nuclear bomb explodes above ground, a shock wave 


*Data in this publication are based on studies made for the Portland 
Cement Association by Ammann & Whitney, consulting engineers, 
New York and Milwaukee; and Ellery Husted of Gugler, Kimball and 
Husted, architects, New York. Both consultants have had extensive 
experience with various governmental agencies in the field of blast- 
resistant construction and the effects of nuclear weapons. 


Reflected shock front 


Height of burst, h 


Rag . 
/o/ Liston 
Cc 


of decreasing intensity leaves the center of explosion with an 
initial speed several times the speed of sound (15,000 ft. per 
second at | breakaway'’) and travels outward with a diminish- 
ing velocity that approaches the normal speed of sound of 
1,100 ft. per second. Fig. 1 shows the location of the shock 
front after a certain interval of time and its relationship to the 
structure. The distance between the structure and the center of 
explosion is determined by the height of burst above ground, 
h, and by the distance, d, from ground zero, the point directly 
below the center of explosion. 

The shock front, which presents a rapidly expanding spheri- 
cal surface, is characterized by an abrupt increase in pressure. 
The intensity and duration of this pressure can be predicted 
quite accurately if no interference to the shock front occurs. 

Because a bomb is detonated above ground, a reflected 
shock front develops. The reflected wave, as indicated in Fig. 1, 
adds to the intensity of the initial shock front. At some distance 


Initial shock front 


Ground zero distance, d 


Fig. 1. Geometric relationship between center of 
explosion, shock front and structure. 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, t 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold ¢ 
of the Association and its varied services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, aa 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on 


| 
Copyright 1956 by Portland Cement Ass: 
| 


the two shock fronts fuse together near the ground, as shown 
in Fig. 2. The height of this fused shock front increases as it 
moves outward. The front is approximately vertical and sweeps 
over the surrounding area with an intensity corresponding to 
a bomb of twice the yield of the actual one. The pressure in 
the combined shock wave is generally referred to as the 
side-on pressure and is denoted as p,. Its intensity is dependent 
on distance from ground zero, height of burst and bomb yield. 

As the shock front moves forward, the peak side-on pres- 
sure, denoted as p%, decreases as indicated by the dash line 
in Fig. 3. For a 20-KT* bomb, such as that dropped on Hiro- 
shima, the peak side-on pressure at ground zero is about 
three and one-half times the atmospheric pressure, 14.7 psi; 
at 2,000 ft. from ground zero it reduces to about 24 psi; and 
at 9,000 ft. it is, approximately, one-sixth the atmospheric 
pressure. 

For a constant ratio of h to d the distance at which the 
peak side-on pressure exerted by any other bomb size is 
approximately equal to the pressure exerted by a 20-KT bomb 
at a distance d, is given by the hydrodynamical equation 


3 
W 
d=dha|—— 
20 


d=the horizontal distance from ground 
zero for a bomb W; 


in which 


d, =the horizontal distance from ground 
zero for a nominal bomb; 
W=~yield of the bomb in KT. 
For example, the pressure exerted by a 160-KT bomb at a 


*Kiloton or 1,000 tons. A 20-KT bomb, which has roughly the effec- 
tive energy release of 20,000 tons of TNT, is considered nominal. 


Reflected shock front 56 


BSS 
@ 


distance of faa yy = 2h is the same as the pressure 
exerted by a 20-KT bomb at the distance d,. 

The distribution of pressure behind the fused shock front 
at two different distances is plotted in Fig. 3 as solid lines under 
the dash line. In these cases the pressure decreases from the 
peak side-on value at the designated point to a total less than 
atmospheric pressure at some distance behind. As the shock 
wave travels outward, the distance, d,, subjected to positive 
pressures increases and the peak intensity decreases. 

The pressure conditions that exist when a blast hits a build- 
ing are indicated in Figs. 4 and 5. The pressure on the front 
wall facing the blast builds up because of interference with 
the forward movement of the shock front. This might be de- 
scribed as a piling up of energy. The intensity of the shock 
wave reflected from the front wall depends on the initial side- 
on pressure, the width and height of the wall and the angle of 
incidence measured as the angle between the direction of the 
blast wave and the normal to the wall surface. Under very 
unfavorable conditions the reflected pressure could be as much 
as four or more times the side-on pressure. This build-up of 
pressure applies mainly to the lateral forces that act on the 
wall facing the blast. 

Near the top of the wall the reflected shock wave travels 
upward and causes turbulence over the roof. At the front edge 
of the roof the vertical pressure is approximately the same as 
the initial side-on pressure. Beyond the edge, however, the 
pressure drops to a value far below p,. At a horizontal dis- 
tance about three times the height of the wall, the turbulence 
decreases and the pressure again approaches p,. A similar 
but much smaller effect takes place near the rear edge of the 
roof. 


Initial shock front 


-KT bomb 


§ 


Peak side-on pressure at shock front when 
height of burst is 2000 ft above ground. 
lt eee: 


Fused shock front 


<—__ ——— 24 
Toward center Blast 
of explosion movement 


@ 


Side-on pressure, p,,in psi due toa 20 


Fig. 2. Formation of a fused shock front. 


— 
—| 


Fig. 3. Peak pressure on the ground as a function 
5 -8 
i for a nominal ) | 2 3 4 5 6 rd 8 9 Te) il 
Boece toded Elias pan ground Distance in lOOO ft. from ground zero 
/ . . 


Shock front 


_—_—_—_——————— 
Blast 
movement 


Fig. 4. Blast load on a partially engulfed building. 


After the shock front has passed the building, a pressure 
builds up on the rear wall that, at its maximum, is slightly less 
than the value of p,, as indicated in Fig. 5. 

The great variety of pressures that may exist around a 
building, all varying with time, are derived from the initial 
side-on pressure. They also depend on intensity and duration 
of blast and on the size, shape and orientation of the structure. 


Duration of Peak Pressure 


As pointed out in connection with Fig. 3, the side-on pressures 
immediately behind the shock front decrease. Therefore, in 
contrast to ordinary static loads, the pressures exerted on a 
building decrease with time, as shown in Fig. 6. As the blast 
moves by the building, it goes through a positive phase in 
which the pressures are greater than atmospheric pressure. 
After a relatively short time, the blast enters a negative phase 
of longer duration which, because of its lower intensity, is 
frequently disregarded in design. The change in pressure dur- 
ing the positive phase may be approximated roughly with a 
straight line. The time, f,, is the duration of the positive phase 
of the blast load, which for a nominal bomb will vary from 
Y2 to 1 second, depending on the distance of the structure 
from the bomb. 

This rather simple pressure-time relationship is complicated 
by the previously described build-up of shorter-duration re- 
flected pressures on the front face of the front wall and by 
pressures that exist on the inside face of the wall. Actually, 
the positive phase of blast pressures cannot be represented 
by a single straight line. An idealized pressure-time diagram 
for a front wall located at the distances under consideration 
is approximated in Fig. 7 by two straight lines. It consists of a 


Shock front 


—_—_——_> 
Blast 
movement 


Fig. 5. Blast load on a fully engulfed building. 


Pressure,p, 


~___ - eee 


Time 


Fig. 6. Pressure-time curve at a given location. 


short-duration peak load followed by a smaller drag load of 
longer duration. Peak load includes reflected side-on pres- 
sures. Its duration, t,, is dependent primarily on the time it 
takes for a wave to travel three times the height of the wall 
or one and one-half times its unbroken width, whichever is 
smaller, at a speed approximately that of normal sound travel. 
For this reason the duration of peak-load pressures is very 
sensitive to the geometry of the building. The lower straight 
line represents the effect of drag on the structure. The total 
duration of loadings is approximately f,, but from a strength 
consideration of the panels, the critical duration is dependent 
mainly on t,. 

For extremely narrow members such as poles and free- 
standing columns, the duration of reflected pressures, as shown 
in Fig. 8, is sharply reduced as compared with the longer dura- 
tion shown in Fig. 7. The duration, t,, is so short that the effect 
of the peak load is negligible and the critical loading is due to 
drag. 


Blast Load on a Structure 


Even if all necessary data were available for the calculation 
of the blast load exerted on a building with openings, such a 
determination would not be warranted in the case of small 
buildings because of the number of variables involved. How- 
ever, a qualitative understanding of the effect of openings 
can be gathered from test observations. 

In the nuclear explosion at the Yucca Flat, Nev., testing 
ground on May 6, 1955, four houses of reinforced concrete 


Time at max. 
deflection 


Peak load 


Pressure,p, 


GG!" 


LL. 


tr 


Fig. 7. Simplified pressure-time curve for members of large 
width and height. 


Short-duration peak load 


Time at max. 
deflection 


Pressure, py 


Fig. 8. Simplified pressure-time curve for members of nar- 
row width. 


were exposed to blast pressures. The houses were constructed 
in accordance with ordinary requirements for earthquake re- 
sistance.* Two were located 4,700 ft. and two at 10,500 ft. 
from ground zero. At 4,700 ft. one house of reinforced con- 
crete masonry and another of precast lightweight reinforced 
concrete withstood the blast of a 35-KT bomb, exploded at a 
height of 500 ft. The equivalent distance from ground zero in 
the case of a nominal bomb exploded 2,000 ft. above ground 
can be shown to be approximately 6,000 ft.** The minimum 
safe distance for a windowless house can be shown by theoreti- 
cal investigations to be approximately 11,000 ft. The decrease 
in safe distance, as proven by the test, can be credited to the 
relieving effect of wall openings and to the orientation of the 
structure. These effects are illustrated in Fig. 9. 

If a wall is placed parallel to the blast, as shown in Fig. 9(a), 
it will get very little unbalanced load. The pressure merely 
engulfs it and is in equilibrium at any time. When a wall is 
perpendicular to the blast, as in Fig. 9(b), the reflected pres- 
sures, p,, on the front face will build up from two to more than 
four times! the value of the side-on pressure, p,. If a wall has 
windows, the shock front enters and immediately begins to 
exert pressure on the back of the wall, as shown in Fig. 9(c). 
The net load on the wall is equal to the difference in load on 
the two sides. 

The duration of the peak pressure on a windowless structure 
usually will be relatively long since large, unbroken wall areas 
slow down the escape of reflected pressure. The strength of 
the front wall of a windowless house must be adequate to resist 
the peak load, as shown in Fig. 7. 

A house with large window areas has a different type of 
loading curve. After the windows are blown in and only piers 
and spandrels remain, a quick escape of the reflected pres- 
sures is possible. In extreme cases only the drag part of the 


*Uniform Building Code by Pacific Coast Building Officials Con- 
ference. 

The increased safe distance is necessary primarily because of the 
greater spread of pressure at increased height. 

{See "Design of Blast Resistant Construction for Atomic Explosions” 
by C. S. Whitney, B. G. Anderson, and E. Cohen, ACI Proceedings, 
Vol. 51, page 607, Fig. A1.5. 


—_— 
Blast 
movement 


Shock front 


—_—_——_ 
(a) Blast 
movement 
—_—_—— 
Blast = 
movement 


Shock front 


Shock front 


(b) (c) 


Fig. 9. Pressure on walls of different configurations. 


load diagram shown in Fig. 8 will be effective as load on the 
structure. The condition encountered in one-story houses is 
somewhere between the two extremes. 


General Layout 


Except in those areas in which full protection against blast is 
required, the house should be laid out in such a way that it will 
pick up as little of the blast load as possible. Walls without 
structural function should be made friable, that is, capable of 
collapsing under the impact of a shock wave without trans- 
mitting more than a negligible part of the load to the structural 
frame. In this category belong light and brittle curtain walls, 
and ordinary doors and windows. 

In many cases the blast direction can be predicted. In a 
suburb the direction is usually toward an industrial area or 
the city center. The main structural walls should preferably 
be made parallel to the blast direction and all other walls 
should be provided with large windows. The side-on pressures 
would then tend to equalize each other on the two faces of the 
structural walls. Openings in these should be kept to a mini- 
mum to provide maximum strength. 

If the blast direction is not known, a wall may be subject to 
either full lateral reflected pressures for a blast normal to it, 
or to shear and smaller lateral pressures for a blast parallel 
with it. Openings would decrease the duration of lateral pres- 
sures but would reduce both the shearing and bending strength 
of the wall. Under such conditions the best solution is to make 
all wall elements uniform in width between openings. 

If blast enters a house through openings, interior walls may 
also be exposed to large pressures. If they have a structural 


Fig. 10. One-story blast-resistant house. 


function, they should be designed and built in a manner similar 
to exterior walls. To limit the maximum unbroken wall area 
for interior walls is even more important than for exterior 
walls, since no escape of reflected pressure is possible at 
roof level. 

It is generally advisable to provide approximately the same 
amount of structural walls in each direction of a building. For 
illustration, a long, narrow building normally should have 
longitudinal walls broken up by large windows and have only 
small openings in transverse walls. The center of gravity of 
the resistance from all shear walls should coincide as closely 
as possible with the center of gravity of the total load, in 
order to avoid twisting of the building. In some cases a rigid 
concrete frame around a large opening may be necessary 
for additional strength. 

If the house has many openings, the roof will get only a 
relatively small unbalanced load. It is not desirable, in gen- 
eral, to let the blast reach the basement. Therefore, the floor 
slab for average conditions would have to be designed for 
approximately full side-on pressure. If the basement is to be 
used as a shelter, that portion of the floor over the shelter 
should be designed for even higher pressures. 

Special consideration should be given to layouts that may 
trap the blast inside the building. This condition would exist, 
for example, where three solid walls form a U with the open 
side against the blast. High reflected pressures may occur in 
such cases against not only the walls but also the floor and 


roof. The resulting net upward pressure could result in uplift 
of the roof if it were not properly tied down. 


Details of a Blast-Resistant House 


Important blast-resistant features are incorporated in the de- 
sign details of a one-story modern house with basement as 
shown in Figs. 10, 11 and 12. This house was designed to resist 
blast at 9,000 ft. from a nominal bomb exploded 2,000 ft. 
above ground, with the assumption that there is no relief as a 
result of pressures entering the windows. Because of the large 
window openings, the house will actually withstand larger 
pressures than those calculated. No restrictions are imposed 
on orientation. 

The exterior walls of heights suitable for conventional one- 
story houses are of 12-in. concrete masonry, as shown in 
Fig. 11. Concealed behind the furring are vertical tierods— 
No. 7 bars at 24-in. spacing—securely anchored to the roof 
and the floor. As the wall bends under lateral pressure, it Is 
compressed between the two slabs, which are restrained from 
moving apart by the tierods (see Fig. 13). The wall acts as a 
vertical beam with fixed ends subject to an axial load and 
supported at the roof and floor level. It is capable of resisting 
pressure from either direction. 

The 6-in. reinforced concrete roof slab is designed to with- 
stand the vertical side-on pressures; it also acts as a deep 
horizontal girder that transmits horizontal reactions from the 
front wall to the side walls. The advantage of a flat roof is — 


twofold: (1) by decreasing the height of the building it reduces 
the total area exposed to reflected pressure; (2) with a strong, 
flat concrete roof the walls exposed to blast act as beams sup- 
ported both top and bottom, whereas without such roof con- 
struction, the walls would act as cantilevers and have much 
less resistance. 

Side walls act as shear walls that resist the horizontal re- 
actions from the roof. For this reason, as shown in Fig. 12, 
ample bracing has been provided by walls in both directions. 

The 6-in. reinforced concrete floor slab is able to withstand 
a blast pressure of 360 psf. A shelter area is provided in the 
basement for protection of the occupants. In that portion of 
the floor over the shelter, the slab thickness and the reinforce- 
ment remain the same, but the span is reduced to approxi- 
mately 3 ft., which makes the slab safe for a blast pressure of 
1,900 psf. 

Blast resistance of a windowless house can be predicted 
accurately by means of a dynamic analysis. Windows com- 
plicate the design because they reduce the duration of the 
load on walls facing the blast. The following equation can be 
used to estimate the increase in blast resistance of the 12-in. 


wall when provided with windows and openings spaced not 
more than 18 ft. and not less than 2 ft. apart: 
d=" 300195), 


6" reinforced 
concrete roof 


\2" concrete 
masonry units 


Vertical bar threaded 
at both ends 


Furred-out plaster 


6" reinforced 
concrete floor ~ 


Grade line 


| _—Portland cement 
Horizontal plaster 


reinforcement 


Fig. 11. Details of a reinforced concrete masonry wall. 


BEDROOM 
14-0"x 12'-0" 


WORKSHOP 
14-0"x 13'-0" 


LIVING = DINING 
23-0" 13-0" 


GARAGE 
10-0"x 20-0' | | 


BEDROOM 
14'-0"x 12-0" 


Fig. 12. Floor plans for a one-story blast-resistant house. 


where d, is the safe distance in feet from ground zero and b 
is the width in feet between adjacent openings. 

For a windowless structure the maximum value of b=18 ft. 
should be used. The formula then gives d, equal to 9,450 ft. 
If the relief obtained by windows is taken into account and a 
6-ft. width of wall between openings is assumed, minimum safe 
distance for the front wall is 

d, = 350 (9+6) = 5,250 ft. 

For an 8-in. concrete masonry wall, the pressure that can be 
resisted is reduced in proportion to its thickness. For example, 
the peak side-on pressure for a 12-in. concrete masonry wall 
without openings at the safe distance of 9,450 ft. is, from 
Fig. 3, 2.5 psi. An 8-in. wall can therefore resist a peak side-on 


pressure of 2.5 5=1.65 psi, which is the pressure at a dis- 


tance of 11,000 ft. Therefore, an 8-in. wall at 11,000 ft. will 
withstand the same blast that a 12-in. wall will resist at 9,450 ft. 

To estimate the blast resistance of the concrete masonry 
test house at Yucca Flat, referred to on page 5, assume that a 
12-in. wall has a width between openings of 5 ft. The minimum 
safe distance is 

d, = 350 (9+5) = 4,900 ft. 

At this distance the peak side-on pressure is 7.8 psi for a 

nominal bomb at 2,000-ft. altitude. For an 8-in. wall this value 


is reduced to 7.8X 5 =5.20 psi, which corresponds to a safe 


distance from ground zero of 6,400 ft. This compares favor- 
ably with the value given on page 5, which was calculated by 
converting the side-on pressure for the actual bomb size and 
height of explosion used in the test to that of a nominal bomb 
exploded at 2,000 ft. above ground. 


Design Aids 


The two load charts, Figs. 14 and 15, may be used to design 
roof and floor slabs. They give the thickness and reinforce- 
ment for a reinforced concrete slab for different spans at 
various distances from ground zero of a 20-KT bomb. The 


BASEMENT PLAN 


BASIC PRINCIPLES OF AITR-ENTRAINED CONCRETE 


By William Lerch 


Table of Contents 


Page 
1. Introduction a 
2. Air-Entraining Materials 2 
3. The Nature of Air-Entrained Concrete 3 
4. Specifications for Air-Entraining Cements 3 
5. Air-Entraining Cements Vs. Air-Entraining Admixtures 4 
6. Methods of Measuring the Air Content of Freshly- 4 
Mixed Concrete 

7. Design of Mixes 5 

8. Laboratory Methods of Test for Surface Scaling and 6 
Resistance to Freezing and Thawing 

9. Resistance of Air-Entrained Concrete to Surface | 6 
Scaling 

10. Resistance of Air-Entrained Concrete to Freezing 8 

and Thawing 

11. Resistance of Air-Entrained Concrete to D-Cracking 9 

12. Strength of Air-Entrained Concrete 10 

13. Bond between Concrete and Steel Le 

14. Sulfate Resistance of Air-Entrained Concrete 11 

15. Abrasion Resistance of Air-Entrained Concrete 1d 

16. Permeability of Air-Entrained Concrete ig 

17. Air-Entrained Concrete in the Production of a 

Concrete Pipe and Block 

18. Blends of Portland Cement with Natural Cement 13 

19. Coloring Agents - Their Effect on Air Content 14 

and Durability 

20. Effect of Mix Proportions and Aggregate 14 

Gradation on the Air Content of Concrete 
21. Effect of Slump and Vibration on the Air Content 16 


of Concrete 


22. Effect of Temperature on the Air Content of Concrete 16 


23. Effect of Mixing Time on Air Content of Concrete Li? 

24. Effect of Percentage of Sand on the Air Content L7 
of Concrete 

25. Concluding Remarks ake 

26. References 19 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, fe‘ 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold pri 
of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, enga 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on re 


Copyright 1954 by Portland Cement Association 


BASIC PRINCIPLES OF AIR-ENTRAINED CONCRETE 


By William Lerch* 


-o00- 


INTRODUCTION 


The application of salts or granular materials mixed with 
salts on concrete pavements, a practice that was initiated about 
1930, was accompanied by a new type of surface scaling on the pave- 
ments that had not been observed previously. Field surveys clearly 
disclosed that the surface scaling was caused by the application of 
salt and not by any change in the characteristics of the cement or 
the quality of the concrete. The scaling occurred at intersections 
and on curves and grades where salts were applied. It did not occur 
on long intervening sections where salts were not applied. 


The field surveys also disclosed that oil dripping from 
cars partially or completely prevented the surface scaling on some 
parts of the pavement. This led to early studies of the applica- 
tion of oils on the surface of the concrete as one means of prevent- 
ing the surface scaling. It was found thet the application of oils 
did have some merit. The method and suitable time of surface treat- 
ment with oil provided some difficulties. The oils did not complete- 
ly or permanently prevent the surface scaling. 


The Research Laboratories of the Portland Cement Associa- 
tion initiated studies of air-entrained concrete in 1937. These 
studies were part of a comprehensive program of research to find a 
means of preventing the surface scaling that occurs on non-air- 
entrained concrete pavements when salts (calcium chloride or sodium 
chloride), or granular materials mixed with salts, are applied for 
ice removal. The laboratory studies showed very promising results. 
The Association then obtained the cooperation of the Bureau of 
Public Roads and State Highway Departments to participate in the 
construction of experimental roads to test air-entrained concrete 
in pavements under field service conditions. The first experimental 
project was constructed in Nassau County, N. Y. in 1938. Addi- 
tional and larger projects were constructed in following years. The 
performance of the slabs constructed with air-entraining portland 
cements was so outstanding on thes2 early experimental projects that 
when plans were being made for the Long-Time Study of Cement Per- 
formance in Concrete the Advisory Committee recommended that six air- 
entraining cements should be included in the program. In 1942 the 
ASTM adopted a tentative specification for air-entraining portland 
cement, ©175-42T. 


* Head, Performance Tests Group, Research and Development 
Laboratories, Portland Cement Association, Chicago, Illinois. 


Fig. 1 shows a typical example of the type of surface 
scaling that is caused by the application of salts tat oe removal 
and the beneficial effect of air}entrained concrete - The lane 
at the left was made with a non-air-entraining cement and shows bad 
surface scaling after two winters. The lane at the right was made 
with an air-entraining cement and is in excellent condition after 
seven winters, Fig. 1A. Laboratory studies and field experience 
have consistently shown that purposely entrained air vastly increases 
the resistance of concrete to disintegration by frost action and to 
scaling by the direct application of salts for ice or snow removal. 


Air-entrained concrete has been used successfully in pave- 
ments in the northern states, where severe frost action is encoun- 
tered, for about 14 years. With the advent of its use in pavements, 
it was found that air-entrained concrete has many beneficial prop- 
erties that would prove advantageous in other types of construction. 
They more than offset any reduction in strength that may occur. The 
beneficial properties ares an increase in workability and cohesive- 
ness, a reduction in segregation and bleeding tendency, and increased 
resistance to the aggressive action of sulfate waters. These prop- 
erties all tend to produce a more homogeneous and more durable con- 
crete, and better appearing structures. Air-entrained concrete is 
now being used extensively in pavements and its use in other types 
of construction is increasing rapidly. It is being used in prac- 
tically every type of construction where cement is used. 


The continuously increasing use of air-entrained concrete 
has raised many new questions that have required further study. 
This paper describes some of the more significant results obtained 
from these studies. 


AIR-ENTRAINING MATERIALS 


There are a large number of materials that can be used as 
air-entraining agents to produce air-entrained concrete. They in- 
clude the following general types of materials: 


(1) Natural wood resins, such as rosin, 

(2) Animal or vegetable fats and oils such as tallow, 
fish oil and their fatty acids, such as stearic 
and oleic acid, 

(3) Various wetting agents such as alkali salts of 
sulfated and sulfonated organic compounds, 

(4) Water-soluble soaps of resin acids and animal 
and vegetable fatty acids, 

(5) Miscellaneous materials such as sodium salts of 
petroleum sulfonic acids, hydrogen peroxide, 
aluminum powder, etc. 


Introduction of the air-entraining agents into the con- 
crete can be accomplished in two ways —- by intergrinding with the 
cement clinker, or by adding directly to the concrete materials at 
the mixer. The ASTM has a Tentative Specification for Air-Entrain- 
ing Additions for Use in the Manufacture of Air-Entraining Port- 
land Cement, C226; and a Tentative Method of Testing Air-Entraining 
Admixtures for Concrete, 0233. Materials meeting the requirements 
of these specifications are acceptable. 


* Numbers in parentheses refer to references appended to this paper. 


* 2% 


THE NATURE OF ATR-ENTRAIN&ED CONCRETE 


Air-entraining agents, even when used in very small 
quantities (0.01 to 0.05 per cent by weight of the cement), have 
the power of introducing into the concrete a larger amount of air 
than is found in the usual concrete. Fig. 2 shows the size and 
distribution of the bubbles as observe Woe the microscope and 
reproduced by the Camera Lucida method\ » @ method that has veen 
used to determine the air content of hardened concrete. Unlike the 
air in the usual concrete, this intentionally entrained air appears 
to exist in the form of minute, disconnected bubbles well distrib- 
uted through the mass. These air buobles vary in size over a range 
of from a few microns up to about 75 microns in diameter. The nun- 
ber of bubbles in a unit volume may be estimated from the deter- 
mined air content of the concrete and the corresponding average 
diameter of the bubbles, assuming that the bubbles are true spheres. 
Calculations of this type indicate that as many as 400 to 600 
billion bubbles are entrained in a single cu. yd. of concrete hav- 
ing an air content in the range of 3 to 6 per cent by volume. 


The linear traverse technique(2) provides another and more 
rapid method for determining the air content of hardened concrete. 


The presence of these tiny bubbles materially alters the 
properties of both the plastic mixture and the hardened concrete. 
The air bubbles serve as reservoirs that accommodate the expansion 
resulting from the freezing of water within the concrete. As the 
freezing of the water within the capillaries progresses, the ex- 
pansion pressure is relieved by forcing the excess water into the 
air bubbles where the expansion during freezing can occur without 
disrupting the concrete. When thawing occurs the air compressed 
in the pubbles and capillary forces cause the water to move back 
into the capillaries. Thus the poubdbles continue to serve their 
purpose during repeated cycles of freezing and thawing. 


SPECIFICATIONS FOR AIR-ENTRAINING CEMENTS 


Current ASTM Tentative Specifications for Air-Entrain- 
ing Portland Cements provide for three types of air-entraining 
portland cement - Types IA, IIA and IIIA - and a Tentative Speci- 
fication for Air-Entraining Portland Blast-Furnace Slag Cement. 
These specifications permit intergrinding the air-entraining 
agents in the amount required to produce an air content of 18+3 
per cent in a 1-4 standard Ottawa sand mortar when tested in ac- 
cordance with ASTM C185. The air-entraining agent interground 
with the clinker must meet the requirements of the ASTM Tentative 
Specifications for Air-Entraining Additions for Use in the Manu- 
facture of Air-Entraining Portland Cement, C226. 


In Specification C175-44T which first used the test of 
1-4 standard Ottawasand mortar for controlling the air-entraining 
capacity of the cement, the limits on the air content of the mor- 
tar were placed at 14+4 per cent. It was found that cements giv- 
ing air contents in the lower range by the mortar test would give 
low air contents in concrete. In 1947 Specification 0175-47T was 
changed to place the limits at 18+3 per cent in the mortar test 
and these same limits were retained in 0175-51T. It appears that 
cements meeting this requirement will usually entrain the proper 
amount of air in the concrete. 


* 3% 


AIR-ENTRAINING CEMENTS VS. AIR-ENTRAINING ADMIXTURES 


The first question to be answered, following a decision 
to use air-entrained concrete, is whether to use an air-entraining 
cement or an air-entraining admixture. Each method has its ad- 
vantages and disadvantages. 


A given air-entraining cement contains a fixed amount of 
air-entraining agent which determines the amount of air that will 
be entrained in the concrete. The air content can be varied some- 
what by making adjustments in one or more of the variables that 
influence air content, provided, of course, such adjustments do 
not violate any of the provisions of the pasic specifications. The 
variables that affect the air content of the concrete will be dis- 
cussed later. 


When air-entraining admixtures are used the quantity of 
air in the concrete can be adjusted from time to time during the 
progress of the work, as changing conditions require. Continuous 
supervision is required to give assurance that the proper quantity 
of air is obtained at all times. 


Many engineers favor the use of air-entraining cement 
because in this way they avoid the necessity of adding a fifth in- 
gredient at the mixer. They stress the practical problems which 
are involved in the accurate control on the job of adding small 
amounts of such active materials as air-entraining agents. More- 
over, additions at the mixer require either the installation of some 
automatic dispensing device or the service of a workman, with the 
ever-present hazard of mistakes due to the mechanical or human ele-— 
ment. The use of air-entraining cement avoids these difficulties. 
The use of an air-entraining cement, meeting the requirements of 
ASTM specifications, or an air-entraining addition, does not always 
insure that concrete will have satisfactory air-entraining charac- 
teristics. Under certain known and special circumstances depar- 
tures from normal air expectancy may occur. Tests for air content, 
both preliminary to construction and routine tests for control pur- 
poses during construction, should be required regardless of which 
method of entraining air is employed. The amount of air which will 
be entrained in the concrete cannot be left to chance. 


METHODS OF MEASURING THE ATR CONTENT OF FRESHLY-MIXED CONCRETE 


There are three current methods for measuring the air 
content of freshly-mixed concrete. They are: 


(1) The gravimetric method 
(2) The pressure method, and 
(3) The volumetric method. 


In the gravimetric method (ASTM Designation C138), the 
sum of the absolute volumes of the ingredients in a known volume 
of concrete is calculated and subtracted from the known volume, 
the difference being taken as the volume of air in the concrete. 
This method requires accurate information on the specific grav- 
ities of the cement and aggregates and the absorption of the 
aggregate. It also requires a sensitive weighing scale which is 
difficult to transport and maintain under job conditions. 


* 4 * 


With the pressure method (ASTM Designation C231), the 
volume of air is measured indirectly by the change in volume it 
undergoes when subjected to a known pressure. It is based on 
Boyle's Law, that the volume of a gas (at a given temperature) is 
inversely proportional ny the pressure to which it is subjected. 
Messrs. Klein and Walker(3) first used the pressure method. 
Menzel(4,5) made a further study of the method and described 
methods for calibrating the apparatus and procedures for obtain- 
ing the aggregate correction factor, that is, a correction for the 
air contained within the aggregate which would also be compressed 
during the test. Fig. 3 shows a photograph of equipment for meas- 
uring the air content of freshly-mixed concrete by the pressure 
method. 


With the volumetric method the volume of air is measured 
directly. It is suitable for use with all types of aggregate and 
is especially recommended for use with concrete containing highly 
porous aggregates such as expanded slag, burned shale, etc. With 
this type of aggregate it is difficult to obtain the specific grav- 
ity to the degree of accuracy required by the gravimetric method, 
and the aggregate correction factor by the pressure method is so 
large and variable as to cast some doubt on the accuracy of air 
contents by that method. With the volumetric method, a known vol- 
ume of concrete is covered with water in a suitable container. The 
top level of the water is established by some suitable method. The 
air is then removed by stirring or rolling procedures and isopropyl 
alcohol is added to break up the bubbles and restore the liquid to 
its original level. The volume Ps liquid added is equal to the 
volume of air displaced. Menzel 5) has described a rolling method 
for the volumetric measurement of the air content of freshly-mixed 
concrete. The apparatus he used is shown in Fig. 4. 


Various other types of apparatus and procedures for meas- 
uring the air content of freshly-mixed concrete both by the, pres- 
sure method and the volumetric method have been descriped\>), 


A comparison of air contents determined by the rolling 
method with those determined by four other methods of test is 
shown in Fig. 5. Results opvtained by the various methods are in 
good agreement, except that with the slag aggregate the values 
obtained by the rolling method are considerably higher than those 
by the pressure method. 


DESIGN OF MIXES 


It is not within the scope of this paper to give a de- 
tailed discussion of the design of concrete mixes. Various 
methods are described in the literature. When air-entrained con- 
crete is used the mix must be designed to take account of the in- 
crease in air content. Air-entrained concrete contains a larger 
amount of air and requires less water than normal concrete. Each 
of these factors affect the yield and cement content of the mix. 

A change from normal concrete to air-entrained concrete requires 
@ redesign of the mix to retain the same yield and cement content. 


In general principle the mix should be redesigned by decreasing 

the volume of sand by an amount equal to the net change in the vol- 
ume of air plus water. Or, in other words, the volume of sand 
should be reduced by the amount required to retain the same yield 
and cement content. The Portland Cement Association publication 
"Design and Control of Concrete Mixtures" and the Highway Research 
Board Bulletin No eee "Use of Air-Entraining Concrete in Pave- 
ment and bridges"(6 give a detailed description of one method of 
mix design. 


LABORATORY METHODS OF TEST FOR SURFACE SCALING AND 
RESISTANCE TO FREEZING AND THAWING 


Since the primary purpose of laboratory studies was to 
develop methods of increasing the resistance of concrete to the dis- 
integration caused by the application of salts for ice removal or 
alternate cycles of freezing and thawing, it became necessary to 
design methods of test. Small concrete slabs 3 by 6 by 15-in. were 
used for the surface scaling test. These slabs were cast and fin- 
ished to simulate concrete pavement. A dike of 1 to 2 cement mortar 
was cast along the outer edges of the top surface of the slaps. 
Photographs of these slaps are shown in Fig. 6 and 15. The test in- 
volved freezing about a 1/4-in. layer of water on the top surface 
at 20° below zero and then thawing the ice thus formed by the appli- 
cation of raw flake calcium chloride in an amount equivalent to 
about 2.4 lb. per sq. yd. of surface. This cycle was repeated once 
each day until the surface of the specimen was badly scaled, or un- 
til it had been given 100 to 300 or more cycles without developing 
serious scaling. The surfaces were examined after each 20 cycles 
and rated as follows: 


No scaling - 0 
Very slight scaling - 1 
Slight to moderate scaling - 2 
Moderate scaling - 3 
Moderate to bad scaling - 4 
Bad scaling - 5 


Concrete prisms (generally 3 by 3 by 11g¢-in.) were used 
to study the resistance of concretes to repeated cycles of freez-— 
ing and thawing while immersed in tap water or in a 10 per cent 
calcium chloride solution. The following criteria were used to 
evaluate the resistance of these prisms to the freezing and thaw- 
ing treatment: 


(1) Linear expansion, 

(2) Change in modulus of elasticity (Sonic Method), 
(3) Loss in weight, 

(4) Loss in strength after a given number of cycles. 


RESISTANCE OF AIR-ENTRAINED CONCRETE TO SURFACE SCALING 

Fig. 6 shows photographs of the typical slabs containing 
non-air-entraining and air-entraining portland cements after they 
had been subjected to as many as 375 cycles of the surface scaling 
test. These photographs speak for themstlves. The specimens con- 
taining the air-entraining cements showed only slight or no scal- 
ing after as many as 300 to 375 cycles of this very severe test, 


* 6 * 


while companion specimens without the air-entraining addition showed 
serious scaling after 40 to 75 cycles. These results are typical of 
many others obtained during the past 15 years, and are in agreement 
with the performance of paving projects constructed with and with- 
out air-entrained concrete. 


The early experimental roads built with air-entraining 
portland cement provide ample evidence of the resistance of air- 
entrained concrete to the surface scaling resulting from the applica- 
tion of salts for ice removal. Fourteen experimental projects com- 
prising 7,439 slabs are situated in five northeastern states - Maine, 
Massachusetts, New York, Pennsylvania and Vermont. The first proj- 
ect was constructed in 1938 and additional and larger projects were 
constructed in 1939 to 1942. The sites used for these projects were 
chosen because of the heavy traffic, habitually severe winter weather, 
and frequent applications of rock salt or calcium chloride for ice 
removal. To determine the durability of different types of concrete 
pavement, the concrete used in the test slabs was made of one or an- 
other of the following cement variables: 


(1) Air-entraining portland cement, 

(2) Air-entraining portland cement blended with 
natural cement containing fat, 

(3) Normal portland cement blended with natural 
cement containing fat, 

(4) Normal portland cement blended with natural 
cement without fat, 

(5) Normal portland cement. 


The normal portland cements and their air-entraining coun- 
terparts were made at a number of different plants. The cements 
ased on one particular project were made at eight different plants. 
The air-entraining agents used in making the air-entraining portland 
cements included natural wood resin, beef tallow and codfish oil. 


The performance record of the 14 projects with respect to 
surface scaling is summarized in Table 1. These results clearly in- 
dicate the superior performance of the air-entraining portland cement 
concretes. None of the 2,095 slabs, in which air-entraining portland 
cement was the sole or principal cementing material, have developed 
the slightest indication of surface scaling. Of the 5,344 slabs not 
containing air-entraining portland cement, 2,445 or 46 per cent show 
scaling in some degree and on some of these the scaling has been so 
severe that they have been resurfaced. Many thousand miles of pave- 
ment built with air-entrained concrete since 1940 have shown equally 
good performance. 


Table 1 - Summary of Air-Entraining Test Road Condition 


Survey Results in 1952 
Average age pbepiiiy Ac) age: 


nnn ene ULEnEEDEIDEEInnInnInnunnnnnnTnE 


a 
No. of No. of Percentage 


Type of Cement Slabs Slabs of 
Laid ocaled Total 


a 


Air-Entraining Portland Cement .-.eee.. 1,673 0 8) 
Air-Entraining Portland Cement Blended 

with Natural Cement Containing Fat.. 422 @) 0 
Normal Portland Cement Blended with 

Natural Cement Containing Fat eevee 3,833 1,459 38 
Normal Portland Cement Blended with 

Natural Cement without Fat eeecccsee 178 178 | 100 
Normal Portland Cement cevescccccsvesesee 1,333 808 61 


ert A ne 


RESISTANCE OF AIR-ENTRAINED CONCRETE TO FREEZING AND THAWING 


The diagrams in Fig. 7 show the effect of entrained air on 
the resistance of concretes to alternate cycles of freezing and 
thawing. The cements used for these tests were ground without and 
with tallow or natural wood resine These diagrams are similar to 
many others that have been obtained with different air-entraining 
cements and different air-entraining admixtures. A minimum air con- 
tent of 3 per cent usually provides excellent resistance to freezing 
and thawing for concretes having maxium size aggregates of 13 tome au. 
The concretes with 3 per cent entrained air showed about as good 
resistance as those with higher air contents. This is indicated by 
the low expansion, small reduction in modulus of elasticity and low 
loss in weight after 225 cycles of freezing and thawing for the 
concretes containing 3 per cent or more entrained air. With air 
contents only slightly below 3 per cent, the resistance to freezing 
and thawing decreases rapidly. 


One series of laboratory tests was made to determine the 
effect of cement composition, cement fineness, cement content and 
water-cement ratio on the frost resistance of concretes. Five 
portland cement clinkers were selected to represent the approximate 
range in chemical composition encountered in portland cement. They 
represented clinker normally used in making cements of Types I, II, 
III and IV. Each clinker was ground to obtain cements having surface 
areas of 1400, 1800 and 2200 sq. cm. per g. respectively. These 
cements were used in the preparation of concretes having cement con- 
tents of 4, 54, and 7 sk. per cu.yd., water-cement ratios ranging 
from 4.5 to 9.8 gal. per sk. of cement. Three of the cements were 
used also in the preparation of air-entrained concretes by adding 
an air-entraining agent at the mixer to obtain increasing incre- 


ments of entrained air in the concretes. These air-entrained con- 
cretes had a cement content of 7 sk. per cue yd. The concretes 


* 8 


were cured 28 days in the moist room and 3 days in water and then 
subjected to alternate cycles of freezing and thawing. 


Fig. 9 shows the results of the freezing and thawing 
tests of the concretes. This figure shows the air content of the 
concretes and the number of cycles of freezing and thawing re- 
quired to produce a 50 per cent reduction in modulus of elasticity, 
dynamic E, which is equivalent to approximately 70 per cent re- 
duction in flexural strength. All of the non-air-entrained con- 
cretes used in these tests had relatively low frost resistance and 
appear in the small square in the lower left-hand corner of the 
figure. Regardless of the wide range in cement composition, ce- 
ment fineness, cement content and water-cement ratio, only apout 
100 cycles were required to produce a 50 per cent reduction in the 
modulus of elasticity of the most-resistant non-air-entrained con- 
eretes. However, with purposely entrained air the frost resistance 
increased abruptly. With air contents in the range of 3 to 6 per 
cent it required 1000 cycles, or more, of freezing and thawing to 
produce a 50 per cent reduction in modulus of elasticity. Although 
there were some variations in the frost resistance of the non-air- 
entrained concretes made with cements of different composition or 
fineness, or with different cement contents and water-cement ratios, 
these variations were insignificant in comparison with the very 
large increase in frost resistance that can be obtained with pur- 
posely entrained air. 


Coneretes exposed to natural weathering provide further 
evidence of the resistance of air-entrained concrete to freezing 
and thawing. In the Long-Time Study of Cement Performance in 
Concrete, near-job-size structures have been constructed on a test 
plot at Naperville, Illinois where conditions of freezing and 
thawing are severe in the winter. Included in these structures 
are cast-in-place box-type specimens 24 ft. on a side filled with 
soil and water to represent concrete retaining walls. Fig. 11 
shows the condition of two of the poxes after 11 winters. These 
two boxes were made using a lean mix (4% sk. of cement per cu. yd.), 
a high slump (8-in.), a sand that has a poor service record, and 
@ gravel that has a good service record. The sand had a high shale 
content. The badly deteriorated box at the left was made with a 
Type I cement. The box at the right, which is in excellent condi- 
tion, was made with a Type I air-entraining cement. both cements 
were made at the same plant and from the same batch of clinker. 
These two voxes are representative of many similar comparisons that 
can be seen at the Naperville, Illinois test plot. They provide 
convincing evidence of the superior frost resistance of air- 
entrained concrete. 


RESISTANCE OF AIR-ENTRAINED CONCRETE TO D-CRACKING 

D-cracks are defined as fine, parallel cracks, usually 
filled with a dark-colored deposit, probably calcium carbonate, 
which forms along the edges of the joints and structural cracks 
and sometimes along the free edges of pavement slabs. They are 
usually considered to be evidence of weathering leading some- 
times but not always to ultimate disintegration. Fig. 11 shows 
the first stage of D-cracking at the intersection of the longi- 
tudinal joint and an expansion joint of a pavement built without 


e OU 


‘air entrainment. Fig. 12 shows more advanced stages of deteriora- 
tion. The D-cracks have extended into the body of the slab. 


Air-entrained concrete resists the development of D-crack- 
ing as shown (7 Table 2. This table is taken from a paper by 
F. H. Jackson and represents results obtained on the New York 
Test Road of the Long-Time Study of Cement Performance in Concrete. 


Table 2 -Projects 1 and 1A.New York Test Road, Condition of Pavement 


Slabs with Respect to Evidence of Accelerated Weathering (D-Cracks 
Ratings as of June lL : Road constructed 1942 


TYPE I CEMENTS 


su SOA doa sal at Ab ome 18 TOTAL 
No. of (75 ef£08 oO ladies ccs vies eo 16 8 8 See aS 8 8 80 


Slabs Showing D—Cracks..... JQ il ail ) Z i. g 
TYPE IIT CEMENTS 
Pad 22 2 2 4 TOTAL 
Nov of 75-f£t."Slabses cee ce 16 8 8 8 8 48 
Slabs Showing D-Crackseese. 10 ib 1 tL 1 14 
ATR-ENTRAINING CHMENTS 
pat 16T 217° = SPCraAu 
Noe of -75-f£0 Sto lave eerccca es 16 16 16 48 
Slabs Showing D—Cracks...e.- 0 0) 0 0 


These data reveal several interesting points. In the 
first place it will be noted that none of the 48 slabs constructed 
with air-entraining cements (12T, 16T, 21T) shows any evidence of 
D-cracking after 7 years! exposure. On the other hand, 8 out of 
80 slabs constructed with non-air-entraining Type I cements, or 
10 per cent, show D-cracking, and 14 out of 48 slabs constructed 
with Type II non-air-entraining cements, or 29 per cent, show evi- 
dence of such cracking. It is interesting to note also that the two 
non-air-entraining cements (16, 21) which show the greatest amount 
of D-cracking are entirely free from D-cracking in the slabs made 
of their air-entraining counterparts (16T and 21T). (Note: The 
Long-Time Study of Cement Performance in Concrete was undertaken 
prior to the adoption of the ASTM Tentative Specification for Air- 
Entraining Portland Cement. For that reason the air-entraining 
cements used in that study were called "treated cements" and are in- 
dicated by the letter "I" following the cement number.) 


Many additional pavements constructed with air-entrained 
concrete provide further evidence that air-entrained concrete re- 
sists the development of D-cracks. 


STRENGTH OF AIR-ENTRAINED CONCRETE 


The strength of air-entrained concrete (at a constant air 
content) is principally dependent on the water-cement ratio. Thus 
an air-entrained concrete mixture can be designed to provide any de- 
Sired strength in a manner similar to non-air-entrained mixtures. 
For concretes having the same cement content, air-entrainment tends 
to reduce the strength for rich mixtures. With lean mixtures or 
with small maximum size aggregates, air-entrainment is accompanied 
by relatively larger reductions in water requirement and for these 
mixtures the strengths will not be reduced, they may even be in- 
creased, by the use of air-entrainment. It is generally agreed that 


Jee Chae 


the air content required to provide satisfactory durability will 

not result in serious loss in strength of concretes of constant 
cement content, particularly if advantage is taken of the greater 
workability of the air-entrained concrete to reduce the sand and 
water content of the mixture. However, even under these conditions, 
any marked increase in air above the recommended amount will further 
reduce the strength without commensurate improvement in durability. 
With concretes having a cement content of 6 sk. per cue. yd., or more, 
and maximum size of aggregates of 1-1/2 to 2-in., each percentage 
increase in the amount of air above the amount which exists in the 
normal concrete reduces the flexural strength 2 to 3 per cent and 
the compressive strength 3 to 4 per cent, as shown in Fig. 8. Con- 
sequently, when using air-entraining materials, it is necessary to 
make sure, not only that the mix is properly designed, but also that 
the air content is maintained within reasonable limits of tolerance 
throughout the work. 


BOND BETWEEN CONCRETE AND STEEL 


Data showing the effect of air entrainment on the bond re- 
sistance of reinforcing bars embedded in air-entreined concrete are 
limited. Such data 2s are availabl2 indicate that bond resistance 
is influenced in about the same manner as compressive strength when 
the air content of the concrete is increased. In a series of tests 
on beams (4-7/8 by 12 by 64-in.) reinforced with a single l-in. 
round commercial deformed bar with transverse lugs, the air content 
of the fresh concrete was varied from 1 to 6.4 per cent by varying 
the amount of air-entraining agent added at the mixer. The cement 
content of the concrete was 5 sk. per cu. yd., the slump was 5 to 6 
inches, and the concrete was placed by hand rodding. Both the con- 
pressive strength of the concrete and the bond resistance developed 
by the beams decreased approximately 3% for each percentage point 
increase in air content over the range of 1 to 6.4 per cent. In 
these tests the beams did not show any significant differences in 
the development of cracks with increasing amounts of entrained air. 
Inasmuch as the ratio of bond strength to compressive strength of 
air-entrained concrete is essentially the same as that of normal 
concrete, it is only necessary to specify the minimum compressive 
strength desired. 


The use of the better types of commercial deformed bars, 
meeting ASTM Specification A305, and the employment of concrete 
of the lowest slump possible for the conditions of placing to be 
encountered, should provide adequate bond resistance where the air 
content of the concrete is held within reasonable limits. Where 
possible the concrete should be placed by vibration and full ad- 
vantage should be taken of the reduction in mixing water that can 
be effected by air entrainment and by reducing the sand content of 
the mix to the lowest amount consistent with good placeability. 


SULFATE RESISTANCE OF ATR-ENTRAINSD CONCRETE 

The disintegration of concrete from contact with al- 
kalin sulfates is a problem of lons standing in many localities. 
It has been demonstrated that concrete can be made that will 
resist the attack of aggressive sulfate waters. Cements of low 


% ll * 


C3A content, Type II or Type V cement, should ve used in con- 
cretes that are to be exposed to sulfate waters. The concrete 
should have a low water-—cement ratio. Entrained air also in- 
proves the sulfate resistance of portland cement concrete as 
shown in Fig. 13. The beams at the left show that without air 
entrainment the concretes made with cement contents of 4 and 5% 
sk. per cu. yd., are badly deteriorated after 5 years' exposure 
to an alkali soil while the concrete made with a 7-sack mix is 
in good condition. By comparison the beams at the right which 
are in much better condition, particularly in the lean mixes, 
show the beneficial effect of air entrainment. 


Papers by L. A. Dahi(8) , Thomas E. Stanton\9), end, 9) 
F. R. McMillan, T. E. Stanton, I. L. Tyler and W. C. Hansen , 
provide more detailed information on the sulfate resistance of 
portland cement concretes and the beneficial effect of air en- 
trainment. 


ABRASION RESISTANCE OF AIR-ENTRAINED CONCRETE 


Witte and Backstrom(11) made extensive laboratory tests 
of the abrasion resistance of air-entrained concrete using the 
shotolast method. Sixty-six concrete mixes covering a range of 
eleven water-cement ratios ranging from 0.40 to 0.70 by weight, 
and six air contents varying from 0.2 to 16.8 per cent were used 
for the tests. The authors concluded that compressive strength 
was the most important factor controlling the abrasion resistance 
of concrete; abrasion resistance increased as the compressive 
strength increased. Air entrainment influences the resistance 
to abrasion but only in so far as it affects the compressive 
strength of the concrete. 


PERMEABILITY OF AIR-ENTRAINED CONCRETE 


Air entrainment reduces the passage of water through 
the concrete. Air-entrained concrete, after it has once dried, 
is more resistant to the passage of moisture than regular con- 
crete, and it will absorb less water. Small disconnected air 
voids offer a barrier to the passage of water. Silos for the 
storage of portland cement showed no caking of the cement on the 
inside when built with air-entrained concrete, whereas those 
built with regular concrete exhibited the usual amount of caking 
along the periphery of the silo. Aside from the increased water- 
tightness inherent in air-entrained concrete, the greater degree 
of uniformity, due to increased eh ana a of the concrete as 
placed, improves impermeability(l2 ° 


AIR-ENTRAINED CONCRETE IN THE PRODUCTION OF CONCRETE PIPE AND pLOCK 


A numoer of concrete pipe manufacturers use small amounts 
of entrained air in plastic mixes in the manufacture of concrete 
pipe py the casting process. Concrete pipe generally are not 
subjected to repeated cycles of freezing and thawing. Therefore, 
air entrainment is used primarily as a means of increasing worka- 
bility and cohesiveness of the concrete and reducing segregation 
and bleeding. This results in a more uniform concrete through- 
out the pipe. Entrained air in amounts of 2 to 3 per cent would 
be ample to provide for these requirements. 


*#12% 


Manufacturers report that air entrainment in concrete 
pipe made by the centrifugal process has resulted in objection- 
able foaming during spinning. Because of this, entrained air 
has not been used with this process. 


In concrete products, such as concrete pipe or block 
made oy the compaction of a dry non-plastic mix, air entrain- 
ment has been found by some manufacturers to improve the degree 
of compaction, the uniformity of surface texture and the ability 
of the freshly molded product to withstand handling with less 
breakage or other damage. However, in some cases no advantage 
was reported. Hence it appears that the matter of air entrain- 
ment should be determined by trial by each manufacturer under his 
normal plant operations. 


BLENDS OF PORTLAND CEMENT WITH NATURAL CEMENT 


Many natural cements contain air-entraining agents, 
others do not. When blended with portland cement, the natural 
cements that contain air-entraining agents will incorporate air 
in the concrete and thereby improve the resistance to freezing 
and thawing and to the surface scaling resulting from the use of 
salts for ice removal. Naturel cements that do not contain air- 
entraining agents produce no such improvement in the concrete. 


Kellerman and Runner(13) studied the resistance to 
freezing and thawing of concrete made with blends of non-air- 
entraining portland cement and two different natural cements. 
They used 14 and 28 per cent py weight, of natural cement re- 
placing the portland cement. One of the natural cements con- 
tained an air-entraining agent and when substituted for the 
portland cement it increased the resistance of the concrete to 
freezing and thawing. The other natural cement did not contain 
an air-entraining agent. Blends of this natural cement with 
the portland cement produced concretes having lower resistance 
to freezing and thawing than concretes made with the portland 
cement alone. 


A. A. Anderson(24) also has reported results of tests 
of blends of natural cements with portland cements. In one 
series of tests, two natural cements were used, each of which 
was used both with and without the addition of an air-entrain- 
ing agent. Each of the natural cements was blended with a non- 
air-entraining portland cement (5 parts portland cement plus l 
part natural cement by weight). Fig. 14 shows the relative 
resistance to freezing and thawing of specimens made with these 
cements as measured by the reduction in the modulus of elas- 
ticity (sonic method) and by linear expansion. Curves 4 and C, 
representing the blends of the two natural cements without the 
air-entraining agent, indicate that these blends have practical- 
ly no advantage over the concrete made with the non-air- 
entraining portland cement as represented by Curve A. Curves D 
and E, however, representing concretes made from blends of the 
Same natural cements, except that in this case the natural ce- 
ments had been ground with an air-entraining agent, show greatly 
improved resistance for the blends. The air content for each 
concrete is indicated on the figure, and here again it will be 
seen that the durapility improves with the increase in air con- 
tent. 


1 3 3 


In another series of tests, the slabs used for the 
laboratory surface scaling test were cast from the concrete used 
in a pavement project. The cements used on this job included: 

A non-air-entraining portland cement, an air-entraining portland 
cement, and a blend of the non-air-entraining portland cement 
with natural cement. Fig. 15 illustrates the surface condition 
of the slabs after 50 or 300 cycles of freezing followed by the 
application of calcium chloride to remove the ice frozen on the 
surface of the slabs. The superior resistance to surface scaling 
of the concrete made with the air-entraining portland cement is 
apparent. 


Data in Table 1, discussed previously, show the re- 
sults obtained using blends of portiand cement with natural ce- 
ment on resistance to surface scaling of the experimental roads 
in the northeastern states. 


COLORING AGENTS — THEIR EFFECT ON AIR CONTENT AND DURABILITY 


Field reports on the performance of colored concrete 
pavements have indicated that certain coloring agents decreased 
the durability of the concrete. This led to an extensive lab- 
oratory study (15) of the "Effect of Carbon Black and Black Iron 
Oxide on the Air Content and Durability of Concrete." It was 
found that some of the coloring agents reduced the air content 
of the fresh concrete as shown in Fig. 16. This reduction in air 
content was accompanied by a decrease in resistance to surface 
scaling and to alternate cycles of freezing and thawing in tap 
water. When these same colorins agents were used with additional 
amounts of an air-entraining agent to obtain concretes having from 
3 to 6 per cent entrained air, the concretes had excellent resistance 
to surface scaling and to alternate cycles of freezing and thawing. 
Some producers of coloring agents have taken advantage of this in- 
formation and are now furnishing materials that do not reduce the 
air content of the concrete. 


EFFECT OF MIX PROPORTIONS AND AGGREGATE GRADATION ON 
THE AIR CONTENT OF CONCRETE 


Klieger(16s17) nas reported the effect of entrained air 
on the strength and durability of concretes made with various 
maximum size aggregates. He found that the mix proportions and 
aggregate gradation have a pronounced effect on ths air content 
of the concrete, both for non-air-entraining and air-entraining 
cements, as shown in Fig. 18. The tests were made on concretes 
having a nominal slump of 2 to 3 inches and with cement contents 
of 4, 5% and 7 sk. per cu. yd. Additional tests have shown that 
Similar relationships to those shown in Fig. 17 exist for con- 
cretes of higher slump. There was no significant change in the air 
content of the concretes when the maximum size of the aggregate 
was decreased from 24 in. to 14 in.; there was a slight increase 
in the air content when the aggregate was decreased fron 13 in. 
to 3/4-in., and a sharp increse in the air content of the con- 
cretes as the maximum size of the aggregate decreased from 3/4 in. 
to No. 4. 


* 14 * 


Fig. 18 shows th: effect of entrained air on the water 
requirements of the concretes made with varying maximum size 
aggregates. The reduction in the water required, with increas- 
ing increments of entrained air, was more pronounced in the lean 
mixes than in richer mixes; and for any one cement content the 
reduction was greater with the small aggregates than with the 
larger maximum size aggregates. 


Fig. 19, 20 and 21 show the effect of entrained air on 
the modulus of rupture and compressive strength of concretes made 
with varying maximum size aggregates. For a given cement content, 
the effect of entrained air on both flexural and compressive 
strength was compensated to a considerable degree by the decrease 
in water required with increased air content. All of the lean 
mixes, and the rich mixes made with the smaller size aggregate, 
show very little, if any, reduction in strength with increasing 
air content. In the richer mixes made with the larger size 
aggregates, where increasing air contents were accompanied py a 
relatively smaller reduction in the water requirement, the 
modulus of rupture and compressive strength decreased progressive- 
ly with increasing air contents. 


Fig. 22 shows the effect of entrained air on the re- 
Sistance to freezing and thawing of concretes made with differ- 
ent maximum size aggregates. This figure shows the per cent 
expansion during 300 cycles of freezing and thawing. The tests 
were made with concretes having cement contents of 4, 54 and 
7 sk. per cue yd. The results of these tests indicate that con- 
cretes made with small aggregates require higher air contents 
for frost resistance comparable to that of concretes containing 
larger aggregates. The entrained air is contained in the mortar. 
The amount of mortar required to produce a workable concrete de- 
pends on the cement content and the maximum size of the aggre- 
gate. On the basis of these tests, the air contents required 
for frost-resistant concretes made with different maximum size 
aggregates are shown in Table 3. It has been shown in labora- 
tory tests, Fig. 17, that, in general, the use of air-entrain- 
ing portland cement affords a self-regulating means for pro- 
viding the approximate air content required for the different 
maximum size aggregates. 


Table 3 — Air Contents Required for Frost-Resistant Concretes 
Made with Different Maximum Size Aggregates 


Maximum Size of Coarse Aggregate, Air Content, 
an’ @ by Volume 
14% to 23% 4e + 18 
ie at ae 1h 
3/8 7 +13 
faye 9 + 1h 


* 15 * 


EFFECT OF SLUMP AND VIBRATION ON THE AIR CONTENT OF CONCRETE 


The air content of fresh concrete varies with the 
slump and vibration decreases the air content. Fig. 23 shows 
the effect of slump and vibration on the air content of the 
fresh concrete. Air-entraining cements containing two differ- 
ent air-entraining agents were used in these tests. The two 
diagrams at the top are for concretes mixed in a Lancirick 
(tub type) mixer, the lower diagrams are for concretes mixed in 
a tilting drum type mixer. The concretes were vibrated 3 minutes 
in these tests. 


The different diagrams indicate that the results are 
Similar for the cements containing the two different air-entrain- 
ing agents and for the two types of mixers. The air content increas- 
ed as the slump increases up to 6 to 7 in. Further increases in 
slump were accompanied by a rapid decrease in the air content. 
The 3-minute vibration caused a considerable reduction in the air 
content. Internal vibration reduced the air content more than ex- 
ternal vibration. 


A normal amount of vibration reduces the initial air 
content about 10 per cent while with prolonged vibration there 
is a progressive further reduction in the air content of the 
concrete. Fig. 24 shows the effect of duration of vibration on 
the air content of concretes having a slump of 3 to 4 inches. 
With vibration for 1/2 minute the air content was reduced from 
10 to 15 per cent, while with l-minute vibration the reduction 
in air content was about 15 to 20 per cent. 


EFFECT OF TEMPERATURE ON THE AIR CONTENT OF CONCRETE 


Fig. 25 shows the effect of the temperature of the con- 
crete on air content for concretes having slumps ranging from 1.0 
to 7.0 inches. The concretes used in these tests had a nominal 
cement content of 6 sk. per cu. yd. The mixing time was 3 minutes. 
The diagram at the left is for an air-entraining cement contain- 
ing agent "A" while that at the right is for a cement containing 
agent "bp", 


For both cements, the air content tends to decrease 
as the temperature of the concrete increases. This effect becomes 
more pronounced as the slump of the concrete increases. 


The temperature caused less variation in the air con- 
tents of the concretes made with the cement containing neutral- 
ized agent "A" than for those made with the cement containing 
agent "B", 


With the cement containing agent "A", there was a pro- 
gressive decrease in air content as the temperature of the con- 
crete was increased from 42° to 98°F. With agent "B" the air 
content reached a minimum at about 85° F. and then increased 
slightly with higher temperatures. 


* 16 * 


EFFECT OF MIXING TIME ON AIR CONTENT OF CONCRETE 


The effect of mixing time on the air content of con- 
crete deserves particuler attention, especially in connection with 
ready-mixed concrete operations. Ready-mixed concrete, by its 
very nature, is mixed and agitated for a longer time than job-mixed 
concrete. Periods of 15 minutes or more of combined mixing and 
agitation are the rule as compared with the conventional one or two 
minutes in the job mixer. 


Fig. 26 shows the effect of mixing time on the air 
content of the fresh concrete. A non-air-entraining cement, two 
air-entraining cements,and a blend of the two air-entraining cements 
were used for these tests. 


The mixing time had no significant effect on the air 
content of the concrete made with the non-air-entraining cement. 
With the air-entraining cements the air content was increased about 
1.9 per cent when the mixing time was increased from 1 minute to 
5 minutes. It then remained practically the same with 5 minutes 
additional mixing. When the mixing time was extended beyond 10 
minutes, there was a gradual decrease in the air content and after 
40 to 60 minutes total mixing it was about the same as that obtained 
with one-minute mixing. 


The effect of mixing time was very nearly the same for 
the two air-entraining cements. The blend of equal parts of the two 
air-entraining cements gave air contents that were intermediate of 
those for the individual cements. 


EFFECT OF PERCENTAGE OF SAND ON THe AIR CONTENT OF CONCRETE 


The air content of the concrete varies with different 
sand contents, as shown in Fig. 27. Reducing the sand per- 
centage caused the air content of the concrete to decrease. These 
tests were made with a non-air-entraining cement and with the same 
cement with an air-entraining agent added at the mixer. The tests 
are for concrete mixes containing 5 and 6 sk. of cement per cu. yd. 
The diagrams at the left are for concrete having slumps of 3 to 4 
inches, those at the right for slumps of 6 to 7 inches. 


The reduction in the percentage of sand was accompanied 
by a reduction in the water content of the concrete. For the 
mixes containing entrained air, there was a tendency for the 
strength to increase slightly with each decrease in the percentage 
of sand in the mix. The effect of sand reduction on both air con- 
tent and strength was similar in character for both consistencies 
and for both cement contents. 


CONCLUDING REMARKS 


The results obtained with air-entrained concretes, 
either when produced by the use of air-entraining cements or air- 
entraining agents added at the mixer, have consistently shown 


* 17 * 


their marked improvement in resistance to surface scaling and to 
alternate cycles of freezing and thawing. The performance to 
date of the many paving projects built with air-entrained con- 
crete parallels the results obtained in the laboratory tests. 
Air-entrained concrete is now being used extensively in pave- 
ments and its use in other types of construction such as bridges, 
buildings, dams and in concrete products is increasing rapidly. 
The beneficial properties of air-entrained concrete such as in- 
creased workability, greater cohesiveness, reduction in segrega- 
tion and reduction in bleeding all tend to produce a more homo- 
genous mass, better appearing structures and more durable con- 
crete. Eventually it may be used in practically every type of 
concrete construction. 


All the care and precautions used with normal con- 
crete should be used also with air-entrained concrete. Sound, 
durable and properly-graded aggr-gates should be used. The mix 
Should be properly designed. Full advantags should be taken of 
the reduction in water-cement ratio that can be obtained with 
air-entrained concrete. The air content of the concrete must 
be maintained within proper limits. It cannot be left to chance. 
It shouldbe checked repeatedly during the construction opera- 
tions. Apparatus is now available for the rapid and accurate 
determination of the air content. A number of variables that 
affect the air content of the concrete have peen described in 
this paper. When the air content is either above or below the 
desired limit, adjustments made for one or more of these vari- 
ables should provide the required air content. 


The results described in this report were taken in 
large part from laboratory and field studies made py the 
Research Laboratories of the Portland Cement Association. The 


conclusions cited in the text have been substantiated and con- 
firmed by similar studies made py other laboratories and agencies. 


* 18 * 


(End of Text) 


1953 


REFERENCES 


(1) Air Entrainment in Concrete: Jl. Am. Concrete Inst., 


(2) 


(3) 


(4) 


Doom loa esr POC sev. 40s Dey 1p eLOans 


(a) "Tests of Concretes Containing Air-Entraining 
Portland Cements or Air-Entraining Materials 
Added to Batch at Mixer," py H. F. Gonnerman. 
Reprinted as Bulletin 13 of the Research 
Laboratories of the Portland Cement Association. 


(b) "Concretes Containing Air-Entraining Agents" - A 


Symposium - Contributions py: Myron A. Swayze 
Guy H. Larson 

Frank H. Jackson Robert A. Burmeister 

Henry L. Kennedy Stanton Walker 

Harmon S. Meissner Raymond E. Davis 

Donald R. MacPherson Joseph H. Chubb 

George L. Lindsay R. T. Sherrod 

Harry F. Thomson J. F,. Barbee 


F. V. Reagel 


(c) "Laboratory Studies of Concrete Containing Air- 
Entraining Admixtures," by Charles £, Wuerpel 
Proc. Am. Concrete Inst., v. 42, p- 305, 1946 


"The Camera Lucida Method for Measuring Air Voids in 
Hardened Concrete," by George J. Verbeck; Jl. Am. Concrete 
Inst., May 1947; Proc., ve 43, pe 1025, 1947. Reprinted 
as Bulletin 15 of the Research Laboratories of the 
Portland Cement Association. 


"Linear Traverse Technique for Measurement of Air in 
Hardened Concrete," by L. 5. brown and C. U. Pierson; 

Je Ame Concrete Inst., October 19503; Proce’, v.47, p. LL7. 
Reprinted as Bulletin 35 of the Research Laboratories of 
the Portland Cement Association. 


"A Method for Direct Measurement of Entrained Air in 
Concrete," by W. H. Klein and Stanton Walker; Jl. Am. 
Concrete Inst., June 1946; Proc., v. 42, ps 657, 1946. 


"Development and Study of Apparatus and Methods for the 
Determination of the Air Content of Fresh Concrete," py 
Carl A. Menzel; Jl. Am. Concrete Inst., May 1947; Proc., 
ve 43, pe 1053, 1947. Reprinted as bulletin 16 of the 
Research Laboratories of the Portland Cement Association. 


#19 %* 


(5) "Procedures for Determining the Air Content of Freshly- 
Mixed Concrete by the Rolling and Pressure Methods," 
by Carl A. Menzel. Reprinted from Symposium on 
Measurement of Entrained Air in Concrete, published 
in Proc. Am. Soc. for Testing Mat., v. 47, 1947~ 
Reprinted as Bulletin 19 of the Research Laboratories 
of the Portland Cement Association. Other contribu- 
tions in Symposium were: 


A. TL. Goldbeck 

John H. Swanberg and T. W. Thomas 

Alexander Klein, David Pirtz and C. B. Schweizer 
H. W. Russell 

W. A. Gordon and H. W. Brewer 

J.C. Pearson 

J. F. Barbee 

J. CG. Pearson and S. 56. Helms 


"Washington Method of Determining Air in Fresh Concrete," 
by Bailey Tremper and ¥. L. Gooding, p. 210, Proc. 
Highway Research Board, 1948. 


(6) "Use of Air-Entraining Concrete in Pavements and bridges," 
Bulletin 13R (Current Road Problems) of the Highway 
Research Board, May 1950. 


(7) "Why Type II Cement," by F. H. Jackson, Proc. Am. Soc. 
for Testing Mat., ve 50, p- 1210, 1950 . 


(8) "Cement Performance in Concrete Exposed to Sulfate Soils," 
by L. A. Dahl; Jl. Am. Concrete Inst., December 1949; 
Proce, Ve 46, pe 2575 1950. 


(9) "Durability of Concrete Exposed to Sea Water and Alkali 
Soils - California Experience," by Thomas E. Stanton; 
Jl. Am. Concrete Inst., May 1948; Proc., ve 4Aepeeee 
1948. 


(10) "Long-Time Study of Cement Performance in Concrete, 
Chapter 5, Concretes Exposed to Sulfate Waters," by 
F. Re McMillan, ot. sh. Stanton, ley Leeky ler eeu 
W. C. Hansen. Special publication, Am. Concrete Inst. 
Reprinted as Bulletin 24 of the Research Laboratories 
of the Portland Cement Association. 


(11) "Some Properties Affecting the Abrasion Resistance of Air- 
Entrained Concrete," py L. P. Witte and J. E. Backstrom, 
Proc. Am. Soc. for Testing Mat., v.51, p. LIA oa 


(12) "Practices, Experiences and Tests with Air-Entraining 
Agents in Making Durable Concrete," by Ropert F. Blanks 
and W. A. Cordon, Jl. Am. Concrete Inst., v. 45, 
p- 469, 1949. 


(13) "The Effect of Using a Blend of Portland and Natural 
Cement on Physical Properties of Mortar and Concrete," 
by W. F. Kellerman and D. &. Runner; Proc. Am. Soc. 
Testing Mat., v. 38, Part II, p. 329-350. 


* 20 * 


(14) 


(15) 


(16) 


(17) 


"Treated Cement Concrete Resists Scaling," by 
A. A. Anderson; The Explosives Engineers, 
January 1942, p. 10. (Published py Hercules Powder 
Company, Wilmington, Delaware). 


"Effect of Carbon Black and black Iron Oxide on the Air 
Content and Durability of Concrete," py Thomas G. 
Taylors; Jl. Am. Concrete Inst., April 19483 Proc., 
ve 44, No. 8, p. 613, 1948. Reprinted as bulletin 23 
of the Research Laboratories of the Portland Cement 
Association. 


"Effect of Entrained Air on Concretes Made with So-Called 
'Sand-Gravel! Aggregates," py Paul Klieger; Jl. Am. 
Concrete Inst., October 19483 Proce, ve 455 pe 149, 
1949. Reprinted as bulletin 24 of the Research 
Laboratories of the Portland Cement Association. 


"Studies of the Effect of Entrained Air on the Strength 
and Durability of Concretes Made with Various Maximum 
Sizes of Aggregates," by Paul Klieger, Proc. Highway 
Research Board, January 1952. 


* 21% 


Research Laboratories of the 
Portland Cement Association 


33 West Grand Ave. 
Chicago 


NORTH LANES CONSTRUCTED WITH SOUTH LANES CONSTRUCTED WITH PORTLAND 
NORMAL PORTLAND CEMENT GROUND WITH NATURAL WOOD RESIN 
Bad surface scaling No scaling 


(b) ILLINOIS EXPERIMENTAL PAVING PROJECT, FA, 133, SEC, 2021, ARCHER AVENUE, 
CHICAGO, AFTER TWO WINTERS' EXPOSURE TO SALT ACTION AND FREEZING AND THAWING 


FIG. 1 - PHOTOGRAPHS OF PORTIONS OF SURFACES OF TWO EXPERIMENTAL PAVING PROJECTS 


FIG.1A - ILLINOIS EXPERIMENTAL PAVING PROJECT, ARCHER AVENUE 
CHICAGO, AFTER SEVEN WINTERS’ EXPOSURE TO SALT ACTION 


VILA AMM » fet 8 SS 
“AND FREEZING AND THAWING 


This lane was constructed with portland cement 
ground with natural wood resin 
No scaling 


Research Laboratories of the 
Portland Cement Association 
33 West Grand Ave. 
Chicago 


S 


° ° 
Ch oS 
Lee 
Oe ise 
Co? 
A ° 
° 


Outlined ‘areas t 
are air voids 


2 ew 


Concrete 
Osks. per cu.ud. 


Shaded areas 
are aggregate 


Fig.2- Observed Air Voids in Hardened Concretes 


Cae aal 


Research Laboratories of the 
Portland Cement Association 
33 West Grand Ave. 
Chicago 


FIG. 3 - PRESSURE TYPE ENTRAINED AIR INDICATOR OF 0,22 CU, FT, CAPACITY AND ACCESSORIES 


View at left shows close-up of assembled indicator, The view at right shows 
the same indicator for test, supported on the chest in which it is packed during 
shipment. The chest also houses the various accessories shown in center view, 


The accessories are as follows: (1) Trowel for selection of sample and fil- 
ling bowl,(2) Rodding tool, (3) Rawhide mallet, (4) Strike-off bar, (5) Funnel, 
(6) Two-quart measure, (7) Socket wrench for set screws in clamps, (8) Brass 
container of known volume for calibrating and checking indicator, (9) Spring to 
hold container 8 in position during calibration test, (10) Bar for adjusting 
thrust nut at lower end of precision bore glass tube, (11) Brass tube with per- 
forated end for filling indicator with water, (12) Brush for cleaning glass tube 


Ser. dls sel saya, 


FIG. 4 - SQUIPMENT FOR DETERMINING ENTRAINSD AIR CONTH#NT OF FRESHLY-MIXED 


CONCRETE BY THE ROLLING METHOD 


When filled, the 8 by &-in, bowl in uvper view accommodates a 0,22 cu. ft, sample of concrete, 


Lower view shows use of cradle to tilt assembly and permit rolling in inclined positions, 
Ser, 341, 1/31/u7 


8 
7 {bee Test! Elgin sand with Lab. Tests: Elgin sand withe 
gin grave ° ? Elgin gravel o7 -Air- ini ir- ini 
; Dresser traprock —* € ote Ok eae We od Air eniraining” ia Ee at la, 
a: y porous slag Le : ae : , hie 
2 7 ~~ WOO 
o 758 a xo Resin 
4 40 A 
wale 
O a 
Sue 
s I + ,--~Tallow 
ey 0 
@) x 
> 8 . . 
Lab Tests: Elgin sand with /“ Lab. Tests: Elgin sand with 936 
re 7 F£lgin gravel ------- Elgin gravel -------- Ge gee 
g | Dresser traprock—-« Highly porous slag--x x 
tS re) 08” Ma 
peed P = i, carton? 
<< Ste = 
= 4 2 2 NEW YOR 
Cc 
5 |s = 3 
O 312 6 = 
Ie er b3 
Lee? wie = 
4°) 
! Vai Sati MINNEAPOLIS ,SECOND AVE. RESURFACING 
olling 
0 
Ocoee te SerG P78 Os levee .3 ©45°5% 6 7 8 


Percent Air by Rolling Method 


a FIG. € - SURFACES OF TYPICAL 3x6x15-IN, CONCRETE SLABS FROM FOUR 
. - oD WITH = + GENER soa ee eet 
Ei6.) 9 MPARISON OF AIR CONTENTS BY THE ROLLING METH EXPERIMENTAL ROAD PROJECTS AFTER TEST FOR RESISTANCE TO SCALING 


AIR CONTENTS BY FOUR OTHER METHODS OF TEST 


Numerals upper right corner of slabs indicate rating of surface: 
0 - No scaling 3 - Moderate scaling 


1 - Very slight scaling u - Moderate to bad scaling 
2 - Slight to moderate scaling 5 - Bad scaling 


Lab.Ground Cem Commercial Portland Cements 


With s ae 
ith Natural Wood With = = Cc 
Resin and Tallow Natural Wood Resin ae 6 sacks per cu. yd. & @ 
a ~ 

5 1600 . DS 80 Mod. of Rupture : 
Ps ao 5 a e 
15 S Qe Comp. Strength— 
=. ¢ _ =o 
Q - re) Bd ~Mod. of Rupture” 1200 © c 60 
& 05 o) ; bpm lyeay fe) & 
x i= : Sw ee 

0 a s00 “40 

co) ~ 
-80 = oad 

BS B g 8 
us -60 S 4005 ow 2 
i= oe ae 
s B40 5 2 is 6 sacks percu.yd. 
9-20 0 a  Y 
. _ 0 2 4 6 8 
a 
2 Air Content of Fresh Concrete- per cent by volume 


nD 
ro) 


FIG. 8 - STRENGTH RELATIONS FOR CONCRETE CONTAINING NATURAL WOOD RESIN 
ADDED _IN A NaOQH-WATER SOLUTION AT MIXER 


a 


Plotted compressive strengths are the average for three 6xl2-in, concrete 
cylinders; plotted values of modulus of rupture are the average for 
three 3x3xlld-in, concrete prisms loaded at center of 10-in, span. 

Aggregate: Elgin sand and gravel graded from 0 to l-in, 

Cement Content: 4, 5, 6 and 8 sk.per cu, yd. unless otherwise noted, 

Slump; 3 to 4 in, 

Specimens cured in moist room, tested damp, 


Loss in Wt-% 
So 


Series 3u1 


Air Content of Fresh Concrete -% by volume 


1 T= RESULTS OF FREEZING AND THAWING TESTS OF 3x3x11}-IN. CONCRETE PRISMS 
CONTAINING CEMENTS GROUND WITHOUT AND WITH TALLOW OR NATURAL WOOD RESIN 


ed values are for 225 cycles of freezing and thawing, 


d: O Concrete made with cements without addition, 
A Concrete made with cements ground with tallow used alone and 
blended with cement without tallow. 
@ vodcreve made with cements ground with natural wood resin used 
alone and blended with cement without natural wood resin. 


ete; Cement content 6,3sk, per cu. yd,; slump 2 to y-in. After one day in 
molds prisms cured in water for 13 days,1 month in air of laboratory 

~ a 2 to 5 months in sealed metal cans, Prisms than soaked in Water 

or 7 days and frozen and thawed immersed in a 10% calcium chloride 
pba oe 4 bees lb given an additional 125 cycles while 

n tap water unless scontinued bef 

Mt ne 250 cbeles’ u efore they had received a 

Series 1-327, 
3/22/44 


2000 


1800 
S 
5 =siG00 
2 
O 
= 
AS, 
9) 
& 311400 
= 
XO 
oy= 
a: 
i — 1200 
Ou 
mo 
=m 
a2 1000 
= 
2S 
© 800 
2 
ee 
ae 
2 > 600 
v 
pag) 
= 
Oo 
a0 
Lv 
UO 
Bp 
O 
200 Legend — « Non Air Entrained 
------s 4-4 0 Air Entroined 
ol. 2 
0 | 2 S & 5 6 


Air Content - Percent 


Fig 9-Effect of Air Entrainment on the Resistance of Concretes 
to Freezing and Thawing 


Specimens cured 28 days moist and 3 days in water prior to freezinc 


6-/9-J5/ 
ASAE Pe 


17T #+€6 


APRIL & 1952 


Fig. 10- The box on the right shows the benefit of air-entrained concrete in resisting severe 
weathering. Except for the air-entrainment the two boxes were similarly constructed. 
Both were made with a lean mix of high slump. 


Fig. ll - First stage of deterioration, Fig. j2- More advance stages of 
"D" cracks forming at inside slab deteruoration.) “"b" cracking 
corners. has extended into body of slab. 


Research and Development Laboratori 
Portland Cement Association ein 
Chicago 


Approximate Cement Content per Cu.Yd. of Concrete 


64 sk. Normal 54 sk. Normal Portland | 63 sk. Portland with 
WITHOUT ENTRAINED AIR WITH ENTRAINED AIR Portland plus 94 1b. Natural 


Fig. 13 - CONDITION OF TYPE II CEMENT (6.5% C,A) CONCRETE 
BEAM SPECIMENS AFTER 5S YEARS’ EXPOSURE TO AN ALKALI SOIL 


50 Cycles 300 Cycles 
Rating of surface condition shown in circles. 
Calcium chloride applied to ice frozen on top surfaces of 3x6x15-in. 
slabs from Maine Project F.A.118AB. 


FIG, 15 - VIEWS OF TOPS OF CONCRETE TEST SLABS AFTER 
50 _ AND 300 CYCLES OF FREEZING AND THAWING 


Type [A Cement, Lot 17442 


-6 


Modulus of Plasticity - Sonic Method 
lb.per sq.in.x 10 
Linear Expansion - per cent 


300 
Cycles of Freezing and Thawing  5..,., 7218 


Air Content of Fresh Concrete -per cent 


CEMENT AIR IN CONCRETE 
A-Norm, Portland 0.8% 
B-Norm,Portland plus Plain Natural "x" 1.3% 
C-Norm,Portland plus Plain Natural "y" 1.5% 
D-Norm,Portland plus Natural "X" with Tallow 4.5% 
E-Norm,Portland plus Natural "Y" with Wax Dist, 3.1% Coloring Agent - per cent 
Prisms frozen and thawed in tap water, Mix 1-2.4-3.4 by weight. 
Blends; 5 portland plus 1 natural cement by weight, Tests made FIG, 16 = EFFECT OF COLORING AGENTS ON 


in Research Laboratories of the Portland Cement Association, THE AIR CONTENT OF CONCRETE 


Fig, 14 - LINEAR EXPANSION AND REDUCTION IN MODULUS OF ELASTICITY 


(SONIC METHOD) OF 2x2x94-IN, CONCRETE PRISMS DURING 
FREEZING AND THAWING 


<a lie lemma 


Air Content of Concrete - % 


Research and Development Laboratories 
Portland Cement Association 
Chicago 


(100% Mortar ) Cement Content - 4 sks /cu. yd. 


Slump -2 to 3 inches 


(76%) 


°(6/%) 
Type [A + Air-Entraining Agent 


Air Content of Concrete -% 


O 
No.4%Zin. %in. yin 2\4in. 
Maximum Size of Aggregate 


(100% Mortar) Cement Content-53 sks. (cu. yd. 


Slump -2 to 3 inches 


Cement Content - 7 sks./cu. yd. 
Slump _- 2 to 3 inches 


(60% 
ioe LA+ A-E. Agent 


No.4 %in.  3fin. | Ain. Zin. _ No.4 %in. >in. Ain. 2Kin. 
Maximum Size of Aggregate Maximum Size of Aggregate 


Fig. 17 —- Relationship Between Maximum Size of Aggregate and 
Air Content for Concretes of Constant Cement Content 
and_ Consistency 


Elgin, Illinois, sand and Eau Claire, Wisc. gravel. 


Figures in parenthesis are the average mortar contents 
of the concretes made with the particular 
maximum size of aggregate. 


Serves G67 
/1-16 -5/ 
Fath Pe 


Research and Development Laboratories 
Portland Cement Association 
Chicago 


Ss SHS ACUAOC ® 2 to 3 in. Slump 


USK Sa / CULO. 2 fo Zin. Slump 


Net Water- Cement [Ratio - gal. per sk. 
Nef Water -Cement. Ratio — gal. per sk: 


: 


eee 


paath 


Cement Content — 4sks./cu. yd 
SMT) Pa CVO IT AGNES 


ey Deo i We pa o” 2 4°56 .6 jo (aia 
Air Content of Concrete - % Air Content of Concrete -% 


Fig.18- Effect of Air Content on the Water Requirement 
of Concretes of Constant Cement Content 
and Consistency Made With 
Various Maximum Sizes of Aggregate 


Elgin, Illinois, sand and Eau Claire, Wisc. gravel. 


Serves 367 
H=-S9- Sf 
P.K. 


Third point loading - I8-in. Span 


Modulus of Rupture -Ib. per sq, in. 


Modulus of Rupture Compressive Strength 


600 g000 
Age ® 4000 saws 
a 
200 oon 
0 =i) Pe Maximum Size of Aggregate-23in. 
oO 
> 6000 
s) 
2 4000 
Cc 
“1 2000 
Oo 
0 


No. + 
fae eAmNcHnBm 10.120 14 ni6 
Air Content of Fresh Concrete -% 


no 
pane 


Ce ee OM Ome Cea. anlG 


Fig.19- Effect of Entrained Air on the 28-day Strengths 
of Concretes of Constant Cement Content and Consistency 
Made With Various Maximum Sizes of Aggregate 


Cement Content: 4 sks. percu.yd. Slump: 2 to 3 inches. 
Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel. 
Cements: Typel, Type IA, and Type IA+Natural Wood Resin. 
Curing: Continuously moist cured. 


Ser/es 367 
IS ee 
PK. 


Third point loading - [8-in. Span 


Modulus of Rupture -lb. per sq. in. 


Research and Development Laboratorics 
Portland Cement Association 
Chicago 


Modulus of Rupture Compressive Strength 


Maximum Size of Aggregate -23in. 


6-in. Modified Cubes 


2000 

0 
6000 
6000 
4000 


pressive Strength - lb. per sq. in. 


3% 
gf). 
| 0 
6000 
E 000 
CS Te I 
2 2000 
al No. 4 No. 4 
) 
"0 2) nC cae 0 2.4 6.8 [0 Ic anne 


Air Content of Fresh Concrete-% 


Fig.20- Effect of Entrained Air on the 28-day Strengths 
of Concretes of Constant Cement Content and Consistency 
Made With Various Maximum Sizes of Aggregate 


Cement Content: 5% sks. per cu.yd. Slump: 2to 3 inches. 
Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel. 
Cements: Type |, Type IA, and Type IA+Natural Wood Resin. 
Curing: Continuously moist cured. 


Serres 367 
J!- 21-5] 
PERG 


Research and Development Laboratories 
Portland Cement Association 
Chicago 


Modulus of Rupture Compressive Strength 


pres 


Max. Size of Aggregate 2-0 Max. Size of Aggregate - 23-in. 


Third Point Loading - 18-in. Span 
Modified Cubes 


Modulus of Rupture -Ib./sq. in. 
6-in. 


Compressive Strength —Ib./sq. in. 


800 8000 

600 6000 

400 4000 

200 2000 
oa a 


lo (2 14 16 OO. "12 
ap Content of ana aoe 


Fig. 21 - Effect of Entrained Air on the 28-day Strengths of Concretes 
of Constant Cement Content and Consistency Made With Various 
Maximum Sizes of Aggregate 


Cement Content: 7 sks./cu.yd. Slump: 2 to 3 inches 
Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel 
Cements : Type I, Type IA and Type IA+Natural Wood Resin. 
Curing : Continuously moist cured. ae 


10-26-S/ 
PK, 


Expansion During 300 Cucles of Freezing and Thawing - % 


Expansion During 300 Cycles of Freezing and Thawing -% 


Research and Development Laboratories 
Portland Cement Association 
Chicago 


Discontinued 


+ tt tO eet { 
Oo ex A A 


{j—_~> 


4 sks. per cu yd 
2 10 DA PRSTULIO™ 


Max. Size of 
Aggregate 
No. F- 

ce 


(23 45-5) G7 8! 9 OT II Ze Seem iG 
Air Content of Concrete — % (Pressure) 


Discontinued 


Se sks. per cu. yd. 
BOSS A1 ie SIT ime 


Max. Size Aggregate 
No. F EOS 


I 2 SRV So 6 7 @- Be SMO mia Ie Hiaiis 
Air Content of Concrete —% (Pressure) 


Expansion During 300 Cycles of Freezing and Thawing - % | 


Discontinued 


7 sks. per cu.ya 
2 fo 3-in._s/ump_ 


Aggregate No. ¢ 


0 
O12 3 4 5 6 7 6 9 IORIRNICST sae 


Air Content of Concrete - % (Pressure) 


Fig.c2— Expansion of Concretes 
During 300 Cycles 
of Freezing and Thawing 


Curing: Iday in molds, I3 days in 
moistroom, 14 days in the air 
of the laboratory and 3 days 
in water prior to start of 
freezing and thawing tests. 


Specimen: 3 by 3 by 114-in. prism. 


Frozen and thawed while immersed 
in tap water, two cycles per day. 


Aggregate: Elgin, Illinois sand and 
Eau Claire, Wisc. gravel. 


Ser/es 367 
10-23-S5/ 
PR. 


Research Laboratories of the 
Portland Cement Association 
33 W. Grand Ave, Chicago, !0 


Type IA Cement (Agent A_) Lot /7696 
Lancitick SWil2 Mixer 


Air Content Before Vibration 


Air Content After Vibration (External) 
Sir Content Before Vibration jt Ome on a Once “ 
ON 


— — . 


oO 
2S oa 


t Air Content After Vibration KL 5 
(External) Air Content Affer Vibration (Internal) 


e 
Air Content After Vibration (/nterna/) 


: Type _IA Cement (Agent 8) Lot 17780 
ancirick SW /I2 Mixer 


Type_/A_Cement (Agent B) Lot /7780 


Tilting Orum Type Mixer i 


Air Content Before Vibration” 


Air Content After Vibration (/nterna/) 
Air Content Affer Vibration 
(Internal) 


=I. 


4 5 6 7 8 9 lo oO | 2 3 4 
Slump - inches 


Fig.23-Effect of Slump and Vibration on the Air Content of Fresh Concrete 


Mix by Wt.: I-2.26-3.68 | Nominal Cement Content: 6 sks. per cu. yd. 


Elgin Sand: O-No.4 
"Gravel: No.4-I3-in. Mixing Time: 3 min. Period of Vibration: 3 min. eae 
/-4-48 


in Air Content — Per cent 


Reduction 


Research and Development Laboratories 
Portland Cement Association 
Chicago 


Type IA Cement (Agent A) Lot /7696 
Laneirick SW/2 Mixer 


| 


Type 1A Cement (Agent 8) 
Lot 17780 


Type IA Cement ( Agent A) ) 
Lot /7696 


oO 


Internal Vibration 


<é Externa/ Vibration Pe een 


Sa ie 
== i Elgin Sand :0-No.4 


4 Elgin Gravel : No.4 to I¢-in. 


_12/.slump, 


Nominal Cem. Content : 6 sks. /cu.yd. z= = 
wc : 450/ Gal Be) eh i 

/UMp Pais 2.9 a <F 
Mixing Time : 3minutes 4 a 
Initial Air Content: 42% OD ae 


Air Content by Pressure Method ~ per cent 
Qo 


2 
Type [A Cement (Agent 8) Lot /7780 
Lancirick SW/2 Mixer 
(6) 
40 60 80 100 120 40 60 80 100 120 
Temperature of Concrete -°F. 
Internal Vibration Ue ees Fig.2&-Effect of Temperature on fhe 
a ai . 
[os — Air Content of Fresh Concrete ae 
/~- 7-48 
Cay Elgin Sand :0-No.4 
External Vibration Elgin Gravel : No.4 to /#-/n, 
Nominal Cem. Content :6 sks /cu.yd, 
w/c: 5.0/ Gal per sack 
Slump 1 2.9-3.5-in. 
Mixing Time . 3 minufes 
Initial Air Content : 6% 
0 
0 2 ©) 4 5 6 Z 8 9 10 
Duration of Vibration — Minutes 
Fig.24-Effect of Duration of Vibration on the 
Air Content of Fresh Concrete 3-4 inch Slump 6-7 inch Slump 
: Series 336 © 6 sk. cement per cuyd | © 6 sk. cement per cu yd. 


/-8-¢48 o 5sk. cement per cu. yd | 0 Ssk, cement per cu yd. 


t 
010% Agent A 


Elgin Sand = :0O-No.4 

Elgin Grave! :Na4 to /#-in. 
S/ump Be = S)Hoh 

Nom. Cement Content: S# sks. 
Lancirick SWi2 Mixer 


t 


-0075% Agent A 


Air Content - Percent 


Type IA Cement, ( Agent A ) 
ik Lot 17696 


{50% Type IA Cement (Agent A) 
Blend {50% Type IA Cement (Agent 8) 


| | 


JA Cement, (Agent B) _ 


Air Content by Pressure Method —per cent 


22 26 30 34 30 42 22 26 “30. eotee somes 
Sand Content - Percent 
Y we} be a ee eee Cons el Fig.Z-Effect of Percentage of Sand on Air Content of Concrete 
Time of Mixing — Minutes 


Fig.26-Effect of Mixing Time on Air Content 
of Fresh Concrete 


Series 336-3 
/-7-48 


Printed in U.S.A. | 


j ‘ 
' 


ant. i fl 


S 


RISA (AM 
Sa 


GS7rs 


P-FATEF 


Copyright 1957 by Portland Cement Association 


This prosperous farming area north of Ogden, Utah, near the site of irriga- 
tion’s start in America 110 years ago, is served efficiently and dependably by 
the concrete-lined Ogden-Brigham Canal. 


Lining Irrigation Canals 


Foreword 


Modern irrigation in America dates back to 
July 1847, when the Mormon pioneers diverted a 
creek to irrigate a portion of what is now Salt Lake 
City. By 1900 most of the West’s obvious, easy and 
low-cost diversions for irrigation had been accom- 
plished, and over eight million acres were being ir- 
rigated. The Reclamation Act, which became law 
in 1902, provided that the United States could con- 
struct economically feasible irrigation projects if the 
people benefiting from them would agree to repay 
their cost. Thus the federal government officially 
recognized that agricultural development of the West 
is in the interest of the country as a whole. This 
made possible the construction in the arid West of 
projects that were beyond the financing capability 
of individuals, water districts and even the states. 
In recent years irrigation has spread to the more 
humid eastern states as well. 


Irrigation systems should be built in such a 
way that they operate at maximum efficiency. It is 
very important to store, transport and use the avail- 
able water without undue loss through evaporation or 
leakage. Often, lining irrigation canals to prevent 
seepage losses, which average 40 per cent of the 
water transported in unlined canals, is justified on 
a purely economic basis. Certainly the loss of this 
valuable water cannot be tolerated indefinitely. 

This booklet tells why irrigation canals need 
lining and how to determine the most economical 
type of lining. It describes the types of lining most 
commonly used today, and outlines procedures for 
their design and construction. This information 


should be of value to irrigators, investment bankers, 


engineers, public officials and others interested in 
irrigation and the conservation and development 
of our water resources. 


Aerial view of the Columbia Basin in 
the vicinity of Quincy, Wash. (center 
background), taken in July 1952, 
shows the recently completed con- 
-crete-lined West Canal and, to its 
right, three main laterals to which 
water is pumped from the canal. 
Note that only a few patches of land, 
to the left of the West Canal, are un- 
der cultivation at this time. 

Courtesy of Bureau of Reclamation. 


A view of the same section of the 
Columbia Basin project taken two 
years later, in September 1954, 
shows how the availability of water 
has transformed barren lands into 
productive cultivated fields. 

Courtesy of Bureau of Reclamation. 


Table of Contents 


TVEPOGUICELION ater eee en ee at es een re SL ene 
1. Why Irrigation Canals Need Lining.......... 5 
Pee CONGMOICS Of; anal alain ng eee en) ed 11 
3. General Design Considerations............... 14 
4, Cast-in-Place Concrete Linings.............. 19 
5. Shotcrete Linings - Wiis 26 
6. Soil-Cement Linings . : ee CUNO ge Rares 29 
7. Other Uses of ona in Irrigation : ee IESO 


eee 
t, 


The activities of the Portland Cement Association, a national organi- 
zation, are limited to scientific research, the development of new or 
improved products and methods, technical service, promotion and 
educational effort (including safety work), and are primarily designed 
to improve and extend the uses of portland cement and concrete. The 
manifold program of the Association and its varied services to 
cement users are made possible by the financial support of over 
70 member companies in the United States and Canada, engaged in 
the manufacture and sale of a very large proportion of all portland 
cement used in these two countries. A current list of member com- 
panies will be furnished on request. 


Introduction 


the value of irrigation 


America is a relatively new country, but it has 
a long history of irrigation, dating back to the 
Indians who inhabited our continent before Colum- 
bus ‘“‘discovered”’ it. These early residents of the 
southwestern United States, Central America and 
portions of South America recognized the value of 
irrigation, as evidenced by the ruins of irrigation 
canals and structures in those regions. Large areas 
in Asia and Africa have still longer records of suc- 
cessful and profitable irrigation. 

Since the beginning of America’s modern ven- 
ture into irrigation, about 110 years ago, some 27 
million acres have been placed under irrigation. 
Twenty-five million of these acres are in the 17 west- 
ern states and can be classed as arid or semiarid, 
where rainfall clearly is insufficient to support dry- 
land farming. In other parts of the United States, 
where rainfall is more abundant during the year, 
irrigation is receiving more and more attention as 
insurance against crop failure from lack of moisture 
at critical times. Each of three southern states, 
Arkansas, Louisiana and Florida, has over half a 
million irrigated acres and is increasing the area 
under irrigation each year. 

Irrigation as we know it today is not a costly 
experiment but a proven asset. The most obvious 
indication of this is the considerable increase in the 
value of land with access to irrigation water over its 
value as arid desert or even as unirrigated farm land 
in a humid area. Benefits from irrigation accrue to 
the individual, the local community and the nation 
as a whole. Local farm and nonfarm income result- 
ing directly from the irrigation of an area far exceeds 
the total gross crop return to the irrigator. Nation- 


Furrow irrigation in Arizona’s Salt River Valley, typi- 
cal of thousands of acres in this area being irrigated 
from concrete-lined canals and ditches. 


Furrow irrigation of cotton field in Jackson 
County, Ark. 


Courtesy of Soil Conservation Service. 


wide, the crops and livestock produced in an irrigat- 
ed area create income in transportation, processing, 
manufacturing, wholesaling, retailing—in short, at 
all points of handling between the producer and the 
ultimate consumer. On the other hand, the reverse 
process of supplying the clothing, household appli- 
ances, farm equipment and other products required 
and demanded by the irrigator benefits the national 
economy. 

The Salt River Project in Arizona, one of the 
first to be constructed under the federal Reclama- 
tion Act, is an ideal example of the benefits of ir- 
rigation to the local community and also to the 
nation as a whole. In 1910 Phoenix was a village in 
the desert, and Maricopa County, which includes 
most of the project’s producing area, had 15,000 
irrigated acres and about that many inhabitants. 
Today the county’s population is 500,000, and its 
300,000 irrigated acres constitute one of the most 
productive agricultural areas in the country. Not 
only has this project’s entire federal loan of $26.7 
million been repaid by the water users, but the fed- 
eral treasury currently is receiving an estimated 
$175 million annually in taxes from this area. 

Probably the most important justification for 
irrigation is the fact that our country’s population 
is increasing at an unprecedented rate, without a 
corresponding increase in acres under cultivation. 
By clearing, draining or irrigating, many acres can 
be made productive. In the West and Southwest 
there is more arable land than there is water avail- 
able for irrigation. In the humid areas of the southern, 
eastern and midwestern states there are many acres 
under cultivation that could be made more produc- 
tive by supplemental irrigation. These facts point 
up the importance of conserving all water that car 
be used economically for irrigation. This requires 
not only the capture and storage of water but alsc 
its transportation to the land without undue loss 


Why Irrigation Canals Need Lining 


Experience has shown that irrigation of arable 
lands deficient in natural moisture is justified by 
the benefits that result. Similarly, the lining of an 
irrigation canal is justified economically when its 
cost can be repaid in benefits during the life of the 
lining. Some of the more important tangible bene- 
fits resulting from lining irrigation canals—those 
that can be evaluated with some accuracy—are sav- 
ings of water that would otherwise be lost through 
seepage, reclamation of waterlogged lands, lower 
maintenance and operation costs, and reduced right- 
of-way requirements. Some additional benefits from 
lining canals, such as prevention of bank erosion and 
breaks or better control and more uniform distribu- 
tion of water, are difficult to evaluate from a mone- 
tary standpoint but should be given consideration 
when the value of a lining is being appraised. 


linings reduce water loss 


The earliest irrigation canals were merely 
unlined ditches, and even today the great majority 
of all irrigation canals are unlined. Much of the 
water flowing in these canals is lost through seepage 
before it can be distributed to the crops. 

The number of acres that can be irrigated is 
determined by the amount of water available. Since 
only water applied to the land contributes to crop 


Seepage from this unlined canal is clearly evident. 
Often, however, seepage is not detected when the 
water percolates downward to a lower water table. 


raising, all losses in transit reduce irrigable acreage. 

Records of the Bureau of Reclamation and of 
independent irrigation districts indicate that, on the 
average, almost 40 per cent of the water entering a 
distribution system of unlined canals never reaches 
the farm ditches. This includes losses from evapora- 
tion, water transpired by uncontrolled vegetation 
in and near canals, unavoidable spilling and waste 
of excess water, and seepage. The latter is the 
greatest loss of all and in canals and laterals averages 
about 25 per cent of the total water diverted. Losses 
in some systems are as much as 60 per cent. In 
some areas the return flow of seepage water to 
natural drainage channels or its collection through 
drains makes possible its re-use, but in most cases 
it is permanently lost to the irrigator entitled to it. 

The rate of seepage from a canal depends largely 
on the permeability of the soil and the depth of 
water. The rate per unit wetted area would be 
greater for sandy loam than for clay loam and greater 
for a 2-ft. depth of water in the canal than for a 
1-ft. depth. Field-measured seepage rates generally 
are reported as cubic feet per square foot of wetted 
area per day or as the percentage per mile of the 
total volume of water flowing. Because of their rela- 
tively large ratio of wetted area to volume of water 
carried, small canals lose a larger percentage of water 


Irrigation labor is reduced when canals are lined with 
concrete. There can be no ‘‘breakouts’’ or seepage from 
this farm canal near E] Indio, Texas. 


per mile than do large canals. In unlined farm ditches 
carrying less than 5 cu.ft. per second (cfs) the seep- 
age losses probably average 20 per cent per mile, 
while for very large canals a rate of 1 per cent per 
mile is considered average. 

If all the seepage losses in main canals, laterals 
and farm ditches, which average at least 40 per cent, 
were prevented, it would be possible to irrigate 100 
acres for every 60 acres now under irrigation at no 
additional cost for water. In the years to come the 
increased acreage undoubtedly will be the most im- 
portant reason for lining irrigation canals. 

Several methods may be used to measure the 
loss through seepage in an existing canal. The pond- 
ing method, which involves isolating a section of 
canal by means of temporary bulkheads, filling that 
section with water and observing the decrease in 
volume over a period of time to establish the rate 
of loss, is the most accurate method. 

The inflow-outflow method, which is not as 
reliable as ponding, requires measuring the flow 
with Parshall flumes, weirs or current meters at 
the upstream and downstream ends of the reach 
being studied. A seepage meter is a device that 
isolates a small area of canal perimeter and meas- 
ures the water that seeps into the subgrade in 
that area. The seepage meter in its present stage 
of development is not an accurate means of measur- 
ing seepage. Its chief value probably lies in locating 
general areas of greater-than-average loss. 

The value of the water lost is not the only 
monetary loss that can be charged to seepage. The 
Bureau of Reclamation recently reported that, 
whereas the value of water saved through the in- 
stallation of canal linings from 1946 to 1952 was 
approximately $1.6 million, the value of adjacent 
farm land that was saved from waterlogging was 
over $2.2 million. The savings made by the canal 
linings in the Gering-Fort Laramie Irrigation 
District of the North Platte Project in Nebraska 
are typical. About 6,800 ft. of a lateral canal were 
lined with concrete in 1950. Seepage loss measure- 
ments made before and after the lining was placed 
indicate that at least 440 acre-ft. of water, valued 
at $900, are now saved each year. More important 
is the fact that 740 acres of land that had been 


Gophers and other animals, such as 
the crawfish shown here, burrow 
through the banks and bottoms of 
unlined canals. A hole like the one 
in this canal always results in the 
loss of valuable water and may be 
enlarged to the point where the en- 
tire canal is endangered. 

Courtesy of Bureau of Reclamation. 


waterlogged have been reclaimed and are back in 
production, while an estimated 300 additional acres 
that were threatened with waterlogging have been 
saved. The value of this land is about $185,000, 
while the cost of the lining was only $32,500. The 
economic justification in this case is obvious. 

Drainage systems to remove excess water from 
the surface or subsoil are necessary in some irrigated 
areas. Such systems are concerned both with the 
disposal of precipitation runoff and irrigation waste 
water and with the removal of groundwater, which 
usually is the result of seepage from irrigation canals 
and ditches. Lining these canals and ditches would 
reduce the quantity of seep water that has to be 
handled and consequently reduce the size and cost 
of the drain ditches, conduits and other drainage 
facilities. 


concrete linings 
prevent canal failures 


While it may be possible to lay out an unlined 
canal on grades that would provide uniform flow, 
in actual practice variations in velocity are inevita- 
ble. Experience has shown that where the velocity 
of flow in unlined canals varies, some scouring or 
deposition of material is bound to take place. In a 
concrete-lined canal erosion is no problem, and the 
small quantities of materials that may be trans- 
ported into the lined section can be readily removed 
without damage to the lining. 

Canal breaks are expensive at any time, but if 
one occurs when water is needed for crops the loss 
in crop production probably will be greater than the 
cost of repairing the canal. Such a possibility should 
be considered when evaluating the benefits and 
advantages of concrete-lined canals. There are in- 
stances on record where small breaks in unlined 
canals resulted in washing away considerable por- 
tions of embankment. In most cases the damage to 
crops as a result of the canal being out of service 
at a critical time was greatly in excess of the cost 
of repairing the canal. Burrowing animals, which 
are frequently the cause of these costly breaks in 
unlined canals, cannot penetrate concrete. 

Protection of the canal against bank erosion 
and breaks is particularly important when it is 


located on the side of a hill, as many canals must 
be. On the basis of service experience with concrete 
lining in such locations, the Bureau of Reclamation 
has, in recent years, lined its sidehill canals with 
concrete in the Columbia Basin, Central Valley, 
Colorado-Big Thompson and other projects. Resi- 
dents in the areas below these lined canals can be 
confident that disaster will not strike as a result of 
a small canal break quickly enlarging itself to per- 
mit catastrophic spilling of the water. 


concrete linings 
reduce maintenance costs 


The removal of weeds and plants from unlined 
irrigation canals is a major annual maintenance 
activity. Lining the canals with hard-surfaced, im- 
penetrable concrete practically eliminates the ex- 
pense of weed and plant removal or control. 


Maintenance of weed-grown canals like this is very 
costly. Weeds and bank irregularities reduce capacity 
and increase danger of overtopping. 


For a canal located high on a hill- 
side, concrete lining provides insur- 
ance against minor breaks and ro- 
dent holes that might cause the 
canal bank to be washed out and 
endanger life and property below. 
Horsetooth Feeder Canal near Love- 
land, Colo. 


Courtesy of Bureau of Reclamation. 


This photograph taken in 1956 shows a portion of 35 
miles of canal lined with 214-in. concrete in 1938 by 
the Hidalgo County Water Control and Improvement 
District No. 2, San Juan, Texas. The orchard to the 
right is on part of the 3,000 acres of reclaimed land 
that was waterlogged before the canal was lined. 


The repair and reshaping of the canal section 
is another annually recurring operation for most 
unlined canals. This work is particularly costly 
where the soils are friable, where there is consider- 
able curvature, or where the water has a high veloc- 
ity. Areas that have been scoured or eroded must 
be rebuilt, and where sediment has been deposited, 
as at bends or structures, it must be removed. 

Determination of average annual maintenance 
costs for irrigation canals is not easy. The cost of 
maintaining an unlined canal may be quite nominal 
for the first few years after construction, but the 
major cleaning and repair job that ultimately be- 
comes necessary raises the average to a much higher 
figure. The cost of maintenance varies considerably 
between projects because of such factors as climate, 
period of operation, topography and conditions of 
service. On the basis of available records, the Bureau 
of Reclamation in 1952 estimated maintenance costs 
for canals carrying at least 100 cfs to be about 75 
per cent more for unlined or earth-lined canals than 
for concrete-lined canals. In some locations the 
annual cost of maintaining small unlined farm ditches 
approaches the initial cost of lining those ditches 
with concrete. 


concrete linings 
cut irrigation costs 


When canals, laterals and farm ditches are 
lined with concrete the water available may be 
distributed easily and economically to the water 
users as planned. In these days of labor scarcity and 
high wages irrigation district managers and individ- 
ual farmers are using every possible means to cut 


The Franklin County Canal, near Pasco, Wash., was 
lined in 1923 with pit-run concrete. It is still in good 
condition and has required little maintenance since 
its construction. 


their expenses by reducing labor requirements. 

One farmer near Eagle Pass, Texas, has seven 
miles of concrete-lined ditches to irrigate 800 acres. 
This lining has reduced the labor necessary for ir- 
rigation more than 75 per cent. Two men now irri- 
gate five acres an hour, whereas previously eight 
men were required. 

The farms on the Fort Sumner, N.M., irrigation 
project offer an excellent example of the efficiency 
that can be attained through use of concrete-lined 
laterals and farm ditches. Some of these farmers 
have devised and built systems that are practically 
automatic. One 155-acre farm has been so well pre- 
pared for irrigating that, after the ditches were lined 
with concrete, it could be irrigated with a minimum 
of labor and trouble in less than 24 hours. As an 
average the concrete-lined ditches on this project 
are saving the farmers up to one-half of their irri- 
gating time and at least one-third of the water. It 
is conservatively estimated that the saving in water 
and labor will pay for the lining in about five years. 


concrete linings increase capacity 


Resistance to the flow of water in a canal with 
a smooth lining of concrete is much less than in an 
unlined canal. Consequently the velocity of the 
water can be much greater. Since concrete has 
proved its ability to withstand high velocities with- 
out appreciable wear, it is frequently possible to 
take advantage of steep slopes to convey large quan- 
tities of water in a relatively small lined waterway. 
This would be impossible in an earth canal, since 
velocities over 2.5 or 3.5 ft. per second, depending 
on the type of soil and size of canal, would soon 
result in damaging erosion. 

The chief engineer of one large irrigation dis- 
trict estimated that if the canals and laterals of his 
district were lined, approximately one mile of every 
eight could be eliminated by minor relocations to — 
steeper, more direct routes. 

Table 1, with the accompanying diagram, 1l- 
lustrates the comparative efficiency of concrete- 
lined and unlined irrigation canals. The calculations 
were based on the assumption of identical gradients 
(s) and carrying capacities (Q). Manning’s formula* 
for computing the flow in open channels was used 
to make the necessary calculations. The coefficient 
of roughness (n) for concrete-lined canals was taken 
as 0.014 and for unlined canals as 0.025. Comparison 
of the required top widths (W) shows that a lined 
canal requires appreciably less land area than an 
unlined ditch of equal capacity. 


*Manning’s formula is 
Hs Ae SYRY, 


in which 
v = velocity in feet per second; 
n = coefficient of roughness; 
S = slope; 
R = hydraulic radius. 


High velocities cannot damage this 
concrete-lined chute on the South 
Branch Canal, near Ellensburg, 
Wash. Lining was placed about 1926. 


Table 1. Comparative Dimensions of Concrete-Lined and Unlined Canals 


Concrete-lined Unlined 
n=0.014 n=0.025 


Approximate 
capacity, 
Hp Q, 
ft. : : cfs 


Excavation costs also are materially greater for 
unlined than for concrete-lined canals. Where cuts 
are deep, the saving in excavation would pay for 
a concrete lining. 


concrete linings 
protect public health 


It is a well-known fact that mosquito propaga- 
tion is a problem associated with unlined drainage 
canals and ditches. Although mosquito-borne ma- 
laria and yellow fever have been practically elimi- 
nated, the problem of encephalitis (sleeping sick- 
ness) remains to be solved. This disease results from 
infection by mosquito-borne viruses and can cause 
serious brain damage or death. 


Apart from disease transmission, mosquitoes 

interfere with human comfort and welfare. 

Among the causes for mosquito production as- 

sociated with unlined irrigation canals are: 

1. Seepage, which creates swampy areas. 

2. Canal bottoms not on true grade, which causes 
ponding during non-use periods and weed 
growth. 

3. Tules, cattails and other weeds growing in 
unlined canals, in which mosquitoes prefer to 
lay their eggs. 

With concrete linings, conditions that are conducive 
to mosquito propagation are not likely to occur, 
since seepage and ponding are reduced and weed 
growth is eliminated. 


Lining this canal through the rock cut with smooth concrete permitted a reduction in size. This effected a saving 
in excavation costs, which more than paid for the lining. Heart Mountain Canal, near Cody, Wyo., lined in 1937. 
Courtesy of Bureau of Reclamation. 


Economics of Canal Lining 


The true cost of a lining is not its first but its 
annual cost. The annual cost includes annual depre- 
ciation and interest charges during the life of the 
lining. The average annual depreciation of a lining 
is determined by dividing the construction cost, less 
salvage value, by its life expectancy in years. In- 
terest charges can be reasonably approximated by 
multiplying the annual interest rate by the first cost 
of the lining plus the salvage value at the end of its 
life expectancy and dividing that product by 2. 

The annual benefits accruing from lining a canal 
must be greater than its annual cost if its construc- 
tion is to be justified. The annual cost of lining will 
vary with the type of lining. The most desirable 
type would be the one with the lowest annual cost. 
Since first costs are not the same in all localities, 
annual costs will be different and a cost analysis will 
be necessary for each location. Form A, page 12, 
will be helpful in determining which of two types of 
lining has the lower annual cost and therefore is 
the more economical. 

In the case of original construction, it is nec- 
essary to compare the additional annual cost of a lined 
Over an unlined canal with the annual benefits de- 
rived from lining. Form B, page 12, can be used for 
this purpose. If a lining is being considered for an 
existing canal, Form C, page 13, should be used 
instead of Form B. Form D, page 13, is suggested 
as a guide in computing annual benefits. 

In a comparison of the annual costs of two 
types of linings, on Form A, the annual maintenance 
charges are included. On Forms B and C, the annual 
maintenance charges are not considered in the an- 
nual cost, since the saving in maintenance cost of a 
lined over an unlined canal is included as a part of 
the annual benefits on Form D. 

Major economies in construction are possible 
when concrete lining is planned and placed at the 


time of the original canal construction. Unlined or 
earth-lined canals require much larger cross-sec- 
tional areas than concrete-lined canals of equal ca- 
pacity. To prevent damagingly high velocities un- 
lined canals usually are built wider, shallower, and 
with flatter side slopes than are lined canals. When 
it subsequently becomes necessary or desirable to 
line such a canal, the engineer is forced to choose 
between constructing an unnecessarily large lining 
in the existing canal or backfilling and reshaping the 
canal to accommodate the more efficient concrete 
lining. Either alternative is almost always more 
costly than if a properly designed concrete-lined 
canal had been built in the first place, because 

1. Less right-of-way would have been required. 

2. Excavation quantities would have been less. 

3. Drainage, diversion and storage facilities 

could have been of smaller capacity. 

4. Bridges and other crossings could have been 

shorter. 

It is extremely important that the lining of a 
main canal be carefully considered at the time of its 
planning and construction. Once an unlined main 
canal is placed in operation, it is almost impossible 
to shut off the water for the length of time required 
to line the canal. Therefore, in addition to the cost 
of reshaping the canal to a smaller cross-section, 
there may be the expense of constructing temporary 
bypasses to carry irrigation water during reconstruc- 
tion. These added costs may well exceed the cost of 
the lining itself. All these factors emphasize the im- 
portance of weighing the need for linings carefully 
in advance, and, if they are needed, of including 
them in the original construction. When considering 
the need for linings, the Bureau of Reclamation and 
other canal building agencies use field and laboratory 
tests to locate areas of probable seepage and to esti- 
mate its rate and magnitude. 


11 


12 


gt Aaa 


8 


For Comparing Estimated Annual Costs of Two Different Types of Linings 


. Annual interest charge: 


. Excavating, filling, compacting and trimming 
. Lining 
. Checks, turnouts, bridges and other necessary 


structures 


. Incidental construction 
. Total construction cost: (1) + (2) + (38) + (4) 
. Life expectancy: Type I______ years 


Type II]____—— years 


. Salvage value at life expectancy 
. Total depreciation during life: (5) — (7) 
. Annual depreciation charge: (8) + (6) 


(5) + (%) 
2 


. Annual maintenance charge 
. Total annual cost: (9) + (10) + (11) 


x interest rate 


A 


a 


PR PA ARPA HP 


Type I 


For Estimating the Additional Annual Cost of a Lined 
Over an Unlined Canal (Original Construction) and Net Annual Savings 


b. Unlined 


oon mD 1 > 


. Excavating, filling, compacting and trimming 
. Lining 
. Checks, turnouts, bridges and other necessary 


structures 


. Incidental construction 

. Total construction cost: (1) + (2) + (8) + (4) 
. Difference in construction cost: (5a) — (5b) 

. Life expectancy: _____ years 

. Salvage value at life expectancy 

. Total depreciation during life: (6) — (8) 

10. 
ids 


12. 


Annual depreciation charge: (9) + (7) 
Annual interest charge: Oo X interest rate 
Total annual cost: (10) + (11) 


Net Annual Savings 


13. 
14. 
15. 


Total annual benefits: (20), Form D 
Total annual cost: (12) above 
Net annual savings: (13) — (14) 


RRP LR A 


PRP RRP HK 


a. Lined 


PRA RPK 


AR 


Type II 


Form D 


For Estimating Annual Cost of Lining an Existing Canal and Net Annual Savings 


. Excavating, filling, compacting, reshaping and trimming 

. Lining 

. Checks, turnouts, bridges and other necessary structures 

. Incidental construction 

. Total construction cost: (1) + (2) + (38) + (4) 

. Life expectancy: ______ years 

. Salvage value at life expectancy 

. Total depreciation during life: (5) — (7) 

. Annual depreciation charge: (8) + (6) 

(Ore) 
2 


ooOnrio»rr wow r 


x interest rate 


a 
j=) 


. Annual interest charge: 


11. Total annual cost: (9) + (10) 

Net Annual Savings 

12. Total annual benefits: (20), Form D 
13. Total annual cost: (11) above 

14. Net annual savings: (12) — (18) 


For Estimating Annual Benefits from Lined Canal 


Land Saved 
1. Right-of-way, unlined canal peer aACTeS 
2. Right-of-way, lined canal - fete ee ee ACTES 
3. Right-of-way, saved: (1) — (2) eee eee eer acres 
4. Reclaimed waterlogged land ess ee rc Tes 
5. Total land saved: (3) + (4) us, ae te ee CTES 
6. Annual value of total land saved:______acres at $_____ (net crop value) 

Water Saved 
7. Flow when in use:____cfs 
8. Hours in use:______per year 
9. Total flow per year: (7) X (8) X 0.0826 =____acre-ft. 

10. Estimated loss from unlined canal:______% of (9) =_________acre-ft. 

11. Annual value of water saved:____acre-ft. (10) at $________per acre-ft. 


Maintenance Saved (Include maintenance of necessary drainage facilities.) 
12. Annual maintenance cost, unlined canal 
13. Annual maintenance cost, lined canal 


14. Annual saving in maintenance: (12) — (13) 

Labor Saved 

15. Labor, irrigating unlined canal:______ man-hours per year 

16. Labor, irrigating lined canal:_____ man-hours per year 

17. Annual saving in labor:_____ man-hours (15) — (16) at $_______per hour 


18. Total annual tangible benefits: (6) + (11) + (14) + (17) 
19. Estimated annual intangible benefits 
20. Total annual benefits: (18) + (19) 


$ 


PAPA w# 


13 


General Design Considerations 


canal location 


Irrigation canals should be so located that they 
serve as much irrigable land as possible. The ideal 
location would usually be one for which the cuts and 
fills would be balanced without excessive haul. In 
practice such a course is not rigidly followed since 
it would often result in many sharp curves. In un- 
lined canals sharp curves are objectionable because 
of the possibility of erosion damage; in lined canals 
they are undesirable because of the difficulty of 
operating slipform equipment around them. In 
locating canals to be lined, full advantage can be 
taken of steep grades to convey large flows at high 
velocities in relatively small canal sections. When- 
ever feasible, canals should be located along or ad- 
jacent to established property lines, existing roads or 
highways to avoid creating farm fields of irregular 
shape. 


size and shape of waterway 


Most irrigation canals, particularly those that 
are lined, have been built with flat bottoms and 
sloping sides. Such a section is reasonably efficient 
hydraulically and is also economical to build. Side 
slopes of 1!4 horizontal to 1 vertical are commonly 
used for concrete and soil-cement linings. Unpro- 
tected earth or rock slopes above the lining may be 
as steep as the nature of the material will permit. 
These are generally 1 to 1 or steeper for firm rock 
cuts, 14% to 1 for average earth cuts, and 2 to 1 or 
flatter for earth fills. 

For any specified volume of flow a number of 
different canal cross-sections, varying in bottom 


14 


width, depth and side slope, are possible. To take 
full advantage of the economy of using mechanized 
equipment in the construction of concrete linings 
for the smaller canals and laterals, cross-section de- 
signs with uniform side slopes have been proposed. 
These are shown in Fig. 1. Note that with only five 
different bottom widths, canal capacities of from 3 
to more than 700 cfs are made possible by varying 
the water depth and longitudinal slope. The benefits 
of such designs have been demonstrated most strik- 
ingly in the Gila Project in Arizona, where, over a 
period of three years and through 11 separate con- 
tracts, the average cost of concrete lateral lining has 
decreased slightly, though the national construction 
cost index has risen considerably. 

It should be noted, however, that occasions do 
arise when the equipment to which contractors have 
access cannot produce the exact shapes shown in 
Fig. 1. In the interest of economy, the use of this 
equipment should be carefully considered and should 
be permitted if it would produce linings with satis- 
factory hydraulic and structural properties. 

The normal freeboard required for a lined canal 
depends on its size and location, the possibility of 
storm-water inflow, and the degree of control that 
can be exercised over deliveries to and from the 
canal. Usually, 6 in. is considered to be the minimum 
desirable freeboard and should be adequate for con- 
crete-lined canals of capacities up to about 50 cfs. 
The freeboard should be increased to 1 ft. at about 
300 cfs and to 2 ft. at 2,500 cfs. In canals larger than 
farm-size laterals it is usually advisable to provide 
unlined banks above the top of the lining to help 


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FLOW IN CUBIG FEET PER SECOND 


Graph showing proposed cross-sections for lined canals with 2-, 3-, 4-, 5-, and 6-ft. base widths. 


Courtesy of Bureau of Reclamation. 


contain flash floods or unexpectedly large flows of 
irrigation water. These banks should range from 
1 ft. above the lining for capacities up to 50 cfs to 
1% ft. for 300 cfs. 


hydraulic computations 


There is no universally accepted method of 
cross-section design for open-channel flow; experi- 
ence and engineering judgment are depended upon 
to assure attainment of an adequate design. Several 
handbooks on hydraulics* are readily available and 
will be helpful to the engineer designing a canal sys- 
tem. The hydraulic design charts and tables in these 
and other handbooks are based on either the Chezy- 
Kutter or the Manning formula.** For most irriga- 
tion canal design problems these formulas give 
nearly identical results. In the application of either 
formula the coefficient of roughness (n) is usually 
taken as 0.014 for concrete linings, 0.015 to 0.018 
for shotcrete and soil-cement, and 0.025 for earth. 
“Hydraulic and Excavation Tables, U.S. Bureau of Reclama- 


tion, Denver, Colo. H. W. King, Handbook of Hydraulics, 
McGraw-Hill Book Co., New York. 


**See footnote on page 8 for the Manning formula. 


Lined canals should provide some freeboard above de- 
sign water surface. An unlined bank that extends some 
distance above the lining helps to confine the canal 
water if the lining is accidentally overtopped. Kittitas 
Main Canal, near Ellensburg, Wash. 


The velocity in unlined canals must be limited 
to that which will not cause cutting or erosion of the 
canal bottom or sides. This limiting velocity usually 
is 24% or 3% ft. per second, depending on the size of 
the canal and the character of the material. On the 
other hand, concrete linings have been used satis- 
factorily in canals with velocities as high as 15 ft. 
per second. When velocities exceed about 8 ft. per 
second care should be taken to make the wetted 
surface as smooth and free from abrupt changes of 
grade or direction as possible, since irregularities or 
obstructions might cause turbulence and consequent 
overtopping of the lining. Somewhat greater than 
normal freeboards (see above) also should be pro- 
vided, especially at turnouts and other structures. 


types of lining using 
portland cement 


As early as 1880 the use of portland cement 
mortar for lining irrigation canals came into favor. 
Since that time use of various types of linings made 
with portland cement has increased until these types 
now are generally recognized as possessing more 
desirable qualities than any other lining material 
of comparable cost. These linings vary in first cost, 
construction procedures or the materials used in 
combination with cement. This permits selection of 
the type that, at the lowest possible cost, will most 
nearly fit the conditions encountered. The following 
terms are used to describe the several types: 

Concrete is the term used for plastic concrete, 
either plain or reinforced, made with portland ce- 
ment, separated and processed aggregates and water. 

Pit-run concrete is plastic concrete made 
with portland cement and suitable unseparated 
pit-run sand and gravel of which not more than 12 
per cent will pass the No. 100 sieve. If less than 
15 per cent of the aggregate is retained on the \ -in. 
sieve the resultant concrete is usually referred to 
as “cement mortar.” 

Plastic soil-cement is a mixture of portland 
cement, soil and just enough water to produce a 
plastic consistency similar to that of masonry mor- 
tar; it requires no mechanical consolidation. 

Compacted soil-cement is a mechanically 
compacted mixture of portland cement and soil 
with optimum water content to give maximum 
density. 

Shotcrete is a pneumatically placed mortar 
made of portland cement, processed sand and water. 

Precast concrete is a term applied to con- 
crete units, usually interlocking, that are manufac- 
tured at a central plant and hauled to the job site. 

All of these linings have certain advantages 
that make them desirable for use in irrigation canals. 
Their long life, low maintenance requirements, struc- 
tural resistance to damage, and operating advan- 
tages make them particularly suitable as economical 
lining materials. 


16 


Canal Linings... Yez 


The Kittitas Main Canal, near Ellensburg, Wash., 
lined with concrete in 1926, has withstood satisfacto- 
rily the severe winter exposures in this area. 


Ridenbaugh Canal, near Boise, Idaho, lined in 1910 
with unreinforced pit-run concrete, is still in excellent 
condition after 45 years of service. 


Proven Service... Years of Service Ahead 


This section is typical of over 200 
miles of canals, lined with 114-in. 
shotcrete in 1940, in the Willacy 
County, Texas, Water Control and 
Improvement District No. 1. All of 
the shotcrete-lined canals are in ex- 
cellent condition and saving water 
every year. 


The plastic soil-cement lining was placed in this 
canal near Yuma, Ariz., in 1945. It is in good condi- 
tion and will serve for many more years. 


Gage Canal, near Loma Linda, Calif., was lined in 1886 with 
1 in. of cement mortar. Much of the original lining is still 
in good condition. 


factors affecting selection of type 


The most economical type of lining for a spe- 
cific project would be that which offers the greatest 
net annual saving, calculated as outlined on pages 
12—13, and which is also functionally suitable and 


The Coachella Canal in California, serving 80,000 acres 
of valuable, year-round farm land, must carry water 
continuously. The concrete lining ensures that opera- 
tion of the canal will not be interrupted by shutdowns 
for periodic maintenance or major repairs. 


satisfactory. Choice of the type would depend on a 
number of factors, among them: 

1. Size of canal and quantity of lining to be 
placed. Types of lining that require much equip- 
ment are not economical for small jobs. 

2. Importance of canal. Types that require the 
least maintenance are highly desirable for large 
canals where continuous operation is important. 

3. Availability of materials. In some localities, 
processed aggregates that are required for high-type 
linings may not be available within a reasonable 
haul, whereas unprocessed aggregates or suitable 
soils acceptable for lower types may be locally avail- 
able. The relative economy of the several types can 
be determined by comparing their annual costs as 
outlined in Form A, page 12. 

4. Climatic conditions. Higher quality linings 
usually will be more economical than lower types in 
regions where severe frost action occurs. Concrete 
with the greatest practicable resistance to freezing 
and thawing should be used in canals that have to 
be operated during the winter, such as power or 
reservoir supply canals. 

5. Grade and alignment. Types that are most 
resistant to abrasion should be used for canals with 
high velocities or frequent changes in direction. 

6. Other conditions. Lining an irrigation canal 
is justified if the annual benefits exceed the annual 
cost. However, the most economical type—the one 
that shows the greatest annual saving—may be the 
highest in first cost. If this first cost is beyond the 
financing ability of the water district or landowner, 
a lining with lower first cost is justified provided 
the annual benefits still exceed the annual cost. 


West Canal near Ephrata, Wash., carries irrigation water for 281,000 acres in the Columbia Basin Project. 


Courtesy of Bureau of Reclamation. 


Cast-in-Place Concrete Linings 


design 
thickness of lining 

No general rule can be stated for establishing 
the thickness of concrete linings. For small canals 
and ditches and in locations where frost action is 
not severe, unreinforced concrete linings 1% in. 
thick have been found adequate. Under similar cir- 
cumstances lightly reinforced shotcrete linings as 
thin as 1 in. have been used successfully. For larger 
canals, in cases where severe frost action occurs, 
where foundation or subgrade conditions are un- 
favorable, or where high velocities are inevitable, 
thicknesses of 2 to 444 in. have been used. 

Experience indicates that the minimum thick- 
ness for unreinforced concrete linings subject to 
average to severe conditions of exposure should be 
about 2 in. for canals up to 200 cfs capacity; 2% in. 
for canals of 200 to 500 cfs capacity; and 3 in. or 
more for larger capacity canals, depending on con- 
ditions of service and exposure. 


reinforcement and jointing 

The need for reinforcing steel in canal linings 
has been a much discussed and much misunderstood 
subject. The amount commonly used is so small that 
the steel does not add appreciably to the structural 
strength of an uncracked slab; in fact, additional 
structural strength can be obtained at less cost by 
increasing the thickness of the lining. 

Reinforcement will not keep the lining from 
cracking. Its main function is to hold together the 
edges of any crack that may form, thus reducing 
the width of the crack and preventing possible fault- 
ing of the cracked slab where unstable subgrade 
soils are encountered. 

If transverse joints are provided at such inter- 


vals as will reasonably control intermediate crack- 
ing, the use of reinforcing steel is of no material 
benefit and cannot be justified except under unusual 
conditions. 

If transverse joint spacing must be greater than 
that required to control cracking, or if unusual con- 
ditions are encountered, reinforcement,in proper 
amounts may be desirable. The amount of reinforce- 
ment required depends on slab length for longitudi- 
nal steel, and width for transverse steel. The neces- 
sary area of reinforcement can be found by the fol- 
lowing formula: 


in which 

A =the area in square inches of steel per foot of 
width in the direction in which L is meas- 
ured; 

L=distance in feet between free transverse 
joints in computing longitudinal steel or be- 
tween free longitudinal joints or edges in 
figuring transverse steel; 

f =coefficient of friction between slab and sub- 
grade (which varies from 0.5 to 3.0 depend- 
ing on subgrade material, a value of 1.5 to 
2.0 usually being assumed for average con- 
ditions) ; 

w = weight of the concrete slab in psf; 

s = allowable working stress in steel in psi (usu- 
ally assumed at about one-half the ultimate 
strength of the steel). 

It should be noted that the width of cracks at 
transverse joints in reinforced linings increases as the 
distance between joints increases. Therefore joint 
spacing should be limited to about 20 ft. to prevent 
large cracks, which make it difficult to keep joints 


19 


watertight. It is essential that reinforcement at 
transverse joints be stopped so that cracks will form 
at those points. 

joints 

Four kinds of joints are used in concrete canal 
linings. They are (1) construction joints, (2) trans- 
verse joints, (3) longitudinal joints and (4) expan- 
sion joints. 

A construction joint is placed at any location 
where it is expedient during construction. Usually 
it later performs the function of a contraction, longi- 
tudinal, or expansion joint. 

Transverse contraction joints are installed to 
control transverse cracking that results from shrink- 


This templet was used to form dummy groove con- 
traction joints in the concrete lining of the Columbia 
Basin Project in Washington. 


Transverse and longitudinal dummy groove contrac- 
tion joints in concrete-lined canal. Note the reinforced 
concrete structure for carrying surface runoff across 
the canal. 


age during volume change caused by drop in tem- 
perature or moisture loss. 

Spacing of transverse contraction joints to rea- 
sonably control cracking should be 8 to 15 ft., with 
the shorter intervals being used in thinner sections. 
Contraction joints are usually of the weakened- 
plane type formed by constructing a vertical groove 
in the top third of the concrete. This groove should 
be filled with a suitable sealing compound before 
the canal is placed in operation. 

Some small canals have been built of unrein- 
forced concrete without transverse joints. As would 
be expected, cracks form in these linings at intervals 
of 6 to 20 ft. If these cracks are properly maintained 
with an efficient seal they should not impair the 
efficiency or life of the lining. It is, however, more 
difficult to maintain random cracks than cracks that 
occur at carefully formed contraction joints. 

Longitudinal joints spaced 8 to 15 ft. apart are 
used to control irregular longitudinal cracking in un- 
reinforced slabs where the perimeter of the lining is 
greater than 15 ft. Such cracking is usually caused 
by contraction that results from drop in tempera- 
ture or by transverse warping of the slab due to 
temperature differential between the top and bot- 
tom of the slab. In reinforced slabs the amount of 
transverse steel usually used is sufficient to elimi- 
nate the need for longitudinal joints except in very 
large canals. In this case the amount of transverse 
steel required can be computed by the formula on 
page 19. 

Expansion joints in concrete canal linings ordi- 
narily are not required, except where the lining abuts 
fixed structures or under other extreme conditions. 
Experience has shown that the use of expansion 
joints has invariably resulted in increased openings 
of nearby contraction joints. This is undesirable in 
canal linings since it increases the difficulty of main- 
taining watertight joints. 

Expansion joints are used to prevent rupture 
of concrete due to excessive compressive stresses 
caused by an increase in moisture or temperature 
over that at time of placement. Research and ex- 
perience have shown that if compressive stresses can 
be kept within 50 per cent of the ultimate strength 
of the concrete, the possibility of failure is remote, 
and expansion joints are unnecessary. A slab that is 
fully restrained at both ends and subjected to a 100 
deg. F. increase in temperature over that at place- 
ment will develop about 1,500-psi compressive 
stress. This is 50 per cent of the ultimate compres- 
sive strength of most concrete used in canal linings. 
Furthermore, the shrinkage of concrete during hard- 
ening and the plastic flow under compression will 
tend to reduce the compressive stress resulting from 
expansion. 


subgrade considerations 


Ordinarily any soil that permits excessive seep- 
age is a Suitable subgrade material for concrete lin- 


ings. When unusually expansive subgrade materials 
are encountered, such as clay soils with excessive 
volume-change characteristics, construction meth- 
ods should provide for correction of the subgrade. 
Either clay can be pre-expanded by water-soaking 
prior to construction of the lining, or it can be re- 
moved and replaced with nonexpansive materials. 
In locations where impervious clay can trap water 
behind the concrete lining, provision must be made 
to relieve this hydrostatic pressure and thus prevent 
damage to the lining when the canal is empty. 

Occasionally, it may be necessary to construct 
a concrete-lined canal in an area where the ground- 
water is likely to rise above the bottom of the lining. 
In such cases it is necessary to provide drains under- 
neath or alongside the canal to relieve any hydro- 
static pressure that might cause uplift of the lining 
when the canal is empty. 

Special design and construction techniques usu- 
ally are required when the foundation material 
consists of large cobblestones, boulders or fractured 
or fragmented solid or semisolid rock. Overexcava- 
tion usually is necessary, since most specifications 
provide that no solid rock or boulders extend into 
the canal lining. The backfill or foundation material 
that fills the space between the bottom of the lining 
and the line of overexcavation should be carefully 
selected to ensure that it does not have undesirable 
volume-change characteristics and that it is of such 
gradation that the soil particles will not move into 
the coarser subgrade material. 


construction 


excavation and subgrade preparation 

For large canals, rough excavation usually is 
done with draglines, scrapers and other high-pro- 
duction earth-moving equipment. Final trimming is 
done with specially built machines, which operate 
on the same rails that will later support the slipform 
lining equipment. 


A concrete pipe subdrain was built to prevent hydro- 
static uplift on the bottom of the concrete-lined Fri- 
ant-Kern Canal in California. 

Courtesy of Bureau of Reclamation. 


Asubgrade-guided slipform was used 
for lining this canal in the Columbia 
Basin Project in Washington. Se- 
lected sand-gravel subbase placed 
over cobbly subgrade formed a 
stable, uniform base for the lining. 


Rail-mounted subgrade trimming 
machine prepares subgrade for con- 
crete lining of Friant-Kern Canal in 
California. 

Courtesy of Bureau of Reclamation. 


21 


One type of wing plow, tractor-pulled, that can be 
used to excavate and prepare subgrade for lining of 
small canals. 

Courtesy of Bureau of Reclamation. 


An embankment on which canal lining is to be placed 
should be thoroughly compacted by hand-tamping, 
rolling or water-soaking. Sheepsfoot or pneumatic- 
tire rolling, as illustrated here, is commonly used. 
Courtesy of Bureau of Reclamation. 


For smaller canals and farm ditches, excavating 
and trimming are often done with one machine. 
This may be a type of plow, which, in several passes, 
performs the necessary excavation and prepares the 
exposed surfaces for lining, or it may be a one-pass 
dredge or excavator. Where large quantities of lining 
are involved and where the subgrade soil is uniform 
and reasonably fine-grained, such machines do a 
remarkably economical job of excavating and trim- 
ming. 

Since most canal linings are installed to prevent 
seepage, the subgrade usually is quite free-draining. 
Sometimes, however, subgrade soils may be en- 
countered that have expansive characteristics re- 
quiring special moisture and density control prior 
to lining, as discussed under “‘Subgrade Considera- 
tions,’ page 20. This may involve placement and 
compaction of foundation soils at higher than nor- 
mal moisture contents. After preparation of the sub- 
grade, care should be taken to prevent any great 


22 


loss of moisture prior to placement of the lining. In 
all cases, just before the concrete is placed the sub- 
grade should be sprinkled in such a manner as not 
to form mud or puddles of water. 

Concrete lining should be placed only on fills 
or embankments that have been compacted by 
rolling, tamping, vibrating or water-soaking. On 
embankments where rollers, tampers or vibrating 
equipment is used, the material should be placed 
and compacted in approximately 6-in. layers at a 
predetermined optimum moisture content. 


quality concrete for canal linings 

Concrete used in canal linings should be so 
proportioned that it is plastic enough for thorough 
consolidation and stiff enough to stay in place on 
the side slopes. Since the concrete in canal lining 
does not act as a structural member, its strength 
usually is not an important factor. As a general rule, 
if the concrete is sufficiently durable to resist with- 
out damage the wetting and drying and freezing 
and thawing to which a canal is exposed, it will be 
strong enough for all but the most extreme condi- 
tions. Air-entrained concrete is recommended for all 
canal work and is particularly important where ex- 
posure to freezing temperatures is anticipated. Air- 
entrained concrete also is easier to handle and place 
than non-air-entrained concrete. 

Where soluble sulfates, such as sodium, mag- 
nesium or calcium sulfates, are present in the soil 
in appreciable quantities, either Type II or Type V 
cement should be used, the latter for extremely 
severe sulfate conditions.* 


mixing and placing concrete 

Concrete canal linings can be built by a variety 
of methods. Canals of considerable length usually 
are built with longitudinally operated lining equip- 
ment, commonly called slipforms. For large canals, 
with lining perimeters exceeding about 25 ft., slip- 
forms are supported on rails, a method that allows 
very close adherence to specified alignment and 
grade. For small canals, slipforms usually are sub- 
grade-guided, that is, the front portion of the slip- 
form rides directly on the previously prepared sub- 
grade while the rear portion serves as a screed, to 
distribute and smooth out the concrete. With this 
equipment the thickness of the lining is controlled 
within close limits; however, it is usual to permit a 
tolerance of 10 per cent reduction in specified lining 
thickness, provided that an average thickness is 
maintained, as determined by the volume of con- 
crete placed. With the use of subgrade-guided slip- 
forms alignment and grade of the finished lining 
depend almost entirely on the care and accuracy 
with which the subgrade is prepared; usually toler- 
ances of 2 to 4 in. in alignment and 1 in. in grade are 
considered reasonable. 


*Concrete Manual, U.S. Bureau of Reclamation (sixth 
edition), 1955, page 12. 


This view shows major steps in the 
construction of the Main Canal, Co- 
lumbia Basin Project, Washington. 
Equipment, reading from bottom of 
picture: subgrade trimmer, slipform 
liner, jumbo for cutting dummy 
groove contraction joints, jumbo for 
applying membrane curing com- 
pound. 

Courtesy of Bureau of Reclamation. 


On Arizona’s Gila Project, a subgrade-guided 
slipform was used to place the concrete lining. 
Courtesy of Bureau of Reclamation. 


The concrete lining of the Delta-Mendota Canal in California 
was placed with a rail-mounted slipform. 
Courtesy of Bureau of Reclamation. 


Where lengths of large canal are too short to 
warrant the expense of using slipforms, winch-drawn 
screeds operating transversely up each slope will 
usually be found economical. The lining ordinarily 
is built in alternate panels when this method is used. 
The construction joints between panels then func- 
tion as contraction or control joints. 

To produce a sound, fully consolidated slab of 
concrete with this method of placement, sufficient 
concrete must be available at all times to fill the 
space between the subgrade, forms and screed. 
Internal vibration of the concrete just ahead of the 
screed, at a frequency of at least 7,000 rpm, is 
preferable to having the vibrators mounted on the 
screed. A screed-mounted vibrator frequently causes 
the screed to jump, and, as a result, the concrete 
mass may not be vibrated properly. The surface then 


Slipform screed for placing concrete 
on the slope of a canal where the job 
is not large enough to warrant use of 
a longitudinally operated slipform. 
Pole Hill Canal in Colorado. 


Courtesy of Bureau of Reclamation. 


may be rough and the concrete poorly consolidated. 

Small canals and farm ditches often are lined 
by hand methods. Where low-cost labor is available 
or where farmers on a project can work coopera- 
tively on lining operations, hand methods frequently 
prove quite economical. 

Methods of mixing and handling concrete for 
lining irrigation canals are not greatly different from 
procedures used for paving streets and highways. 
For large canals, where large quantities of concrete 
are required, one or more dual-drum paving mixers 
can supply up to 200 cu.yd. of concrete per hour. 
For smaller canals one paving mixer is sufficient. 
Ready-mixed concrete is frequently used and is par- 
ticularly favored for reasons of economy where the 
concrete can be discharged from the truck directly 
into the slipform. 


Ready-mixed concrete is often used 
for canal linings, as shown here. 
Many miles of canals of this size have 
been built during the past 10 years. 


Continuous mixing of concrete or mortar is an- 
other method sometimes used for lining canals. The 
aggregate and cement are carefully proportioned in 
a windrow, the traveling mixing plant advances 
down the windrow picking up the material, water 
is added in the mixing chamber, and the mixed 
material is discharged via a chute or belt conveyor 
into the slipform. 

Small, mobile one- or two-sack, skip-loading 
mixers are recommended for projects where hand 
methods are used. 

Regardless of the mixing and handling methods 
used, it is important that the resultant concrete 
have adequate strength and durability for the con- 
ditions under which the canal will operate. Sepa- 
rated and processed aggregates generally are used 
for large jobs. Pit-run aggregates, which are at times 
used for smaller jobs or for jobs where processed 
aggregates are not readily available at a reasonable 
cost, should conform to the same standards of dura- 
bility and cleanliness as those established for proc- 
essed aggregates. Even though pit-run aggregates 
are well-graded, the proportions of fine to coarse 
aggregate ordinarily will not result in as economical 
use of cement as would be obtained with processed 
aggregates. Unless the saving in cost of aggregate 
exceeds the cost of the additional cement required, 
use of the pit-run aggregate is not justified. 

Regardless of the mixing and placing methods 
used and the source of aggregate, whether processed 
or pit-run, the water-cement ratio selected as suit- 
able for the conditions should not be increased. If 
more mixing water is needed for workability of the 
mix, the amount of cement should also be increased 
proportionately. 


curing concrete 
Proper curing is necessary to obtain the maxi- 
mum strength and durability of the concrete. Cur- 
ing also prevents rapid drying of the concrete, there- 
by reducing the possibility that shrinkage cracks 
will occur while the concrete is still plastic. Various 
methods and materials have been successfully used 


for curing concrete. Probably the material most 
often used for canal lining is liquid membrane seal- 
ing compound. Earth, straw, cotton mats, burlap or 
waterproof paper may be used for curing concrete. 
Any of these, with the exception of the waterproof 
paper, should be kept moist for the duration of the 
curing period, usually from 3 to 5 days. 


Slipform, operated with traveling pugmill mixing 
plant, was used to construct pit-run concrete lining 
on the Gila Project in Arizona. Other types of contin- 
uous mixers have been used to pick up windrowed ag- 
gregate and cement, mix them with the required 
amount of water, and discharge the mixture into the 
hopper of the slipform. The slipform for this job was 
pulled by a tractor. 


Courtesy of Bureau of Reclamation. 


Applying membrane curing com- 
pound to freshly placed concrete lin- 
ing. White-pigmented membrane is 
preferred because it will reflect the 
rays of the sun, thereby preventing 
excessive temperature rise during the 
day and corresponding drop at night. 
The membrane should be applied 
shortly after the concrete is placed. 


25 


Shotcrete Linings 


Shotcrete is a term that designates pneumat- 
ically applied portland cement mortar. Considera- 
ble mileages of both large and small irrigation canals 
and ditches were lined with 1- to 2% -in. thick shot- 
crete as early as 1917 and are still giving excellent 
service. Areas in which the use of shotcrete for canal 
lining predominates include the lower Rio Grande 
Valley of Texas (see photograph, page 17), where 
shotcrete linings have been built since 1929, and the 
Salt River Valley of Arizona, where irrigation dis- 
tricts have used shotcrete as a lining material for 
well over 20 years. Shotcrete linings also have been 
used successfully in the Yakima and Pasco areas, in 
the state of Washington; for the Gila Project, near 
Yuma, Ariz.; and by the Southern California Edison 
Co. in its power canals in the Sierra Nevada moun- 
tains of California. In these and other areas shot- 
crete continues in favor as a watertight, low-main- 
tenance material, both for lining existing canals and, 
occasionally, for resurfacing old lined canals. 

Because of the small amount of construction 
equipment required and its mobility, the shotcrete 
process is well suited to construction or repair work 
on small or widely scattered canal lining jobs, and 
also on farm ditches with frequent sharp curves, 
turnouts and other structures. Existing structures 
can be readily incorporated into the lining without 


26 


the building of complicated forms. Another advan- 
tage of shotcrete construction is that it can be placed 
on an irregular surface; therefore, some saving in 
subgrade preparation often can be made. However, 
while a shotcrete lining does not require as careful 
fine grading as a concrete lining does, no relaxation 
of quality standards for the subgrade, as discussed 
on page 20, should be permitted. 

Most of the advantages of shotcrete for lining 
irrigation canals stem from the somewhat special 
conditions outlined above. Since the rate of place- 
ment of shotcrete is very slow in comparison to slip- 
form concreting and since shotcrete is a mortar con- 
taining no coarse aggregate and hence requiring con- 
siderably more cement than is used in concrete, it 
almost always is more costly than slipform concrete. 
A further disadvantage of shotcrete is the difficulty 
sometimes encountered in controlling the thickness 
within the specified limits. Such control is particu- 
larly difficult if the subgrade is not trimmed to a 
reasonable degree of smoothness. Placement of shot- 
crete in two or more layers of 4% or % in. each, 
rather than in one thicker layer, will help produce 
linings that meet minimum thickness requirements. 
Use of a reinforcing mesh, placed in the center of 
the lining, also helps assure an adequate thickness 
in the placement of shotcrete lining. 


When the shotcrete lining was placed, in 1951, in the previously unlined Grand Canal, near Phoenix, 
Ariz., it was possible to reduce the size of the canal section considerably. 
Courtesy of Bureau of Reclamation. 


Concrete mixer for mixing sand and cement, and gun used to line canals 
near Yuma, Ariz., with shotcrete. With this equipment about 1,000 sq.yd. 
of 1-in. thick lining was placed each day. 


27 


Shotcrete, like concrete, expands and contracts 
with changes in temperature and moisture. A shot- 
crete lining built at a time of near maximum tem- 
perature for the locality usually will not require 
expansion joints. Contraction or shrinkage control 
joints, as discussed on page 20, are as desirable for 
shotcrete linings as for concrete. They probably 
should be deeper than for concrete, at least one- 
third to one-half the specified lining thickness. While 
shotcrete may be as strong as concrete and theoreti- 
cally capable of resisting high compressive stresses, 
the likelihood of thin spots and irregularities in 
alignment make a shotcrete lining less resistive to 
compressive forces than a concrete lining. Therefore, 
if a shotcrete lining is constructed during a period of 
much lower than normal temperature, some expan- 
sion joints to relieve compressive stresses due to 
future expansion are desirable. 

Sand for shotcrete should conform to the grad- 
ing requirement for concrete sand. Soft particles 
that crumble as they pass through the mixer, gun, 
discharge hose and nozzle should not be used, since 
they tend to break down into a powder, which 
would increase the water and cement requirement. 
The usual mix is 1 part of cement to 4 or 4% parts 
of sand, depending on climatic conditions, and a 
little less water than the amount that would cause 
sloughing. The 1:44 mixture has been satisfac- 


torily used in mild climates where freezing seldom 
occurs. 

The rebound when shotcrete is being placed 
usually has a greater percentage of coarse sand par- 
ticles and a much smaller cement content than the 
mortar leaving the nozzle. Therefore, the cement 
content of the mortar in place will be greater than 
that of the materials as mixed. 

Curing of shotcrete is as important as curing 
of concrete, and similar methods can be used. If a 
membrane sealing compound is used for curing, 
troweling into the surface the rebound that remains 
on the shotcrete may effect a saving in curing com- 
pound. Some improvement to the hydraulic proper- 
ties of the section may also result from lightly 
troweling the rebound, but this usually is economical 
only in relatively large canals. Troweling probably 
should be required only if its cost can be justified 
by the increased hydraulic capacity, but may be 
permitted at the option of the contractor, who may 
estimate that the cost of the troweling will be offset 
by the saving in membrane curing materials. Light 
troweling neither improves nor impairs the quality 
or strength of shotcrete lining.* 


* Additional information on shotcrete linings will be found in 
Shotcrete Canal and Ditch Linings, available free on request 
to the Portland Cement Association only in the United 
States and Canada. 


Shotcreting operations on Fort Sumner, N.M., Main Canal. After the shotcrete was 
placed, the rebound was troweled to effect a saving of membrane curing compound. 
A dummy groove contraction joint can be seen in the foreground. 

Courtesy of Bureau of Reclamation. 


In many areas native soils mixed with water 
and cement may be used to construct adequate 
canal linings of soil-cement. The suitability of the 
soil and the proportions of the mix to be used should 
be determined by laboratory tests.* 

Soil-cement linings are of two types, compacted 
and plastic. Compacted soil-cement is a relatively 
dry mixture of soil, cement and water, compacted to 
a high density. As the cement hydrates, a hardened 
lining results. Plastic soil-cement is a mixture to 
which sufficient moisture has been added to produce 
a consistency, at the time of placing, similar to that 


Compacting soil-cement in a small 
canal with vibratory equipment. This 
canal in the Columbia Basin Project 
in Washington was lined in 1954. 
Courtesy of Bureau of Reclamation. 


Soil-Cement Linings 


of masonry mortar. Both types have been used for 
lining irrigation canals and have been effective in 
reducing seepage losses and maintenance costs. 
Some linings of both types have been in service since 
1945 (see photograph, page 17), and based on their 
present condition, a service-life assumption of 20 
years is conservative. 


*Laboratory tests and construction procedures are outlined 
in Soil-Cement for Paving Slopes and Lining Ditches and Soil- 
Cement Laboratory Handbook, both available free on request 
to the Portland Cement Association only in the United 
States and Canada. 


Other Uses of Concrete in Irrigation 


precast concrete units 


Precast concrete slabs of sizes appropriate for 
handling by one or two men have been used to line 
canals. On small jobs or where small groups of un- 
skilled labor are available, precast concrete lining 
may have certain economic advantages over other 
types. However, either cast-in-place concrete or 
shotcrete generally will prove to be more economical 
for the average lining job.* 


concrete pipe 


Underground concrete pipelines have been used 
extensively for the transportation of irrigation water. 
Such pipelines have certain advantages over open 
concrete-lined canals. These advantages often are 
of sufficient economic importance to justify the 
use of concrete pipe. Since these pipelines are placed 
underground, cultivation can be carried on above 
the pipeline; no bridges or other crossings are needed; 
maintenance problems are minimized. Since con- 
crete pipe systems can operate under pressure, water 
can be delivered to land that could not be served 
by canals.** This is a major advantage in areas where 
scarcity of irrigation water is a problem. 

In some areas cast-in-place concrete pipe 24 to 
48 in. in diameter have been used for low-head irri- 
gation lines. In general, the cost of such installa- 


30 


tions has been higher than concrete-lined surface 
ditches of equal capacity. Equipment has been 
developed for constructing this type of pipe, with- 
out joints, in one operation. 


concrete tunnels, siphons 
and flumes 


Concrete is extensively used to line tunnels and 
to construct siphons and flumes for carrying canals 
over, under or through natural or manmade barriers 
such as streams, mountains, valleys, highways or 
railroads. Flumes usually are cast-in-place, but por- 
tions may be of precast concrete units. They may 
be rectangular, circular or of any desired shape that 
is appropriate or economical. Inverted siphons may 
be either cast-in-place concrete or precast concrete 
pipe. Precast pipe with an inside diameter as large 
as 15 ft. have been used. 


*A more complete discussion of precast concrete canal linings 
and suggestions for their manufacture and installation will 
be found in Precast Concrete Units for Ditch Linings, availa- 
ble free on request to the Portland Cement Association only 
in the United States and Canada. 


**A more complete discussion of this subject is contained 
in Irrigation with Concrete Pipe, available free on request to 
the Portland Cement Association only in the United States 
and Canada. 


A 48-in. unreinforced cast-in-place con- 
crete pipeline was constructed for irriga- 
tion of Orland Project, California, in 
1956. Pipe is formed with a subgrade- 
supported machine, which is pulled 
through the ditch. The part-circle alu- 
minum forms are left inside the com- 
pleted pipe until the concrete has 
hardened. 


Cast-in-place concrete was used for Dry Coulee Siphon No. 1, 
constructed in 1948 in the Columbia Basin Project, Washington. 
The siphon has 25-ft. inside diameter and 2-ft. thick walls. 


Courtesy of Bureau of Reclamation. 


Rectangular reinforced concrete flume carries Chandler Canal, Washington, on a ledge around a steep hill. 


Courtesy of Bureau of Reclamation. 


miscellaneous structures 


In the construction of checks, drops, turnouts, 
division boxes, measuring devices—such as weirs and 
Parshall flumes—and other canal structures, the use 
of cast-in-place concrete and shotcrete has been 
extensive. In some localities precast concrete units 
have been found to be more economical, easily in- 
stalled and entirely satisfactory.* 

Bridges across irrigation canals must be 
provided at intervals. Concrete, because of its many 
advantages, is a desirable material for such canal 
crossings. In recent years precast and prestressed 
bridge members, which can be mass-produced in 
central plants and easily erected at the site, have 
come into favor. 

Reinforced concrete is the preferred construc- 
tion material for larger structures in irrigation proj- 
ects or canal systems. Concrete is particularly desir- 
able for powerhouses and pumping plants, where 
its long life, low maintenance requirements and fire- 
proof characteristics combine to produce a structure 
that has low annual cost. 


*Suggested designs and details are contained in Concrete 
Irrigation Structures for Farm Ditches and Low-Cost Irriga- 
tion Structures, available free on request to the Portland 
Cement Association only in the United States and Canada. 


Printed in U.S.A. C1-2 


32 


Construction of 72-in. concrete irri- 
gation pipeline on a distribution 


compacted by jetting and vibrating. 
Courtesy of Bureau of Reclamation. 


Parshall flume for measuring flows in shotcrete-lined 
canal near Burbank, Wash. 
Courtesy of Bureau of Reclamation. 


system in California’s Central Valley — 
Project. Backfill around the pipe was — 


Architectural concrete power plant near Estes Park, Colo. Durable, firesafe, economical concrete is the preferred 
construction material for major power and pumping plants. 


Courtesy of Bureau of Reclamation. 


Bibliography 


“Canals and Related Structures,”’ 
Design Standard No. 3 of Rec- 
lamation Manual, Bureau of 
Reclamation, U.S. Department 
of the Interior, Washington, 
D.C., April 1952. 


Fortier, Ernest C.,‘‘New Machine 
Casts Continuous 48-In. Diam- 
eter Concrete Pipe in Place,” 
Western Construction, Septem- 
ber 1955, pages 44—45. 


“Laboratory Tests on Canal Lin- 
ings,” Pacific Builder and En- 
gineer, July 1952, pages 62-63. 


Linings for Irrigation Canals, Bu- 
reau of Reclamation, U.S. De- 
partment of the Interior, 
Denver, Colo., July 1952. 


McCauley, Gulley, ‘““The Econ- 
omy of Canal Linings,” [rriga- 
tion, Engineering and Mainte- 
nance, June 1952, pages 9-12. 


Nutley, Van E., ‘“Try-Outs for 
Precast Canal Linings,’’ The 
Reclamation Era, November 
1947, page 234. 


Reeves, A. B., ‘“‘Linings for Irri- 
gation Canals,’ Proceedings, 
National Reclamation Associa- 
tion, Washington, D.C., 1954, 
pages 40-60. 


Robinson, William J., and Tuthill, 
Lewis H., “‘Better Concrete in 
Slope Paving by Use of Slip- 
Forms,” Journal of the American 
Concrete Institute, September 
1955, pages 1-11. 


Rohwer, Carl, and Stout, Oscar 
Van Pelt, ‘““Seepage Losses from 


Irrigation Channels,” Technical 
Bulletin 38, Colorado A. & M. 


College, Fort Collins, 
March 1948. 


Wilkinson, Garford, ‘‘Fort Sum- 
ner’s Concrete Laterals,’’ The 
Reclamation Era, September 
1952, pages 208-209, 212. 


Womack, Donald E., “‘Gunite Lin- 
ing to Stop Seepage,’ Western 
Construction, May 1952, pages 
59-60. 


Woodford, T. V. D., “‘Slip-Forms 
for Concrete Canal Lining,” 
Proceedings of the American 
Concrete Institute, Vol. XLVIII, 
1952, pages 637-644. 


Colo: 


CONCRETE 


SEWERS 


CONCRETE SEWERS 


CHAPTER | History of Sewers . Page 1 
INTRODUCTION Use of Concrete in Sewers Page 1 
Economy . Page 5 
CHAPTER 2 Adaptability . Page 5 
ADVANTAGES OF CONCRETE Strength . Page 5 
FOR SEWER CONSTRUCTION WAS Ula Posed 
Durability Page 5 
CHAPTER 3 
Flow in Sewers . Page 8 
HYDRAULICS OF SEWERS 
CHAPTER 4 Selection of Type of System Page 11 
TYPES OF SEWER SYSTEMS Sewer Lines Defined Page 11 
CHAPTER 5 Preliminary Investigation Page 12 
Sanitary Sewers F Page 13 
DESIGN OF SEWER SYSTEM Storm or Combined Sewers . Page 17 
CHAPTER 6 Loads Caused by Backfill Page 22 
LOADS ON SEWERS Surface Loads . . Page 30 
Excavation Page 33 
CHAPTER 7 Pipe Sewers. . . . Page 35 
Jacking Concrete Pipe Page 40 
CONSTRUCTION Subaqueous Sewers Page 41 
Cast-in-Place Sewers . Page 41 
CHAPTER 8 Manholes eee ah ar Page 42 
Lampholes, Inlets, Catch Basins and Flush Tanks Page 43 
SEWER APPURTENANCES Pumping Stations, Siphons, and Chambers _ . Page 45 
CHAPTER 9 Cause of Failures and Repair Methods Page 46 
Sewer Appurtenances Page 47 
MAINTENANCE AND REPAIR Safety Precautions Page 47 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, techn 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold prog! 
of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engages 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on requ 


CHAPTER | 


INTRODUCTION 


History of Sewers 


E LIVE IN AN AGE of concrete and steel, chro- 

mium and plastic—an age of push-button control. 
When we think of days gone by, no doubt, we feel our 
ancestors knew little of the refinements common to our 
modern way of life. Nevertheless, men of ancient times 
provided their cities with running water and sewers for 
drainage. 


Early Sewers 


Explorations reveal that they understood drainage principles 
and applied them to the construction of sewers and drains. 

For example, in an excavation at Nippur, India, a sewer 
arch constructed about 3750 B.C. was unearthed. Another 
excavation in Tell Asmar, near Bagdad, revealed a sewer 
constructed in 2600 B.C. The Minoans, who lived on the 
Island of Crete about 1700 B.C., were master builders and 
installed elaborate systems of well-built stone drains which 
carried sewage, roof water and general drainage. In Rome, 
the famous large drain called the Cloaca Maxima was con- 
structed about 200 B.C. and was in service until the begin- 
ning of this century. 

With the exception of the drains built by the Minoans, 
however, these drains were not constructed so that sewage 
was directly discharged into them since dwellings did not 
have the water carriage system of waste disposal. Waste 
which accumulated in the street gutters eventually was 
flushed into the sewers but their main purpose was the 
removal of storm water. In spite of the early use of sewers 
little progress was made during the middle ages in the 
removal of storm drainage and sanitary wastes. The latter 
were deposited in the gutter. 


Modern Sewers 


Sewer construction in Europe was speeded during the latter 
part of the nineteenth century by terrible outbreaks of 
Asiatic cholera. In London the construction of sewers con- 
centrated the wastes of millions of people in the Thames 
River. The monstrous odor nuisance which resulted was one 
of the main topics of the time, even disrupting meetings of 
parliament. Sewers were being constructed in the United 
States during this period but many of our major cities did 
not have extensive systems until 1915, and even today all 


of our cities need additional sewer facilities. Although it is 
evident that sewer construction is not a new art, only during 
recent years has there been any widespread construction of 
sewers for both storm drainage and sanitary wastes. It is 
also evident that many more are needed. 


Use of Concrete in Sewers 


Concrete has been used in sewer construction for many years. 
The Romans used concrete in much of their construction 
including sewers. The large sewers constructed in Paris dur- 
ing the middle of the 19th century were built of rough 
stone heavily plastered with cement on the interior. Dr. 
Rudolph Hering, a well-known sanitary engineer, reported 
in 1915* that his examination of the interior surfaces of 
these sewers showed them to be quite good. He attributed 
this to the “density and the smoothness of the plaster”. In 
1881 he also examined concrete sewers in Vienna and found 
no disintegration although they had been constructed 10 
to 20 years previously. 


Concrete Pipe 


Concrete pipe have been used successfully for sewers in the 
United States for many years. A partial list of communities 
reporting the early use of concrete pipe is shown in Table 1. 
Many towns in the New England states installed “cement 
pipe” during the last quarter of the 19th century and some 
of these are still being used. In Chelsea, Mass., concrete pipe 
were installed in 1869 and are functioning satisfactorily 
today. Springfield, Mass. first used concrete pipe in 1882 and 
prefers their use in sewers larger than ten inches in diameter 
because of their economy and durability. 

Concrete pipe were installed in a combined sewer in 
St. Paul, Minn., in 1873. St. Paul has 35 miles of this type 
of pipe sewers in sizes from 21 to 72 in., all of which have 
given fine service. 

In San Antonio, Texas, almost 250 miles of concrete 
pipe from 6 in. to 90 in. in diameter are in use in sanitary 
and storm sewers. 

From 1925 to 1930 concrete pipe were used in Miami, 
Fla. for the extension of its sewerage system. A critical sur- 
vey of these pipe was made in 1947, with special attention 


*Concrete Cement Age (July 1915), page 31. 


COPYRIGHT 1958 BY PORTLAND CEMENT ASSOCIATION 


Left—A section of 20-year-old 8-in. concrete pipe removed from Miami, Fla. sanitary sewer system in 1947 for inspection and study. Note excellent 
condition of pipe as is evidenced by the uniform thickness of wall and sharp markings on outside of pipe. Right—This 12-in. concrete pipe was in- 
stalled in a combined sewer on Washington St. in South Bend, Ind., in 1889. It was removed in 1937 and now serves as an outdoor flowerpot. 


to points where unusual conditions might be expected. The 
results of this survey indicate that the concrete pipe have 
given good service. 

In presentday practice portland cement concrete pipe 
are proving their strength, durability and economy in all 
sizes from 6-in. house connections to mammoth 12-ft. diam- 
eter outfall sewers. The uniform dimensions and shape of 
concrete pipe assure good alignment and watertight joints. 
Their smooth interior facilitates flow and decreases the 
amount of fall required for self-cleaning velocity thereby 
reducing excavation costs. 


Cast-In-Place 


Large cast-in-place concrete sewers were not constructed in 
the United States until the last quarter of the nineteenth 
century. A partial list of communities reporting the early 
use of cast-in-place concrete sewers is shown in Table 2. 
Their use was stimulated by the construction in 1873 of a 
15 x 17.5-ft. concrete sewer in Washington, D.C., by D. E. 
McComb, superintendent of sewers. This was so successful 
that it encouraged the construction of large cast-in-place 
sewers in other cities. Since then concrete has been used in 
the construction of the majority of the large sewers built 
in this country. For example: 


Minneapolis,Minn. has 80 miles of 36-in. to 11-ft.cast-in-place 
concrete sewers. 
Boston, Mass. has had extensive experience with cast-in- 
place concrete sewers since the installation 
of a concrete combined sewer in 1904. 
Kansas City, Mo.does not consider any other material for 
the construction of large sewers. Since 
1905, this city has built about 220 miles 
of cast-in-place concrete sewers varying 
from a 30-in. horseshoe section to twin 
17 x 18-ft. rectangular sewer. 
Saginaw, Mich. first installed cast-in-place concrete sewers 
in 1905. It has 12 miles of this type, the 
largest being 6 ft. 8 in. x 16 ft. 


PAGE 2 


Atlanta, Ga. has 112 miles of combined concrete sewers 
constructed from 48-in. diameter to twin 
9 x 13-ft. sections. Its first installation has 
been giving good service since 1910. 


The Sanitary District of Chicago has more than 200 
miles of large concrete intercepting and outfall sewers in 
use. In 1948 this district completed 71,000 lin.ft. of concrete 
sewer sections in tunnel, ranging in size from 16 ft. 6 in. x 
8 ft. 4 in. to 18 x 20 ft. 

Concrete is particularly well suited for either small or 
large sewers. It can be designed for any load and for any de- 
sired shape. Its excellent service record together with its 
many advantages accounts for its wide and growing use in 
sewer construction. 


Construction of 18 x 20-ft. concrete section of the south side in- 
tercepting sewer by the Sanitary District of Chicago in 1946. 
Tunnel was mined to full section and supported by steel ribs and 
liner plates. Inside steel forms in sections 5 ft. long were moved 
into place by the traveler shown in foreground. Concrete was 
then pumped and vibrated between the liner plates and these 
inside forms. Photo courtesy Sanitary District of Chicago. 


TABLE | 


Partial List of Cities Where Early Installations of Concrete PIPE SEWERS Were Made 


— - “ ee 


DATE FIRST CONCRETE SYSTEMS IN USE 
CITY USED TYPES REMARKS 


No trouble. 
Still functioning well. Liked by 
city officials. 


Salem, Mass. 1860 Separate and storm 
Chelsea, Mass. 1869 Separate 


Milwaukee, Wis. 1871 Separate, storm and Some early concrete pipe built 
combined in 1871 still in use. 
Burlington, Vt. 1871 Separate Satisfactory service. Considered 


more economical in larger sizes. 


St. Paul, Minn. 1873 Combined Has proven very satisfactory. 
Portland, Maine 1873 Separate and storm Good. 
Greenfield, Mass. 1880 Combined Satisfactory. Better structurally in 


larger sizes. 

Satisfied with concrete. 
Durability preferred over other 
materials. 


Passaic, N.J. 1880 Separate and storm 
Springfield, Mass. 1882 Separate and combined 


Southbridge, Mass. 1899 Separate and storm In good condition. 
Greeley, Colo. 1900 Separate Still in excellent condition. 
St. Petersburg, Fla. 1903 Separate and storm Estimated life of pipe about 


50 years. 
Dover, N.H. 1903 Combined Excellent. 
Adams, Mass. 1903 Storm Estimates life as indefinite. 
Lansing, Mich. 1903 Separate Excellent. 
Kearny, N.J. 1905 Separate and storm Long life, O.K. 
Saginaw, Mich. 1905 Combined Good. 
Enid, Okla. 1906 Separate and storm Very good. 
Monrovia, Calif. 1906 Separate Excellent. 
Newark, N.J. 1909 Combined Satisfactory service at low cost. 
1922 Separate 
Salt Lake City, Utah 1909 Sanitary and storm No failures of record. 
Yakima, Wash. 1909 Separate Satisfactory. 
Bellingham, Wash. 1910 Separate and storm Have given satisfactory service. 
Key West, Fla. 1912 Separate and storm Very good service. 
Kansas City, Mo. 1912 Separate and combined Considered the equal of competi- 


tive materials. 


San Antonio, Texas 1917 Separate and storm Excellent. 

Pekin, Ill. 1920 Separate and combined Satisfactory. 

Hoquiam, Wash. 1922 Storm and combined Satisfactory. 

Atlanta, Ga. 1923 Separate Entirely satisfactory. 
Little Rock, Ark. 1923 Separate Very good. 

Beaumont, Texas 1923 Separate and combined Excellent. 

Houston, Texas 1923 Separate Good. 

Bluefield, W.Va. 1923 Separate Satisfactory. 

Evanston, Ill. 1924 Combined Satisfactory. 

Jacksonville, Fla. 1924 Separate Satisfactory. 

Springfield, Ill. 1925 Separate Satisfactory. 

Winona, Minn. 1925 Separate Satisfactory. 

Jackson, Miss. 1926 Separate Completely satisfactory. 
Richmond, Va. 1926 Separate and combined Completely satisfactory. Concrete 


used exclusively. 
Satisfactory. 


Montebello, Calif. 1928 Separate 


PAGE 3 


TABLE 2 


Partial List of Cities Where Early Installations of Concrete CAST-IN-PLACE Sewers Were Made 


DATE FIRST 


CONCRETE SYSTEMS IN USE 


CITY 


Rochester, N.Y. 


USED 


TYPES 


Storm and combined 


REMARKS 


Still in operation. 
No maintenance. 


Washington, D.C. 1873 Separate, storm and Excellent life. More economical 

combined than precast pipe. 

Minneapolis, Minn. 1881 Separate, storm and Still in good condition. No re- 

combined placements or trouble. 

Salt Lake City, Utah 1892 Sanitary and storm No failures of record. 

Niagara Falls, N.Y. 1896 Combined Still operating. No maintenance. 
Appear to be standing up in 
good shape. 

Batavia, N.Y. 1898 Storm Excellent. No maintenance. 

Pittsburgh, Pa. 1900 Separate and storm A few failures due to loads not 
anticipated. 

Hannibal, Mo. 1900 Storm Good. 

Springfield, Mo. 1900 Storm Excellent service when properly 
designed and constructed. 

Memphis, Tenn. 1900 Storm Good. 

Trenton, N.J. 1900 Storm Satisfactory. 

Columbus, Chio 1900 Separate, storm and Records show no failures. 

combined 

Swampscott, Mass. 1903 Separate and storm O.K. 

Jacksonville, Fla. 1903 Storm Satisfactory. 

Oklahoma City, Okla. 1903 Storm and combined No complaints. Apparently in ex- 
cellent condition today in spite 
of handling considerable oil 
field wastes. 

New Orleans, La. 1904 Separate and storm Cast-in-place storm sewers 
entirely satisfactory, some 
having been in service 44 years. 
Economy entirely satisfactory. 

Saginaw, Mich. 1905 Combined Good. 

Kansas City, Mo. 1905 Separate, storm and Good. No trouble. Only thing 

combined considered for large sizes. 

Peru, Ind. 1905 Storm Satisfactory. 

Clinton, lowa 1905 Separate, storm and No failure, no trouble. 

combined 

Ironton, Ohio 1905 Storm and combined All in excellent shape. More 
economical to build. 

Mattoon, Ill. 1905 Combined Is in good condition. 

Winchester, Mass. 1905 Storm No trouble to date. 

Alexandria, Va. 1905 Storm and combined No failures or other adverse 
experience. Concrete used almost 
exclusively. 

Waterbury, Conn. 1905 Separate Some wear at certain points, 
otherwise, durable. Economy 
favorable. 

St. Paul, Minn. 1905 Combined Still in satisfactory working order. 

Milwaukee, Wis. 1905 Storm and combined All in service to date. 

Alhambra, Calif. 1905 Storm Excellent. 

Dallas, Texas 1907 Separate and storm Still good. 

Louisville, Ky. 1908 Combined Good. 

Bellingham, Wash. 1909 Separate, storm and O.K. 

combined 

Atlanta, Ga. 1910 Combined First installation giving satisfac- 
tory service. 

Phoenix, Ariz. 1914 Storm Good. 


PAGE 4 


CHAPTER 2 


ADVANTAGES OF CONCRETE 
FOR SEWER CONSTRUCTION 


HE WIDE acceptance of concrete for sewer construc- 
tion can be attributed to its: 


1. Economy 

2. Adaptability 
3. Strength 

4. Watertightness 


5. Durability 


Economy 


Concrete for sewer construction is economical because it 
can be made with local labor at or near the site with ma- 
terials which are produced locally or within a reasonable 
haul. Loss from breakage is reduced to a minimum. 

Concrete can be molded and finished to a true, even 
surface. This results in economy in size of the sewer, for ca- 
pacity increases as the frictional resistance to flow decreases. 
Its long life and low maintenance costs mean low annual 
cost, the true measure of economy of any construction ma- 
terial. 


Adaptability 


Cast-in-place concrete can be designed and built to fit any 
desired shape of sewer section. Thus economy in design can 
be obtained without sacrifice of structural strength or stabil- 
ity. For example, local conditions may permit the use of a 
high arch section which has a greater structural capacity and 
is more economical than a circular or flat arch. It is also 
possible to provide a design which will maintain desirable 
hydraulic characteristics such as self-cleaning velocity for 
varying depths of flow. Special shapes also may be designed 
for economical use when obstructions or right-of-way widths 
are encountered which would interfere with the construction 
of the normal cross section. 


Strength 


Reinforced concrete can be designed to meet the conditions 
of any depth of backfill and superimposed loads. It is one 
material in which strength increases with age. ASTM specifi- 
cations for concrete pipe provide for several classes of pipe 
to meet different conditions of load. Today, with the use of 
processed and graded aggregates, proper proportioning and 
control, adequate curing and modern equipment, mixed-in- 
place concrete or concrete pipe can be made to attain the 
quality and strength required. 


Watertightness 


A prerequisite for the efficient and satisfactory sewer is 
watertightness. Infiltration of storm or underground water 
causes overloading of the sewer system. This additional 
water interferes with, and adds to the cost of, the normal 
operation of the sewage treatment plant. The migration of 
soil particles into the sewer by infiltration through cracks 
and joints will cause settlement of sewer lines and streets 
and result in costly repairs. In properly designed and con- 
structed cast-in-place sewers, there is little likelihood of any 
abnormal amount of infiltration. In the presence of moisture, 
minute cracks in concrete pipe or cast-in-place sewers will 
seal themselves through autogenous healing. Tests indicate 
that after such sealing the strength of the concrete is not 
impaired. 

Cement mortar joints in concrete pipe lines can be made 
reasonably watertight by grouting, caulking or by pneumatic 
placement. Rubber gaskets backed up with cement mortar 
have been very effective in preventing infiltration. For a 
more complete discussion of the various types of joints and 
jointing materials see page 38. 


Durability 


A durable material is one which will satisfactorily resist 
service conditions to which it will be subjected. In sewers 
this means resistance to: (1) weathering; (2) possible 


PAGE 5 


ne 


Two concrete pipe removed February 1951 for inspection after 23 years 
of use by the Sanitary Sewer District in Pine Bluff, Ark. It is apparent 
from the excellent condition of these pipe that they are still good for 
many more years of service. 


chemical action and (3) wear. Concrete has proved its 
durability under these conditions as is evidenced by the 
satisfactory record of performance of precast pipe and cast- 
in-place sewers in almost every section of the country. 


WEATHERING. The quality of well-made concrete to re- 
sist the action of freezing, thawing, wetting, drying and 
temperature variations is well known. Since sewers are for 
the most part constructed underground, weathering action 
is minimized and the durability of concrete in sewers under 
these conditions of exposure is unquestionable. 


CHEMICAL ACTION. Sewage is the used water supply of 
a community, consequently the nature of sewage is influ- 
enced to a large extent by the chemical composition of the 
water supply. Public water supplies are normally alkaline 
and so domestic and industrial wastes, except from a few 
manufacturing or commercial establishments, are generally 
alkaline. 

Strong acid wastes are highly corrosive to sewer struc- 
tures and equipment. Excessive acidity or alkalinity is also 
harmful to the sewage treatment processes. The Federa- 
tion of Sewage Works Associations in its Manual of Practice 
No. 3, “Municipal Sewer Ordinances” recommends a per- 
missible range of a pH 5.5 to pH 9.0 for sewer systems. If 
this regulatory provision is adopted and enforced there is 
little, if any, danger of any corrosion of concrete sewers. 

Acid conditions which would cause corrosion usually 
are limited to branch lines which carry the sewage from the 
offending establishment to the main or lateral sewer. From 
that point on the acidity of the sewage normally is neutral- 
ized by dilution with larger volumes of domestic sewage, 
high in alkalinity. 


PAGE 6 


There are relatively few locations where acid or alkali 
soils will be encountered in sewer construction that are likely 


| 


to cause deterioration of concrete. Research and experience — 


have indicated that portland cement concrete mixtures can 
be designed to resist the corrosive action of sewage or soils 
having a pH as low as 5.5 and alkali soils high in sulfate 
(10 per cent soluble salt content) .* 

To be resistant to acids having a pH as low as 5.5, 
concrete should be composed of sound aggregates, plus a 
well-designed rich mix (w/c not > 5 gal. per sack.) to pro- 
duce an impervious concrete. Methods of placement which 
will eliminate segregation and honeycomb, together with 
adequate curing are essential requirements. The use of air- 
entraining portland cement or an air-entraining agent adds 
certain desirable characteristics to the concrete, such as in- 
creased workability, reduced segregation and bleeding. 

To be resistant to the corrosive action of alkali soils 
high in sulfates, the concrete should be made of portland 
cements of types that are sulfate resisting (ASTM or Federal 
types II or V), in addition to the requirements outlined in 
the preceding paragraph. 

When the pH of the sewage or a soil is less than 5.5 or 
the concrete is in contact with alkali soils extremely high in 
sulfates the concrete should be given a protective coating as 
outlined in the Portland Cement Association information 
sheet, Effect of Various Substances on Concrete and Protec- 
tive Treatments Where Required**. 


HYDROGEN SULFIDE. Failures of sewer structures 
caused by oxidation of hydrogen sulfide gas have been so 
widely publicized that many engineers believe they are a 
general rather than an infrequent occurrence. Actually, fail- 
ures have occurred in relatively few localities and even then 
only in certain portions of the sewer system where condi- 
tions prevailed which contribute to hydrogen sulfide genera- 
tion. 

Hydrogen sulfide gas is undesirable in any sewer system. 
This gas has a highly offensive and objectionable odor which 
emanates from manholes and permeates entire neighbor- 
hoods; it corrodes paints, metals and other materials. 

As a consequence, steps should be taken to prevent the 
generation of this gas. 


*Dalton G. Miller and Philip W. Manson, “Durability of Concrete 
and Mortars in Acid Soils with Particular Reference to Drain Tile”, 
Technical Bulletin No. 180, University of Minnesota, Agricultural 
Experiment Station. 

“Long-Time Study of Cement Performance in Concrete” Bulletin 30 
Chapter 5, Portland Cement Association Research Laboratories. 
Special Publication of the American Concrete Institute, Detroit, 
Mich. 

Thomas E. Stanton, “Durability of Concrete Exposed to Sea Water 
and Alkali Soils, California Especially”, ACI Journal, Vol. 19, No. 9 
(May 1948), page 821. 


** Available free from the Portland Cement Association. Distributed 
only in U.S. and Canada. 


Temperature, strength, velocity of flow, age of sewage 
and ventilation are the principal factors affecting the genera- 
tion of hydrogen sulfide. In most communities the time 
the sewage remains in the system is not long enough to cause 
septic action. Therefore, age of sewage is not a contributing 
factor except possibly in our largest cities. Even in these 
instances it has been found that the concentration of sulfide 
was less in the lower reaches than anticipated because of the 
natural purification which takes place in long sewer lines. 

In spite of the fact that concrete is used almost univer- 
sally for large-sized sewers there have been some instances 
where its use has been restricted in the smaller-sized sewers. 
Since the smaller sizes are almost invariably in the upper 
reaches of the sewer system where sewage is fresh and largely 
composed of domestic wastes, there is apparently no justi- 
fication for such restriction. 

Pomeroy and Bowlus* in extensive tests conducted in 
the vicinity of Los Angeles found that with gravity flow, “for 
any particular temperature and sewage strength combination, 
there is a limiting flow velocity above which sulfide build-up 
will not occur.” They suggest combining the strength of 
the sewage as determined by the Biochemical Oxygen De- 
mand** (BOD) and the temperature of sewage into a single 
term known as “Effective Biochemical Oxygen Demand” by 
the formula: 


Effective BOD=Standard BOD**x(1.07)*?°, where 
t=temperature of sewage in degrees centigrade. 


Available data indicate that minimum velocities re- 
quired to prevent sulfide buildup for various values of effec- 
tive BOD are as follows: 


Minimum velocity 


Effective BOD (feet per second) 


55 1.0 
125 iS 
225 2.0 
350 P26) 
500 3.0 
690 3.5 
900 4.0 


The minimum velocity for various values of effective BOD 
is shown graphically in Fig. 4 on page 15. 

When the temperature of the sewage is below approx- 
imately 20 deg. centigrade (68 deg. E) no appreciable sulfide 
buildup will occur. Since the temperature of the water for 
industrial and domestic use is usually below 68 deg. E, the 
used water in a sewer system with few exceptions should 


*Richard Pomeroy and Fred D. Bowlus, “Progress Report on Sul- 
fide Control Research”, Sewage Works Journal, Vol. 18 No. 4, 
page 597. 


**Standard Methods for Examination of Water and Sewage, 8th 
Edition, 1936, published by American Public Health Association. 


not exceed 68 deg. E These exceptions would be hot wastes 
from certain establishments or areas where extremely hot 
weather prevails for long periods of time. 

The conditions favorable to the generation of hydrogen 
sulfide are largely the combinations of high temperature and 
strength of sewage with low velocities. Where it is imprac- 
tical to provide a sewer gradient that will give the required 
limiting velocities, other means of controlling sulfide genera- 
tion should be considered. Reduction of effective BOD can 
be accomplished by diluting the sewage with water thereby 
reducing its strength and temperature. Proper ventilation 
is helpful in reducing sulfide concentrations by removing 
sewer gases and by inducing aerobic conditions. This may 
be accomplished through house stacks, perforated manhole 
covers, specially constructed shafts and unobstructed outlets. 
Chemicals can be used to control or eliminate sulfide genera- 
tion by sterilizing the sewage or suppressing biological 
activity. Chlorine has been used the longest for this purpose. 
Recent studies also have shown that nitrates and shock treat- 
ments with lime are effective in many situations. Periodic 
cleaning and flushing of sewers are essential to the efficient 
operation of a sewer system and have frequently reduced 
sulfides to negligible concentrations where they formerly 
were a problem. 

With proper design, construction and maintenance the 
possibility that hydrogen sulfide generation and buildup in 
sewer systems will damage the concrete is extremely remote.* 
This is substantiated by the excellent performance of con- 
crete and concrete pipe sewers during the past 50 years. 


WEAR. In the American Concrete Pipe Association publica- 
tion, Concrete Pipe Lines it is reported that concrete pipe 
12 in. to 63 in. in diameter on grades up to 22 per cent in 
Los Angeles and vicinity show only slight abrasion during 
14 years of service. In San Diego, storm sewers on slopes up 
to 45 deg. show only slight wear after 22 years of service. 
At Duluth, Minn. 12-in. concrete pipe storm sewers on grades 
up to 26 per cent showed but slight abrasion. Actual per- 
formance records are substantiated by tests** which indicate 
concrete will resist the erosion of clean water at extremely 
high velocities if there is no abrupt change in direction or 
velocity of flow to cause turbulence. These tests indicate 
that the resistance of concrete to abrasion increases as its 
strength and density increase. 


*A more complete discussion of the subject may be found in 
Effect and Control of Hydrogen Sulfide in Concrete Sewers, a Port- 
land Cement Association publication, available free on request. 
Distributed only in U.S. and Canada. 


** Arthur V. Davis, “Safe Velocities of Water on Concrete”, Engi- 
neering News-Record (January 4, 1912), page 20. 
Lewis Tuthill and R. F. Blanks, “Erosion of Concrete by Cavitation 
and Solids”, ACI Journal (May 1947), page 1009. 


PAGE 7 


CHAPTER 3 


HYDRAULICS OF SEWERS 


N COMPUTING the hydraulic capacity of sewers it will 
be assumed that sewage has the same flow characteristics 

as water. This is substantially correct as the small per cent of 
solids normally present does not materially affect the flow. 


Flow in Sewers 


Sewage, like water, seeks its own level. Flow by gravity 
through a sewer, therefore, may be induced by a difference 
in elevation, known as “slope” or “grade”. Flow also may be 
induced by pressure either by pumping or surcharging. Nor- 
mally, sewers flow only partially full and are not under pres- 
sure. The flow, therefore, is similar to that in open channels, 
such as streams and canals, and formulas based on open- 
channel flow are used in sewer design. It is assumed that the 
volume of flow past successive cross sections of the sewer 
conduit will be uniform in area, shape and velocity. This is 
known as “uniform flow” and only prevails in a conduit in 
which the volume of sewage, slope, size and alignment of the 
sewer do not change. Since appreciable changes generally 
occur only at manholes, uniform flow is assumed to exist be- 
tween manholes and the hydraulic gradient of the sewer is 
assumed to be parallel to the invert of the sewer. When the 
velocity of flow is known the capacity of a sewer can be 
computed from the expression Q=aV, when Q=quantity 
of flow in cubic feet per second; a=cross-sectional area of 
conduit in square feet; V=velocity of flow in feet per second. 


Velocity of Flow 


For determining the velocity of flow many formulas have 
been devised. 

The Chezy formula for velocity, V=C\WRS, was de- 
veloped in 1775 and has been the basis of most of the more 
recent formulas for velocity in open-channel flow. In this 


PAGE 8 


formula C is a coefficient, R is the hydraulic radius 

area of cross-section 
( wetted perimeter 
in feet per foot. 


)and S is the slope of sewer expressed 


In 1869, Ganguillet and Kutter made a study of open- 
channel flow experiments and developed an expression for 
C. This substitute for C in the Chezy formula is commonly 
known as the Kutter formula which has been used widely 
even though it is rather complicated. This value for C is ex- 


pressed as: 
41.65 + 9200281 4 1.811 
C= 
1+ Fa(41.65+ —¢F 
Where x=coefficient of roughness. 
486 


The Manning formula, ya R*S™” has also been 


used for open-channel flow. It gives results closely approxi- 
mating Kutter’s formula and because it is simpler it is pre- 
ferred by some engineers. 

The value of » is approximately the same in both the 
Kutter and Manning formulas. Its value depends upon the 
roughness of the material of which the sewer is constructed. 
It also varies slightly with depth of flow, being greater for 
low flow than for conduits flowing full. The values of x for 
concrete vary from 0.010 to 0.015. If concrete sewers are 
carefully constructed, it is reasonable to assume 7 as 0.012. 
The calculations in this publication are based on this value of 
n for all depths of flow. 

The above formulas apply to sewers of all shapes flow- 
ing either full or partially full. A diagram, Fig. 1 (see next 
page) has been prepared for the solution of Kutter’s formula 
for concrete circular sewers flowing full. 

Fig. 2 has been prepared for use in determining the 
hydraulic properties of circular sewers at various depths of 


ic Feet Per SECOND 


UB 


U 


Stope IN FEET PER THOUSAND FEET For Kutter Formula, n=0.012 

7060 50 40 30 2 10.918 18 GN 543 2 109080706 05 04 03 2 Ol a 
Se DA anna GE Pa US ©. GSA 4 PA Wa aN Da Da WA PAN EA Zs RSENS NEN NN Wa Ne] 

SSCS SR OS a is 


ANAT AN 


x XO 
EX : moe TOSI RCL WADARS SEAS SSAS, 

ZA OOF 6 OVA DASE ANTAL ps aD: NN PAK IN oO \Oxes NN! 
CE OOOS CANON ADEE CECA NORe ue 
C66 GOSSAGE Ww SOI ZAIN 


LOR SAV Se OANe 6 SUM os rN x SLX WN POXS ano = eG 
SSO ORS POCA SIS EASOLACTSBh hoc \ De Ue 


BOK NA, EEE eran > Pd eal ZANDT EAT EA WAT ARS 4 TOS i 
AK SECAECAROREalbe SES BAR LOPS PSX DTN Sc yn 
Vg s } IX SSE eo 
KNX XX SAX ANN OX aw oy ae 
400 OND CNC 00 CC UaGP GEE OF OOr LO (AUP CUR AU Re TOA. 2 ® id 
EX IOAN XT ROMO AE PRR CIDA DT NSPS SATAN]? 
: SORA DR PQA SPOS A 
WB PRE IRE SSS RSI 
az DOSER het MS IONE ne 
ening Wx E 
f eee: FA, AY } BAAS x a GYAN AS WX a 
OOOO OE NNOANNI IST ON AlN Gt OrgO htza CaN OOS 
9 SZ oe GANA ISS Za Urethra NNGNines 
GEO EEW 
ZSERIES SSRI 


2 eeeeeeeeaeaet 


iN 


I 
iN 
IND 
WK 


- 


A 


ZZ tH is ooze A 5 
weeceeeees eee 
fe seceecexs = Pere 
suseazaceee. (eee acamesaneazeacet 
Hucweeece cee ieeeeeeeel 
Peper et oe a peceececcesl 
siteeccacc ecco cs ritceseseeac 
ecetsepae aesaaee aegaes 
acecucaeae srcer anes 
as20708 = , LECCE EA 
iaiutiagee eee ca aartaitl 
urate eum as) ate 8 ate 2 on zi = : 
deutebecceme soca centers 


Copaiiccececcegce, 


Vetocity IN Feet Per SECOND 
FIGURE !—Flow Diagram for Concrete Pipe Sewers 


: : as ax NO NK xf Cy 
( ANAS OSA ONO OE SONOS Seal 
ZS RSS| ESNAINE SAA eee! . 


NT 


A 
INE 
eS 


YY 
SONNE 
SKN 
N AANNE 
TNNA 


Shy 
NON 
\\ \ 

YAN 
NS 


ANS 
“NANG 
sb 


NN 
\N 
a 
ik 
IN} 
Nh 
eh 
NK 
ai 


NN 
Me 
Ni H 

S. 
ANNAN. 
iN 


N 


ae 
AAR 
ASN 
KIN NAN 


NING 
XT NIN 
NUE 


NSH 


N) 


N 


LIN 
val 
M 


as 


IN 


BS 
eoERs 
SoCs 
KYW 
SSS 


am 
KEN 
Sas 


\ 


.— 
TIME OF FLOW IN MINUTES 


ToD 


7 


\s 


aw 
SSN 
Ssh 


<1 


ro) 
Ne) 
o 
w 
nN 
° 
ut 


PAGE 9 


1.00 


{SX 


.80 


10 


-©0 


-50 


40 


Relative depth of flow 


30 


.c0 


.60 


1.30 


1.20 


.80 1.00 1.10 


Hydraulic elements in terms of hudraulic elements for full section 


NE 
V full’ 


Q 


Qfun *Afun 24 


A R 
R full 


FIGURE 2—Hydraulic Elements of Circular Sections 


flow for »=.012. For other values of and for other than 
circular sections similar graphs can be prepared by deter- 
mining the hydraulic radius for each depth of flow and sub- 
stituting this R in either Kutter’s or Manning’s formula. 


Minor Frictional Losses 


In addition to the frictional loss considered in the Kutter 
and Manning formulas there will be head losses in the sewer 
caused by bends, manholes, junctions, increases in sewer size 


PAGE 10 


and change in the slope. These losses are minor when com- 
pared to frictional loss in a long line and ordinarily are not 
considered in sewer design. Some designers arbitrarily allow 
a few hundreths of a foot loss of head at each manhole. 

Wherever changes in sewer sizes are necessary the crown 
of the smaller incoming sewer should be above the invert 
of the larger outgoing sewer by an amount ot Jess than 
eight-tenths the diameter of the larger sewer. Unless this is 
done the smaller sewer will be surcharged when the larger 
sewer is flowing at maximum capacity. 


CHAPTER 4 


TYPES OF SEWER SYSTEMS 


EWER SYSTEMS are classified according to the type of 
service they render: (1) storm sewers; (2) sanitary 
sewers and (3) combined sewers. 
STORM SEWERS, also called storm drains, carry storm 
and surface waters, street wash and other wash waters or 
drainage, but exclude sewage and industrial wastes. 


SANITARY SEWERS, also called separate sewers, carry 
sewage into which storm, surface and ground waters are not 
intentionally admitted. Although the primary purpose of 
sanitary sewers is the transportation of sewage, a certain 
amount of storm and ground waters find their way into the 
system. 


COMBINED SEWERS, are those designed to carry both 


storm water runoff and sewage in the same conduit. 


Selection of Type of System 


The type of sewer system most desirable for any community 
is dependent upon a number of factors. A combined sewer 
is preferred in many instances because of its economy. It 
requires the construction of only one line which need be 
little, if any, larger than that required for storm water runoff. 
Thus the cost of an additional line for sewage flow is saved. 
In a combined sewer, flushing automatically occurs during 
periods of heavy rainfall. This keeps the sewer line clean 
and reduces maintenance costs. A combined sewer is also 
less costly to the individual property owner as only one con- 
nection from the house to the sewer is required. 
In spite of these advantages, certain factors may warrant 
the construction of separate systems. Among these are: 
(1) topography 
(2) soil conditions 
(3) operation of sewage treatment plant 
(4) character of sewage 
(5) existing improvements 
Topography of the area has an important bearing on 
size of sewer, depth of excavation, pumping requirements 
and the location of sewage treatment plant. Topography may 
permit the discharge of storm water at locations where it 
might be objectionable to discharge sewage, even though 
diluted. Should pumping be required, the added cost of 
pumping combined sewage may warrant the use of a sep- 
arate system. 
Since sanitary and combined sewers are normally re- 
quired to be deeper than storm water sewers, any excava- 


tion difficulties such as rock, quicksand, muck, etc. encoun- 
tered in the construction of a larger combined sewer might 
be more costly and make a separate system more desirable. 

Combined sewers usually are designed so that only the 
normal dry weather flow reaches the sewage treatment plant. 
Nevertheless, excessive quantities of diluted sewage may 
reach the plant during periods of heavy rainfall and interfere 
with the normal operation and efficiency of the sewage treat- 
ment plant. 

The character of the sewage may make separate systems 
desirable. For example, if expensive coatings or linings are 
required to protect the sewer against corrosion it would be 
cheaper to protect a smaller sanitary sewer than a larger 
combined sewer. 

Existing improvements abutting the sewer as well as 
existing street and sewer improvements may be important 
factors to be considered. These and other factors affecting the 
relative cost of combined or separate sewers must be care- 
fully studied before the one best suited to community needs 
can be determined. 


Sewer Lines Defined 


The various branches of a sewer system are defined: 
HOUSE SEWER. A pipe conveying sewage from a single 
building to a common sewer or point of immediate disposal. 
LATERAL SEWER. A sewer which discharges into a 
branch or other sewer and has no other common sewer tribu- 
tary to it. 

BRANCH SEWER. A sewer which receives sewage from 
a relatively small area and discharges into a main sewer. 


SUBMAIN SEWER. An arbitrary term used for relatively 
large branch sewers. 

MAIN SEWERS. A sewer to which one or more branch 
sewers are tributary. Also called trunk sewer. 


INTERCEPTING SEWER. A sewer which receives dry- 
weather flow from a number of transverse sewers or outlets 
and frequently additional predetermined quantities of storm 
water (if from a combined system), and conducts such waters 
to a point for treatment or disposal. 

RELIEF SEWER. A sewer built to carry flows in excess of 
the capacity of an existing sewer. 

OUTFALL SEWER. A sewer which receives sewage from 
a collecting system and carries it to point of final discharge. 


PAGE II 


CHAPTER 5 


DESIGN OF SEWER SYSTEM 


ANITARY, storm and combined sewers are defined in 

Chapter 4. Because of the difference in volume and 
character of the wastes which they transport, the design of 
a sanitary sewer is quite different from that of a storm water 
sewer. The design for combined sewers is generally the 
same as that for storm sewers, since the volume of sewage 
is so small in comparison with storm runoff that as a rule 
it need not be considered. 


Preliminary Investigation 


Before a satisfactory plan for a sewer project can be developed 
the engineer must collect and analyze certain data pertaining 
to the project obtained through surveys of the area which 
the project will serve. Topographic and underground features, 
data concerning population, information on domestic sewage 
and industrial wastes, and weather statistics must be ob- 
tained. 


Topography Survey 


An accurate topographic map of the area is essential to the 
design of a sewer system. This map should show the location 
of all buildings as well as all road, block and street lines. 
Industries and institutions such as engraving, metal pickling 
works and hospitals which discharge wastes of unusual 
character should be carefully noted. The location of possible 
sewer obstructions, stream crossings and the type and thick- 
ness of pavement on all streets is also necessary. The map 
should show the depth of basements, particularly if a sani- 
tary or combined sewer is under consideration. 


Subsurface Survey 


Underground conditions along the route of the sewer should 
be investigated to determine the character of the soil, the 
depths to the ground water levels and the location of all un- 
derground obstructions. Representative soil borings should 
be taken at frequent intervals along the proposed route. A 
study of these soil samples will help the design engineer to 
decide where support beneath the sewer is necessary, where 
bracing and sheeting of the sewer trench will be required, 
where water-bearing soils and rock may be encountered. Such 
information also will be valuable to the contractor during 
construction. 


PAGE 12 


It is important to locate all underground utilities which 
may influence the placing of the sewer, such as existing 
sewers, drains, water mains, gas mains, telephone and light 
cables, conduits and buried gasoline tanks. To avoid pollution 
of existing wells it is also important to know their exact loca- 
tion, so that the sewer lines will not be placed or constructed 
in such a manner as to endanger these sources of potable 
water supply. 


Estimate of Future Population 


Population is an important factor to be considered in the 
design of separate sewers. From census records which show 
the past growth of the community and from a general knowl- 
edge of the area, population growth may be forecast. In ad- 
dition, a forecast as to the probable distribution of population 
and industry is necessary to determine the size of laterals and 
mains for sanitary sewers. 


Waste Survey 


The quantity of domestic sewage to be expected will depend 
largely upon the water consumption of the community. Since 
most of the water used will be discharged directly or indi- 
rectly into the sewer, flow in the sanitary sewer will approxi- 
mate the amount of water consumed. This amount will vary 
with the character and the geographical location of the area. 
Residents in higher income brackets use more water pet 
capita than those in lower brackets. In some areas the use of 
water-cooled air conditioners adds to the volume of sewage 
flow. The records of water consumption both private and 
public and the character of all wastes within the limits of the 
sewer system should be determined in the preliminary in- 
vestigation. 


Weather Information 


In the design of storm and combined sewer systems, the 
volume of storm water runoff is important. The intensity, 
duration and prevailing direction of rain storms, the slope 
and condition of the surface of the area in question affect 
the surface runoff. The U.S. Weather Bureau has many sta- 
tions scattered throughout the country where weather infor- 
mation and data can be obtained. Intensity and duration of 
rainfall data are far safer and more reliable if drawn from a 
study of the occurrence at several stations in the area than if 
drawn from only one station. 


Eight-inch concrete pipe sanitary sewer construction in Oak Park Sub- 
division, Lake Charles, La. by First Sewerage District, in 1949. 


Sanitary Sewers 


The main function of a sanitary sewer is to carry maximum 
sewage flow which will occur during the period for which 
the sewer is designed and to carry that flow at such veloci- 
ties that suspended solids will not be deposited in the sewer. 

The period for which a sewer is planned is based on its 
economic life. This may vary in different parts of the system. 
For example, it is more practical to construct a relief sewer 
for an overloaded main sewer than it is to build parallel lines 
for the branch and lateral sewers because of the greater 
mileage of the latter. For this reason the branch and lateral 
sewers usually are designed for 50 years or more while the 
main sewers may be based on a shorter period. 


Quantity of Flow 


Quantity of sewage will vary in different sections of a city. 
In residential districts governing factors are the area, the 
density of population per acre, water consumption and the 
amount of ground water infiltration. Commercial districts 
as a rule produce a higher flow than residential sections but 
are usually smaller in area. The flow from manufacturing 
areas depends largely upon the type of industries in the area. 

The density of population per acre will vary with the 


Density of Impervious 


Character of population surface 
district Development per acre percentage 
Dense residential § 2-family houses and 55 34 
6-family apartment 
buildings 
Medium residential Mostly single family a2 27, 
houses 
Light residential Single family houses 15 20 
only, some on double 
lots 
Mercantile 14 100 
Light commercial 30 80 
Industrial 10 60 


character of the district. Hansen* gives population densities 
for 50-ft.-width lots with average conditions (below, left). 
RESIDENTIAL DISTRICTS. As indicated in the section 
on preliminary investigations, sanitary sewage flow from a 
residential neighborhood approximates the water consump- 
tion of that area. If the area is not metered, the design must 
be based on the expected flow as determined from the eco- 
nomic status and habits of the people, character of the area 
and other factors influencing water consumption. Gaging of 
the flow in sewered areas will assist in determining the 
Capacity required. Long-time gagings are the most reliable 
but shorter periods, carefully evaluated, may be helpful. 
Since sewers must carry the peak flow, the daily and hourly 
variations in the use of water should be investigated. These 
will vary in different communities as well as different sec- 
tions. In most areas a higher maximum flow can be expected 
on Mondays. Fig. 3 presents a typical curve showing varia- 
tions on an average day. Keefer** gives a table listing 32 
cities in which the average flow in separate sewers varied 
from 41 to 282 gal. per capita daily with an average for the 
32 cities of 104 gal. per capita. For smaller communities the 
average daily flow is probably less than 100 gal. per capita, 
particularly for residential communities. 

Since there is more variation in the flow from sparsely 
populated residential areas, the tendency is to assume a 
higher ratio of maximum to average flow for small cities. 


Babbitt* * * has proposed the formula M= for estimating 


the ratio of the maximum to the average flow in residential 
areas. In this formula, M is the ratio of the maximum to the 
average flow and p is the population of the area 7m thousands. 
It is recommended that M should not be less than 1.50 and 
should not exceed 5.0 which means that for populations of 
less than 1000 the maximum rate of flow would be five times 
the average rate, and for populations greater than 400,000 
the maximum would be 1.5 times the average. 

INDUSTRIAL DISTRICTS. As it has been stated the 
volume of industrial waste to be expected will depend upon 


*Paul Hansen, “The Relation of Zoning to the Design of Drainage 


and Sewerage Systems.” ASCE Transactions, Vol. 88, page 680. 
**C. D. Keefer, Sewage Treatment Works, First Edition, page 18. 


***H_E. Babbitt, Sewage and Sewage Treatment, Sixth Edition, page 
Be 


60 
% sol 
* aol 
fe) 30/4 
® 20 
ro tol 
Sorry ial 
€ 90}— 
%S 80 
@ 70 
ba en a 
% tots 
e Zo oS ee aia 
ete 6 12 6 12 
| am pm | 
Hour of day 


FIGURE 3—Hypothetical Daily Average of Water Flow 


PAGE 13 


the type of industry which is tributary to the sewer. The 
engineer’s knowledge of the types of wastes produced will 
be helpful in determining whether they must be entirely 
excluded from the sewer, whether they must be treated be- 
fore being discharged or whether the sewer structure must 
receive some protective treatment. 


INFILTRATION. Infiltration should be kept to a mini- 
mum in sanitary sewers since it reduces the carrying capacity 
of the sewer, increases pumping costs and overloads treat- 
ment units. Infiltration occurs through: (1) improperly con- 
structed joints in the sewer and mortar joints in masonry 
manholes; (2) openings in manhole covers; (3) poorly con- 
structed basements and house drains. The following pre- 
ventive measures will minimize infiltration: 


a. Careful joint construction with competent, continuous 
inspection. This requirement also applies to the con- 
struction of house connections. 

b. Proper bedding of pipe sewers to avoid settlement or 
breakage. 

c. Construction of watertight manholes. This is important 
as manholes and catchbasins, unless properly built, 
are likely to be one of the main sources of infiltration. 
Cast-in-place or precast concrete construction is ad- 
mirably suited for this purpose since there are few 
joints through which water may enter. 

d. Prohibiting the connection of roof downspouts and 
foundation drains to sanitary sewers. 

Surveys of existing sewer systems in service for some years 
have shown rates of infiltration extending over a wide range 
from 1500 gal. to more than 100,000 gal. per mile of sewer 
per day. For average conditions, where ground water is en- 
countered above the sewer line it is reasonable to assume 
for design, infiltration of about 60,000 gal. per mile of sewer 
per day, or about 1500 gal. per acre per day. 

The infiltration allowance specified in construction 
should be less than that used in design. By good jointing 
procedures and strict supervision during construction the 
amount of infiltration into the sewer proper should be kept 
at about 1500 gal. per day per inch of diameter per mile of 
sewer. Poor joint construction of house drains later may in- 


crease the total infiltration per mile. 


Velocity of Flow 


Sanitary sewers are normally designed on a basis of a mini- 
mum velocity of 2 fps flowing full to prevent the deposi- 
tion of organic solids. Experience has indicated that these 
sewers will be self-cleaning at such velocities if the sewer 
flows more than half full. The design should be checked to 
determine whether there will be sections in which velocities 
below self-cleaning will prevail at minimum flow for ex- 
tended periods of time.* Such sections may require the in- 
stallation of flush tanks or an increase in the slope of the 
sewers to keep them clean. Concrete sewers can be designed 
for rather high velocities provided turbulence can be mini- 
mized. Abrupt increases in velocity because of steep slopes 


*Thomas R. Camp, “Design of Sewers to Facilitate Flow’, Sewage 
Works Journal, Vol. 18, No. 1 (Jan. 1946), page 9. 


PAGE |4 


or sudden changes in direction of flow should be avoided to 
minimize abrasion where velocities exceed 8 to 10 fps. 


Control of Hydrogen Sulfide Generation 


VELOCITY. With proper design, hydrogen sulfide genera- 
tion and evolution can be controlled to prevent any damage 
to the sewer structure. One of the most important factors in 
preventing the formation of this gas is the velocity of flow. 
The limiting velocities vary with temperature and strength 
of sewage (effective BOD). See Fig. 4. The velocities shown 
on page 7 are suggested as the minimum that should be used. 
If industrial or hospital wastes are present carrying large 
amounts of organic matter, velocities greater than the mini- 
mum may be desirable. 


FORCE MAINS. Lack of aeration in long force mains 
causes sulfide buildup. Where force mains are necessary, con- 
sideration should be given to the design of gravity flow 
sewers with vertical lift pumping stations, rather than the use 
of long force mains. 


TURBULENCE. Drop manholes or improperly designed 
junction manholes or any other feature of design which may 
cause turbulence in the flow may lead to excessive release of 
hydrogen sulfide. Therefore, these conditions should be care- 
fully avoided in design. 


OTHER METHODS. If it is impractical to obtain the 
recommended velocities to prevent sulfide buildup, other 
means of controlling sulfide generation should be considered. 
Among these are ventilation of the sewers, aeration of the 
sewage, use of chemicals to inhibit biological action and the 
control of “the effective BOD” by dilution with water. 


PROTECTIVE LINERS AND COATINGS. Protective 
liners should be used only where it is impractical to control 
the generation of hydrogen sulfide. Protective coatings 
should be considered as supplemental protection rather than 


a substitute for proper design or construction. In any case 


high quality concrete is a primary requisite for durable long- 
lasting sewers. 


Typical Example 


The following illustrates the method of determining the size 
of sanitary sewers required for the area shown in Fig. 5. 


ASSUMPTIONS 


(1) Population of the community or area to be sewered, 
1600; 


(2) Density of population, 40 persons per acre; 
(3) Average rate of flow, 100 gal. per capita per day; 


(4) Maximum rate of flow 5 times the average or 500 gal. 
per capita per day; 

(5) Minimum size of circular concrete sewer, 8 in.; 

(6) Maximum rate of infiltration, 1500 gal. per acre per 
day; 

(7) Minimum velocity in sewer flowing full, 2 fps; 


(8) Value of the coefficient of roughness n=0.012 for 
use in Kutter’s or Manning’s formula; 


(9) Minimum depth to invert of sewer, 6 ft.; 
(10) Loss of head through each manhole, 0.08 ft. 


Effective B.O.D. (PPM) 


(a 000; 0 


S 
a 


Velocity required (FPS) 


eh ree) 3.0 


BS 


Si CoS 


BaD WES 


WNSOS= ie 
Fy Lome Os | ere (Ss | Gt [ea | ea |e [es | ig ee] en ee eee eae a SS 


SNS Se 


CM 


Or 
DSS e 


i 
Wy 
y 
/ 
ig 
Vii 
| 
fz 
fel 


200 300 400 500 


Standard B.O.D. (5- ae 20°C), (PPM) 
EXAMPLE: For standard B.O.D. of 200 and temperature of sewage of 75° F., the effective 
B.O.D. is 260 and the required velocity to prevent sulfide buildup is 2.2 feet per second. 
NOTE: From “Progress Report on Sulfide Control Research”, by Richard Pomeroy and 
Fred D. Bowlus in SEWAGE WORKS JOURNAL, Vol. 18, No. 4, July 1946, pp. 597-640. 


FIGURE 4 — Velocity Required in Sewer to Prevent Sulfide Buildup 


PAGE I5 


Future ar 


Future ra 
(15 Acres) (1S Acres) 


=| a 


__ Metcalf Street 


i: ‘lf 
alg HU i UU 
iii ie Ui 5 Ac HAP EH JOE 
Base: 


uf siata | an eae 
° 
it i a | 


hat 


ee 


Street 


Street 


PROFILE 


FIGURE 5—Plan for Sanitary Sewer Example 


SOLUTION. Lay out the sewer as shown in Fig. 5. Man- 
holes are located and numbered along the line of the sewer 
at intersections of streets, junctions with lateral sewers and 
at intermediate intervals of about 300 ft. A table similar to 
Table 3 will be found useful in tabulating the design compu- 
tations. Starting on line 1, enter data for columns 1, 2 and 3. 
In column 4 is entered the contributary area between man- 
hole No. 6 and manhole No. 5 which totals 2.5 acres. Since 
this is the beginning of the sewer, enter 2.5 acres also in 
column 5. Columns 6, 7, 8, 9, 10 and 11 are self-explanatory. 
Column 12 may be computed from Kutter’s or Manning’s 
formula or may be obtained directly from the flow diagram 
for circular sewers, shown in Fig. 1, page 9. In this figure 
the flow in cubic feet per second is shown on the left-hand 
side of the chart and is represented by diagonal lines running 
upward to the right. The slope in feet per thousand is shown 


PAGE 16 


at the top of the figure and is represented by lines running 
diagonally downward to the right. The velocity in feet per 
second is shown at the bottom of the figure and is represented 
by approximately vertical lines. The diameter of the sewers 
is shown on the right-hand side of the figure and is repre- 
sented by approximately horizontal lines running to the left. 
Thus, if any two values are known, the other two on the 
chart can be determined. 

For a total flow of .08 cfs (column 11) and a minimum 
velocity of 2 fps, it is seen from this flow diagram that the 
size of the sewer will be less than the 8-in. minimum as- 
sumed. For an 8-in. sewer flowing full at a velocity of 2 fps 
it is seen that a slope of 3.5 ft. per thousand will be required 
with a resulting capacity of .70 cfs. The velocity of the 
actual total flow of .08 cfs in the 8-in. sewer can be deter- 
mined from Fig. 2, page 10, as follows: 


a COMPUTATION SHEET FOR HYDRAULIC PROPERTIES OF SANITARY SEWER 


SEWER LOCATION SANITARY SEWAGE 


hyo teed 


SEWER DESIGN 
(From Fig. 1) 


ION (mgd)| TOTAL FLOW 


SEWER PROFILE 


Additional, _. 
Pibviory a Tributary <S a ai Upper end Lower end 
population D ~- 2 
janee oe 8 E | a = 
| 5 ref) (ea Pe ce 
l= sj ol, jo = = = = 
| i) 3 E3\s | ae eerie) etal Eg = = 
| | é 5 |sen(eis|/# |e ie me Srp apa 
| — a— | Le] am - 
Name of Street a —_, ee 28 x 2 =) £ 2/5 ° = ees < 
z} | — 9° 8| 5 z) | 3 - o & _ 3 > ° -_ = 3 | = o 
|2£\ 2 mall = Ke iS 28 =v |/avix|s | 8 ° ry dies tx) ee s > = > 
ne dg 6 | —Ex(8 Selo lpcmade sea ierateece ecu hon an 
ike 3 | 8x | NI PEeclolten Sieeur ra lieic| ecg so. 2) joni ee 
Waal Es A eS Se ee Rea eo 2a coe PSE leae 8) tcl eue 
Siro Woe Omir ;Cten oo S.0 SS lsolai ete peer(s els | -s js} sie 
[joie | < |e |S) ee | EN £2) OC ~ (col nel Ome | > nev Ot wo oO 
| | | | | | | 
(1) (2) (3) (4) >) (5) 5/566) eZ een (10) (11) (12) (13)) (14) | (15) | (16) | (17) (18) (19), (20) (21) 
lley between Metcalf andEddy 6 5] 2.5) 2.5 100 | 100 | .050 0.05375 | 0.0833| 8 3.5 0.70 2.0] 1.3 | 330 68.00 6.0 66.85 7.0 
lley between Metcalf andEddy 5 4 2.5| 5.0| 100 | 200 .100 0.10750/0.1663| 8 3.5 0.70 2.0] 1.5 | 330 66.77 7.1 65.61 8.4 
lley between Metcalf and Eddy | 4|3]17.5 | 22.5 700 | 900, .450 0.48375 0.7484| 10 3.5 1.4 2.4| 2.4 | 330 65.44 8.6 64.29 9.5 
| | | | | 
lley between Metcalf andEddy 3 2] 2.5/ 25.0 100 | 1000, .500 0375 0.5375 |0.8315| 10 | 3.5| 1.4 | 2.4 | 2.5 | 330 | 64.21 | 9.6 | 63.05 | 7.0 
lerring Street | 2| 1115.0 | 40.0 600 | 1600 .800 060 0.8600 | 1.3304] 10 (9.42.4 3.9] 4.0 | 165 62.97 7.1 61.42 6.0 


;\d=Million gallons per day. 


The ratio of actual flow to the capacity of the 8-in. 

sewer is Q _.08 
Ofulled0 os 
Enter Fig. 2 from the bottom at 

.11 thence vertically upward to the discharge curve, thence 
horizontally to the right to the velocity curve, thence verti- 
cally downward to the bottom of the figure where the value 

V 
f ial 
2 fps (V full) by .65, the velocity of the total flow is then 
determined to be 1.3 fps. 


is found to be approximately .65. Multiplying 


Because this velocity is below the minimum required 
for self-cleaning, the sewer must either be placed on a steeper 
slope, to provide a velocity of 2 fps for the actual flow (in 
this case 11.0 ft. per thousand), or provision made for peri- 
odic flushing. In this example the latter will be assumed and 
velocity of 1.3 fps entered in column 16. Columns 17, 18, 
19, 20 and 21 can then be completed. The procedure out- 
lined above is now repeated for lines 2, 3, 4 and 5 of Table 3. 


Storm or Combined Sewers 


Velocity of Flow 


Storm and combined sewers are usually designed for a mini- 
mum velocity of 3 fps flowing full in order to prevent the 
deposition of solids. This is slightly more than the minimum 
required for sanitary sewers because street washings carry 
heavier particles into storm sewers. In computing the capac- 
ity of combined sewers, ordinarily no allowance is made for 


(2) cfs=Cu. ft. per second. 


(3) fps—=Ft. per second. 


domestic wastes as they represent less than five per cent of 
the total flow. 


Rational Method 


The so-called rational method is widely used in the design 
of storm or combined sewers. Eighty per cent of the engi- 
neers reporting in a survey conducted by Cornell University 
in 1944 used this method.* 

The rational method is based on the assumption that 
for any watershed the maximum rate of runoff for a given 
rainfall intensity occurs when all parts of the drainage area 
are contributing. It has evolved from attempts by engineers 
to solve the general expression Q=ciA** for the relation- 
ship between rainfall and runoff. The solution of this ex- 
pression by the rational method requires the following four 
general steps: 


a. The selection of intensity—duration rainfall curve 
suitable for local conditions. 


b. Determination of a runoff factor ¢ 


c. The location of proposed sewer line and inlets on a 
contour map and outlining the drainage areas tribu- 
tary to these inlets. 


d. Computation of the sewer sizes from these data. 


*For estimating the runoff from large areas (over 1000 acres) many 
engineers prefer the use of empirical formulas, such as McMath, 
Gregory, Parmley or Burkli-Ziegler in lieu of the rational method. 


** Where O 
c 
i 


A 


quantity of runoff in cfs 

coefficient of imperviousness 

intensity of rainfall in inches per hour 
contributing area in acres 


PAGE 17 


Placing a 24-in. concrete storm water sewer at Springfield, Ill. Airport 
in 1946. 


INTENSITY-DURATION OF STORMS. If enough 
local rainfall data are available the engineer may prepare a 
tabulation of storms of high intensity of rainfall and con- 
struct an intensity-duration curve such as the one shown in 
Fig. 6. If local rainfall records are not available a curve may 
be prepared from a study of data secured from nearby U.S. 
weather bureau stations, or from “Rainfall Intensity Fre- 
quency Data” by David L. Yarnell in Miscellaneous Publica- 
tions No. 204 issued by the U.S. Department of Agriculture 
(August 1935). 


In the preparation of such a curve, rates of rainfall 
(inches per hour) for various intervals of time (5, 10, 15 
minutes etc.) during the storm are plotted for the period 
covered by the available weather records. A curve connecting 
the points of maximum rate of rainfall is known as an inten- 
sity-duration curve for a maximum storm not expected to be 
exceeded in the period of years covered by the weather 
records. 


FREQUENCY OF MAXIMUM STORMS. It is desirable 
to provide sewers of sufficient capacity to carry the runoff 
for the largest storm of record. However, the cost of sewers 
large enough to carry the drainage from unusual storms is in 
most cases prohibitive. As a consequence, sewers are usually 
designed on the basis that their capacity will be exceeded an 
average of once in a certain number of years. It then becomes 
a problem of design to choose a storm frequency period that 
will provide sewers of a size economically suited to the needs 
of the area. 


Therefore, instead of connecting the points of the max- 
imum rate of rainfall as described above for a maximum 
storm, a similar curve connecting points which will be ex- 
ceeded once, twice, three times or more, is prepared. For ex- 
ample, if the available weather records cover a 20-year pe- 
riod and the points selected are exceeded once in the 20-year 
period, this is known as a 10-year frequency intensity-dura- 
tion curve; if exceeded twice, a 7-year frequency curve, and 
if three times, a 5-year frequency curve, etc. A 3- to 5-year 


PAGE 18 


frequency curve is commonly used in storm water sewer 
design. 

Usually a higher frequency curve is used in the design 
of branch and laterals than for main sewers. Relief sewers 
for the main lines usually can be constructed at a later date 
at less cost and inconvenience to the public than can relief 
sewers for branch or lateral lines. 


RUNOFF FACTOR. Theoretically the runoff factor (c) in 
the general equation varies from zero to unity depending 
upon: 


(1) percentage of impervious surface 
(2) character of soil 
(3) duration of rainfall 


(4) shape of tributary drainage area. 


The area of impervious surface tributary to the sewer can be 
readily computed. Future improvements which tend to in- 
crease the impervious area such as sidewalks, pavements and 
buildings must be estimated and included in the percentage 
of impervious surface. Impermeability factors as commonly 
used for various surfaces when dry and on flat slopes are 
shown in Table 4 on the following page. 

The porosity of the soil is an important factor. For ex- 
ample, sandy soil would absorb a much greater proportion of 
rainfall than clay soil. 

Maximum runoff will not occur until the entire surface 
is wet and all depressions filled. Therefore, the duration of 
the storm will affect the rate of runoff. 

The shape of the tributary area is not an important fac- 
tor except under unusual circumstances and ordinarily is not 
considered. 


Values generally assumed for this runoff factor are: 


Densely built up, downtown areas............ aseeeessoseeee a Ou 
Densely built up, residential areas (apartments)....0.50—0.70 
Less built up, residential areas (detached houses)....0.25—0.50 
Parklands, undeveloped districts..............000 v+oeee0.10—0.25 


AREA OF RUNOFF. The area A of surface runoff in the 
general formula is the only term in the expression O=c7A, 
which can be definitely determined. The area contributory 
to each sewer inlet can be plotted on a map and the tributary 
area definitely determined. 


TIME OF CONCENTRATION. The rational method of 
sewer design takes into consideration the time of concentra- 
tion; that is, the time required for water from the most fe- 
mote portion of the area to reach a certain point in the sewer. 
This is made up of two increments: (1) the time of flow on 
the surface from the most remote portion of the area to the 
first inlet, and (2) the time of flow in the sewer. 


QUANTITY OF RUNOFF. To determine the cubic feet 
per second runoff at any point along the sewer the rainfall 
intensity 7 (inches per hour) is obtained from the intensity 
duration curve for the total time of concentration up to that 


point. Then substituting this z in the formula Q=czA where 
A is area in acres and c is the runoff factor, the approximate 
cfs runoff (Q)* can be computed. 


Typical Example 


The hydraulic design of a storm sewer is best illustrated by 
an example. Suppose concrete circular sewers are required 
for the area indicated in Fig. 7. Manholes are located along 
the line of the proposed sewer at intermediate intervals of 
about 300 ft. and at all street intersections. Areas contribu- 
tory to each manhole are drawn and computed. Rainfall in- 
tensities are taken from the curve shown in Fig. 6. 


ASSUMPTIONS. Runoff factor c=0.40 (uniform value 
for this example) 

Minimum velocity=3 fps (flowing full) 

Minimum size of storm sewer=10 in. 

Time of concentration =10 minutes to first manhole. 
SOLUTION. The hydraulic properties of the storm sewer 
as they are determined will be entered in Table 5. The design 
of the sewer system is begun at the uppermost manhole, in 
this instance at manhole 7. The area contributing surface 
runoff water to manhole 7 is found to be one acre. This is 
entered in column 4, line 1, of Table 5. 

The time of concentration which is the time it takes 
water from the most distant point to reach the uppermost 
manhole has been assumed as 10 minutes, (column 6, line 1). 
It will be found from the curve in Fig. 6 that the intensity 
of rainfall for this period of time is 4.2 in. per hour (column 
8, line 1). 


*To be exact, ciA should be multiplied by a correction factor of 
1.01. However, this refinement is not considered justified in most 
cases. 


1.0 


60 


TABLE 4 


PERCENTAGES OF IMPERVIOUSNESS 
FOR VARIOUS SURFACES 


TYPE OF SURFACE IMPERMEABILITY 

Watertight surfaces (such as roofs and concrete, 

asphalt and tightly sealed block pavements) ...... 70—95% 
Block pavements with open joints................ 50—70% 
Macadam pavementseae nein rene re | 25—60% 
Gravel pavements s.-eamas fo ee eta a ee | 15—30% 
Parks, cultivated lands, lawns, etc., depending on 

slope of surface and character of soil............ 5—20% 
Wooded areasiaer scere trite iaete ater ara ee 1—20% 


The next step is to determine the quantity of runoff as 
given by the formula, Q=c7zA. Substituting the value of 
c=0.4 and 1=4.2 and A=1 acre in the above formula, we 
find that the runoff in cfs is approximately 1.68 cu.ft. which 
is entered in column 9, line 1. Next, enter the left-hand edge 
of Fig. 1, page 9 at a point representing 1.68 cfs and go 
parallel to lines running diagonally upward to the right until 
an intersection is obtained with a vertical line representing 
a velocity of 3 fps. The projection of this point of intersec- 
tion to the right indicates that a 10-in. circular sewer will be 
required (column 11, line 1). The projection of this point 
upward to the left indicates that the slope of the sewer will be 
approximately 51 ft. per thousand (column 10, line 1). 
Columns 12, 13, 14, 15 and 16, line 1 can then be filled in. 
The time of the flow from manhole 7 to 6 may be found in 


Constants A&b for curve shown are Meyer's constants 
for a 2-year frequency storm for regional-group 2, 


Intensity in inches per hour-”i” 


en 
je) 


> 
iS) 


ad 
oO 


nN 
jo) 


as shown in Tables 17 


18 on page BGI of Davis’ 


"Handbook of Applied Hydraulics” 


1942 Edition. 


40 50 6O 10 80 
Duration of rain in minutes-“t’’ 


FIGURE 6—Intensity-Rainfall Curve 


90 


100 


Ke) 


120 


PAGE I9 


204 


“208_~ 
2007 


me === 


7 y Y ee 


7 2.40Ac Bh 2.96Ac 
van Sr: Sree 
aa 


2006 d 


208 


FIGURE 7—Plan for Storm Sewer Example 


the lower right-hand corner of Fig. 1. The intersection of a 
line representing a velocity of 3 fps and a diagonal line repre- 
senting the length of the sewer in the section (300 ft.) pro- 
jected horizontally to the right shows a time of flow in the 
section of 1.7 minutes. That is then entered in column 7, 
line 1. This increment of time added to the total of concen- 
tration assumed at manhole 7 gives a total time of concen- 
tration of 11.7 minutes at manhole 6. This value is then 


TABLE 5 


Tributary Time of flow 


Sewer location 3 Z 
area in minutes 


Line number 


Rate of} Runoff 


entered in column 6, line 2. From Fig. 6 it is now determined 
that for this concentration period of 11.7 minutes the in- 
tensity of rainfall is about 4 in. per hour. This is entered in 
column 8, line 2. 

The area contributing to the runoff at manhole 6 is an 
increment of 2.28 acres (column 4, line 2) plus the previous 
total of 1 acre making a total of 3.28 acres which is entered 
in column 5, line 2. The procedure outlined in the preceding 


COMPUTATION SHEET FOR HYDRAULIC PROPERTIES OF STORM SEWER 


Sewer design Profile 


Elevation 
of invert 


Upper | Lower 
end end 


Diameter 
in inches 
Capacity 
in cfs. 
Velocity in 


15 16 


_ 
wW 


3.7 12.79 


3.5 16.55 


3.4 | 40.34 


PAGE 20 


paragraphs is repeated for line 2 and all succeeding sections 
of the sewer, as shown in Table 5. 

The use of a method* which takes into consideration 
the losses due to infiltration, storage, evaporation, etc. has 
been advocated as being more accurate than the rational 
method. Such a method would require considerable data on 
the amount of hourly variations of rainfall as well as infor- 
mation and data on evaporation, and infiltration capacity of 
the soil. Such a method is more applicable for use in large 
projects involving large expenditures. It is generally not 
warranted in smaller projects. 


Cast-In-Place Sewers 


Reinforced concrete has been used in the majority of the 
large sewers which have been constructed in this country. 
This material is particularly suited for cast-in-place construc- 
tion because of its adaptability, homogeneity, strength and 
durability. 

Of the many cross-sections which have been proposed, 
rectangular, parabolic, horseshoe or semi-elliptical sections 
have been the most frequently used in the construction of 
cast-in-place concrete sewers. The section selected depends 
upon the hydraulic requirements of the sewer and the con- 
ditions at the installation site. Two examples of cross-sections 
which have been employed are illustrated in Fig. 8. 


HYDRAULIC REQUIREMENTS. Since the hydraulic 
radius of a circle is greater than that for any other section 
of equal area, the largest flow for the same cross-sectional 
area is that of a circular section. If the sewer in question is 
a combined sewer which must have considerable capacity for 
storm flows but will carry fairly low flows during several 
months of the year, a section other than circular may be 
desirable. 

The sewer must also be structurally stable, must fit the 
space available, must be suited to the method of construc- 
tion, and the cost must be reasonable. A more complete dis- 
cussion of the structural design of concrete conduits and 
sewer sections will be found in Concrete Culverts & Conduits 
and Analysis of Arches, Rigid Frames and Sewer Sections.** 
The sewer may be located near buildings, or beneath road- 
ways and require a special shape. For example, box-type 
sewers have been used where there is limited head room, or 
sections similar to Fig. 8 (B) might be suitable for construc- 
tion in narrow, deep trenches. 


“W. W. Horner and S. W. Jens, “Surface Runoff Determination 
from Rainfall Without Using Coefficients”, ASCE Proceedings, Vol. 
67, 1941, page 533. 


**Both of these booklets are published by the Portland Cement 


Association and are available free on request. Distributed only in 
U.S. and Canada. 


A. Circular Concrete Sewer 


B. Parabolic Concrete Sewer 


FIGURE 8 —Typical Cast-in-Place Cross-Sections 
of Sewers 


PAGE 21 


CHAPTER 6 


LOADS ON SEWERS 


N ADDITION to determining the size of the sewer to 
carry the expected flow, the sewer structure itself must 

be designed to withstand external loads to which it may be 
subjected. These can be divided into two parts: (1) loads 
caused by backfill and (2) surface loads caused by other dead 
or live loads which may be transmitted to the sewer structure. 


Loads Caused by Backfill 


Loads resulting from backfill material on underground con- 
duits have been the subject of considerable research during 
the past 40 years. The major part of this research has been 
conducted by Marston, Spangler and their associates at lowa 
State College. Results of this research have been reported 
from time to time in various technical publications.* 


Natural ground surface 


Surface of embankment 
4 rox 77 7 “y 


(a) Trench type (b) Projecting type 


FIGURE 9—Types of Conduits 


Underground conduits have been grouped into two gen- 
eral classifications known as (1) “ditch or trench conduits” 
and (2) “projecting conduits”; depending upon the manner 
in which they are installed (see Fig. 9). 


*Bulletin No. 31 (1913), Engineering Experiment Station, Iowa 
State College; Bulletin No. 112 (1933), lowa Engineering Experi- 
ment Station, Iowa State College; ASCE Transactions, Vol. 113 
(1948), page 316; Loads on Underground Conduits, published by 
American Concrete Pipe Association; Highway Research Board 
Proceedings, Vol. 26 (1946), page 189. 


PAGE 22 


Sewers, drains and watermains when they are installed 
in comparatively narrow ditches in undisturbed soil are good 
examples of trench conduits. Culverts which project above 
the normal ground surface when they are installed and then 
covered by an embankment are examples of projecting con- 
duits. Projecting (embankment) conduit conditions also pre- 
vail whenever the width of excavation in trenches at the top 
of a conduit exceeds two or three times the width of the 
conduit. 


Trench Conduits 


Marston developed formulas for determining the backfill load 
on underground conduits for both trench conduits and pro- 
jecting conduits. The formula for rigid conduits of the trench 
type is 

W,=C,wB) 
where W,=the load on the conduit in lb. per lin.ft.; 

C,=a coefficient; 

w=weight of soil in lb. per cu.ft.; 
and B,=width of trench in ft. at top of conduit. 


The coefficient, Cz, depends upon the coefficient of internal 
friction of the fill material (4); coefficient of sliding friction 
between the fill material and the sides of the trench (p’); 
and the ratio of active lateral pressure to vertical pressure, 
(K)* as used in Rankine’s formula; and the ratio of height 
of fill in feet over top of conduit (H), to the width of trench 
(Bq). All of the factors with the exception of Cq can be 
readily and fairly accurately ascertained. Cg is a rather compli- 
cated expression involving physical characteristics of the soil. 
Values of Ca can readily be determined from Fig. 10 for 
H 


values of Ku or Kp’ as shown when — is known. 
d 


BEDDING METHODS. The load carrying capacity of a 
precast conduit is increased by the application of a load fac- 
tor** determined from the method and manner of bedding. 
Four methods or classes of trench bedding have been pro- 


og = Ew 

Vert l+p 
**The load factor is a ratio of the supporting strength in the field to 
the strength as determined by the ASTM 3-edge bearing test. 


de 


VALUES OF 


By 
CROGA MIEN 


s SECS RODERIEI 
BUISTeeeeeEee Co 
See Gssose 60>) nanere By aon. 
COT oe 
Pitter He typ Bpae sanes 
BB SHSSTRRAGHAGALTAALA! CARODIT BOT BHORGR RR ORRRE 
MRO REGR CLARO RRCE! COONEES DETR OE SOE 
BORER RATRSOCE OCT CSRDAIE OE BRAP ARO 


init 
SOGHRGAGGGUORSERAUIE INIININ (NH AGU E AGNE'.QOODODSUIEOOIIINNNIG 


: 
SESSEETcireensariciint a 


pee 


Pertti fy 
coe 
BSssacoreReLews 
SEeceanees 
sassttes 


HH 


iS 
= 
eat 


Seco 
Saccsc. comoses: 
te | 


4 b 
ene esd: 

Ar eee esas 

L 9 .48°/0°.09 s800080000008%,"4.8 888 eaene 

SSS 488's87.e GORSRRGNC0Ry. “sc. BR SREReaeenees 

ATE Beenenseenn’ "a [| eae8 


V.60 ai | 
LLY | a% HH ag 


VAT YT 


r | 
Ba 
71 


a8 Pitter ttt tp bp tee bt pet bs 


NSSSG0ER8 
y COC 
Pe eh bela HOS 
PTT TT Tg WS Fr MNT 
PET 

1S 20 .26 3 4 56 6 


Values of Coefficient —C, 


A=C, for Ku and Kp’=.1924 for granular materials without cohesion 
B=C, for Ku and Ku’=.165 max. for sand and gravel 
C=C, for Ku and Ky’=.150 max. for saturated top soil 


D=C, for Ky and Ky’=.130 ordinary max. for clay 
E =C, for Ku and Kp’=.110 max. for saturated clay 


Load Per Unit of Length, W.=C,wB,” 


w= unit weight of fill materials 


Ba= breadth of trench at the top of conduit 


H= height of fill over top of conduit 


rf 


VALUES OF 


FIGURE 10—Computation Diagram for Earth Loads on Trench Conduits (completely buried in trenches) 


PAGE 23 


Left—Shaping bottom of trench with templet to conform to lower part of conduit exterior. Photo courtesy Bureau of Reclamation. Right—Tamping 
backfill material around and adjacent to pipe conduit at Springfield, Ill. Airport in 1946. This adds support to the conduit and increases its struc- 


tural capacity. 


posed as follows: 


Class A—Concrete cradle 
Class B—First class 

Class C—Ordinary 

Class D—Impermissible 


Class A, or concrete cradle trench bedding (Fig. 11a), is that 
method in which the lower part of the exterior of the con- 
duit is set in a plain or reinforced concrete foundation of 
suitable thickness and extending upward on each side for a 
greater or less proportion of its height, not less than 25 
per cent. 

Class B, or first class trench bedding (Fig. 11b), differs 
from ordinary bedding in that the conduit is set on fine 
granular materials in an earth foundation shaped to conform 
to the lower part of the conduit exterior for a width of at 
least 60 per cent of its external diameter. The trench is then 
backfilled with granular materials hand placed and tamped 
in 6-in. layers to fill completely all spaces under and adjacent 
to the conduit for a distance of at least 1 ft. above the top of 
the conduit. 

Class C, or ordinary trench bedding (Fig. 11c), is that 
method in which the conduit is placed with ordinary care 
in an earth foundation shaped to fit the lower part of the 


Crass D CLass C 


ORDINARY BEDDING 
LOAD Factor=1.5 


IMPERMISSIBLE BEDDING 
Loab FAcTor=I.| 


d c 


conduit exterior for a width of at least one-half its external 
diameter. The ditch is then backfilled to a height of at least 
one-half foot above the top of the conduit with granular 
materials, shovel placed and tamped so that all spaces under 
and adjacent to the conduit are filled. 

Class D, or impermissible trench bedding (Fig. 11d), is 
defined as that in which little or no care is exercised to shape 
the foundation to fit the lower portion of the conduit or to 
refill all spaces under and around the conduit. This is not a 
recommended type of bedding and is to be avoided when- 
ever possible. 


LOAD FACTORS. The load or bedding factors for these 
four classes of bedding have been determined experimentally 
at Iowa State College to be approximately as follows: 

Class of Bedding 
A—Concrete cradle 
B—First class 1.9 
C—Ordinary las 
D—Impermissible pl 


Bedding or Load Factor 
2.25—3.4 


SAFETY FACTORS. For wnreinforced concrete pipe 
(ASTM C14-58) it is suggested that a safety factor of 1.25 
—1.50 be applied to the average ultimate load causing failure 


Crass B CrassA 


Ba 


Thoroughly 2000# Concrete 
tamped or better 


Min= % inside dia NI 
CONCRETE CRADLE BEDDING 
Loap FacTor=7?.2-3.4 


First CLass BEDDING 
Loab Factor=!.9 


b a 


FIGURE I!—Bedding Methods for Trench Conduits 


PAGE 24 


as determined by the 3-edge bearing method of test as speci- 
fied by the ASTM. For reinforced concrete pipe (ASTM 
C75-55 and C76-57T) a safety factor of 1.0 is considered 
adequate if applied to the load required to produce a 0.01-in. 
crack as determined by the 3-edge bearing method because: 


(1) this load is considerably less than the ultimate load at 
failure; 


(2) concrete increases in strength with age; 

(3) other design variables usually are ultraconservative. 
PERMISSIBLE DEPTHS OF CUT. Tables 6 to 9 show 
the approximate permissible depths of cut to bottom of con- 
crete pipe using the Marston Formula for various classes of 
concrete pipe, bedding and backfill material as indicated. The 
values given in these tables are computed on the strength of 
the concrete pipe* multiplied by the load factor and divided 
by the safety factor as indicated. Each table represents one 
type and weight of backfill material with the value of Ky as 
shown. The loads on a conduit will vary directly as the weight 
of the backfill material, providing all other factors remain 
constant. The backfill material shown in Table 9 is one of the 
best while that shown in Table 6 is one of the poorest. 
Tables 7 and 8 represent other intermediate materials. 


BACKFILL LOADS. Tables 10 to 13 indicate total backfill 
Joads in pounds per lin.ft. on conduit for depths and widths 
of trench as shown based upon the same formulas and soil 
conditions used in computing Tables 6 and 9. The loads 
shown in Tables 10 to 13 must not exceed the safe supporting 
strength of conduit. This, for reinforced concrete pipe, is 
the minimum load which will produce a 0.01-in. crack as 
determined by the 3-edge bearing method multiplied by the 
bedding factor; and for unreinforced pipe, it is the wltzmate 
load, as determined by the 3-edge bearing method, multi- 
plied by the bedding factor and divided by the safety factor 
(see Table 18, page 48, and Table 18A, page 49). It is evi- 
dent that the load increases rapidly as the width of trench 
at the top of pipe (B,) increases. The importance of keeping 
the trench width to a practical minimum is apparent. 

In wide ditches caused by caving, the load on the pipe 
is increased because the width of the trench at the level of 
the top of the pipe (Bz) is increased. If sheeting is used and 
left in place, the coefficient of sliding friction (4’) may be 
reduced. Any reduction in the value of py’ increases the load 
on the conduit. The value of p’ may also be reduced if the 
sheeting is pulled after a considerable depth of the backfill- 
ing material is in place. In the latter case the fill material may 
not move into the entire space vacated by the sheeting, thus 
preventing the full value of p’ to be developed. However, if 
the sheeting is pulled as the trench is backfilled the full value 
of »’ probably will be attained and the load will be the same 
as that computed for a width of trench equal to the distance 
from back to back of the sheeting. 


Projecting (Embankment) Conduits 


The formula for backfill loads on the rigid type projecting 
conduits as developed by Marston is 


*Determined by the 3-edge bearing method of test. 


We=C we! 
where W_.=the load on the conduit in lb. per lin.ft.; 
C,=a coefficient; 


w=the unit weight of the backfill material in Ib. 
per cu.ft.; 
and B,=the external breadth of the conduit in ft. 


The coefficient C, is dependent upon (1) the ratio of height 


of fill to horizontal breadth of conduie (7) (2) the co- 


efficient of internal friction of the backfill Parerial Cie (oO) 
the projection ratio (p); and (4) settlement ratio (rsa). The 
effect of these will be briefly discussed. 

(1) For each size of conduit, the ratio of height of fill 
to the breadth of conduit varies directly with the height of 
fill. (2) The coefficient of internal friction (uw) will vary from 
0.3 to 1.0. However, this factor does not have a great deal of 
influence on the load and so a value of 0.6 for u can be 
assumed for any type of soil without involving any great 
error. (3) The projection ratio (p) is defined as the vertical 
height from the top of the conduit to the original ground 
surface, divided by the breadth of the conduit (B,). In case 
the ground slopes away from or toward the conduit, the 
vertical height from the top of the conduit to the original 
ground surface is assumed as the average height over a 
horizontal distance on each side equal to its breadth. (4) The 
settlement ratio (7sq) for rigid conduits is assumed as 

Aa laie) th G 
A 

Where A=the amount of the settlement of the fill mate- 

rial along side of the conduit between the 
natural ground line and the top of pipe; 

B=the amount of settlement of the natural 
ground line adjacent to the conduit; 

and C=the amount of settlement of the conduit itself. 
The following tentative values of settlement ratio are rec- 
ommended for use in the design of rigid projecting conduits: 

(1) r,;=1.0 for rock or unyielding soil foundation 

(2) r,,=0.5 to 0.8 for ordinary soil 


(3) r,,=0.0 to 0.5 for yielding foundation as compared 
to the adjacent natural ground 


The coefficient C, can be determined for any value of z 


Cc 


from Fig. 12, page 32, by using the curve corresponding to 
the product of the settlement ratio (sq) and the projection 
ratio (p). 
BEDDING METHODS. The method and manner of bed- 
ding of a projecting conduit is also an important factor 
which increases the load carrying capacity of the conduit. 
Classes of bedding for projecting conduits are as follows: 

Class A, or concrete cradle projecting conduit bedding 
is that method in which the lower part of the conduit ex- 
terior is bedded in a plain or reinforced concrete cradle 
having a minimum thickness under the conduit of at least 
one-quarter of its nominal internal diameter and extending 
upward on each side of the conduit for a height equal to 
one-quarter its outside diameter. The concrete shall have a 
compressive strength of at least 2000 psi at 28 days. 

Class B, or first-class projecting conduit bedding, is that 
method where the projection ratio is not greater than 0.70 


PAGE:25 


TABLE 6 


PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR SATURATED CLAY 
(Ku=0.110 and w=130 lb./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included 


Bedding Internal diameter of pipe (in inches) 
ASTM SPECS NO. a 
Class Factor 4’ 6” 8” 10” 12” 15” 18” Say ll 24” 7a 30” 390 36” 42” 48” 54” 60” 66” 72" 
C14-58 D 4 4 5 5 5 5 6 6 6 
Conc. sewer pipe G 69 6° 8797 / Oe SaaS es 
Safety factor = 1.5 B 10 9 10 10 9 10 10 10 10 
A *NL 34 34 24 20 19 19 18 17 
C75-55 D On 9 OS BSS in 9 19 ie 9 eae 9. 8 9 9 10 10 11 11 
Reinf. conc. sewer pipe Cc 14°13 «#13 «13 ~«12«212 ~«1710~=« «12 «1006 (610) 112 ea 2s 
Safety factor = 1.0 B 21 19 18 18 15 15 15 15 13 13 13> 13 Apa 
A NL NL NL 57 33 31 27 26 20 19 19 19 20 20 20 
C76-55 D L223 11 11 10 11 «#12 «12: 139 1S eas 
Std. strength reinf. Cc PAY FN 74] 15 14 13 14 15 16 16 16 16 
conc. culvert pipe B NL 44 38 21 19 17 18 19 19 19 19 19 
Safety factor = 1.0 A NL NL NL NL 45 30 31 32 31 29 28 28 
C76-55 D 15 16 14 16 17 #17 17) 17 ile 
Extra strength reinf. G 23 24 20 21 22 23 22> 22522 
conc. culvert pipe B 39 38 27 28 29  30)°28)°27 327 
Safety factor = 1.0 A NL NL 79 72 68 66 51 48 45 
*NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (W,=CawBa) based on a safety factor as noted and on the 


assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in. = 
B.+16 in.; for internal diameters of 36 in. and over = B.+24 in. 


TABLE 7 


PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR SAND AND GRAVEL 
(Ku=0.165 and w=120 lb./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included 


Bedding Internal diameter of pipe (in inches) 
ASTM: SPECS NO) —————— 
4” 6” 8” 10” 12” 15” 18” 21” 24” 27" 30” aau 36” 42” 48” 54” 60” 66” 72 


C14-58 
Conc. sewer pipe 
Safety factor = 1.5 


69765 56m) (6 3560.6 e/a, 
12 10 11 10 9 9 10 10 10 
*NL NL 64 18 15 14 14 13 13 
NEL NL NL NL NL NL NL NL 41 


C75-55 D 13 12 12 11 10 10 10 10 9 9 10 10 11 11 «12 
Reinf. conc. sewer pipe (e NL 27 21 19 15 15 14 14 12 12 12 13) 13 303aei4 
Safety factor = 1.0 B NL NL NL NL 24 23 20 19 15 15 15 15 15 16 16 

A NL NL NL NL NL NL NL NL 29 26 24 24 24 23 23 
C76-55 D 26 23 21 14 13 12 13 14 14 14 #14 «14 
Std. strength reinf. G NL NL NL 24 20 16 17 18 18 18 18 18 
conc. culvert pipe B NL NL NL NL 34 22 23 24 24° 22522522 
Safety factor = 1.0 A NL NL NL NL NL NL 223 67 53 42 38 36 
C76-55 22 23 18 19 20 21 19 19 19 
Extra strength reinf. NL NL 29 30 30 30 27 26 25 
conc. culvert pipe NL NL 66 57 52 48 38 36 34 
Safety factor = 1.0 NL NL NL NL NL NL NL NL1I101 

*NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (We=CawBa) based on a safety factor as noted and on the 


assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= 
B. +16 in.; for internal diameters of 36 in. and over=B,+24 in. 


PAGE 26 


TABLE 8 


PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR WET TOP SOIL 
(Ku=0.150 and w=110 Ib./cu.ft.) Ditch Conduit Conditions— Surface Loads Not Included 


neers eee ee ee ee ee ee ae ee ".. 
Bedding Internal diameter of pipe (in inches) 


ASTM SPECS NO. 


Class | Factor 


4’ 6” 8” 10” 12” 15” 18” 21” 24” 27" 30” ce te We 36” 42” 48” 54” 60” 66” 72" 


657°6917616. 6 7 60 7. 7 7 
12 10 11 9 10 10 10 10 10 
*NL NL 32 19 15 15 14 14 13 
NL NL NL NL NL NL NL NL 39 


a  — 


C14-58 
Conc. sewer pipe 
Safety factor = 1.5 


>wOaTO 
OS ae 
oon 


C75-55 D 1.1] el eR) (be 4b> Uh The RP Ge ae ae) ee A) es 
Reinf. conc. sewer pipe| C Is NL 28 22 20 16 16 15 15 12 12 13 13 14 14 14 
Safety factor = 1.0 B EY NL NL NL 69 25 23 21 20 16 15 15 16 16 16 17 

A 3.0 NL NL NL NL NL 30 27 25 24 24 24 24 


C76-55 

Std. strength reinf. 
conc. culvert pipe 
Safety factor = 1.0 


14 13 12 13 14 15 14 15 15 
25 21 17 S1SGR19 2 1OM 19S 19 19 
NL 35 23 24 25 24 23 23 23 
NL NL NL 87 69 54 44 40 38 


>wWOOD 
ON ae 
omone me 


23 24 18 20 21 21 20 20 20 
NL NL 30e3 lees lan 2 = 282727, 
NL NL 67 58 54 50 40 37 35 
NL NL NL NL NL NL NL NL 99 


C76-55 

Extra strength reinf. 
conc. culvert pipe 
Safety factor = 1.0 


*NL=No limit to bottom of pipe. Note: This table is computed by the Marston formuia (W.=CawBdq) based on a safety factor as noted and on the 
assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= 
B,+16 in.; for internal diameters of 36 in. and over=B,+24 in. 


TABLE 9 


PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE 
FOR GRANULAR MATERIALS WITHOUT COHESION 


(Ku=0.1924 and w=100 Ib./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included 


Bedding Internal diameter of pipe (in inches) 


ASTM SPECS NO. 
4” 6” 8” 10” 12” 15” 18” 9 dy | 24” 27" 30” 334 36” 42” 48” 54” 60” 66” 7 fal! 


C14-58 D TLR 910T 98s S59 a9 9 
Conc. sewer pipe e *NL NL NL NL 17 16 15 14 13 
Safety factor = 1.5 B NL NL NL NL NL NL NL 26 21 
A NL NL NL NL NL NL NL NL NL 
Uh lo a a eee ee 
C75-55 D el NL 28 20 17 14 14 13 13 11 #11 «191 «12 «12 #13 «213 
Reinf. conc. sewer pipe G es NL NL NL NL 31 25 21 20 15 15 14 15 15 15 16 
Safety factor = 1.0 B ihe? NL NL NL NL NL NL NL 35 20 19 18 18 19 19 19 
A 3.0 NL NL NL NL NL NL 52 37 34 33 31 30 
= iets eh he ee 
C76-55 D Ue 22 18 15 16 17 17 16 16 17 
Std. strength reinf. G les NL NL 23 24 24 24 22 22 22 
conc. culvert pipe B 1.9 NL NL 40 38 38 34 30 28 27 
Safety factor = 1.0 A 3.0 NL NL NL NL NL NL NL101 63 


C76-55 NL NL 27 27 28 28 25 24 24 
Extra strength reinf. NL NL NL NL 80 60 41 37 34 
conc. culvert pipe NL NL NL NL NL NL NL 70 54 
Safety factor = 1.0 NL NL NL NL NL NL NL NL NL 
*NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (Wc=CawBj) based on a safety factor as noted and on the 


assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= 
B, +16 in.; for internal diameters of 36 in. and over =B,+24 in. 


PAGE 27 


TABLE 10 


APPROXIMATE MAXIMUM BACKFILL LOADS?*% (in Ib. per lint. ON CONCRETE DITCH CONDUITS 
Saturated Clay (Ku=0.110 and w=130 lb./cu.ft.) 


WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) 


H® : , 
2 | 3 4 | 5 6 7/ 8 | 9 10 
4 800 ‘1,300 1,900 2,400 3,000 3,400 4,000 | 4,500 5,000 
é.| 1,100 | 11,900 | 2,600 3,400 4,300 5,100 | 5,900 6,800 7,400 
8 1,300 2,400 3,300 4,400 5,400 6500 7,600. ~—~-8,700 9,800 
10 | 1,500 | 2,800 4,000 5,200 6,600 7,800 9,100 10,500 12,000 
Taeien 11-700 ele? 100 4,500 6,000 7,500 9,100 10,700 12,200 13,900 
14 | 1,800 | 3,300 5,000 6,800 8,500 10,300 12,100 | 14,100 15,900 
Veni 81-9005 Hees 600 5,500 7,400 9,400 11,500 13,400 salle 16.600 17,700 
18 2,000 += 3,900 = 5,900 8,000 10,200 12,600 14,700 17,100 19,400 
20 | 2,100: | 4,100 | 6200 | 98,600 11,000 13,500 16,000 ‘18,400 21,000 
25 2,200 4,400 7,000 9,700 12,600 15,700 18700 21,800 25,000 
30 2,300 4,700 7,600 | 10,800 14,000 17,500 21,200 | 24,800 28,400 


©H =depth of fill to top of conduit (in ft.). 


and in which the conduit is carefully bedded on fine granular 
material in an earth foundation carefully shaped to fit the 
lower part of the conduit exterior for at least 10 per cent 
of its overall height. The earth fill material is thoroughly 
rammed and tamped in layers not more than 6 in. deep 
around the conduit for the remainder of the lower 30 per 
cent of its height. In case of rock foundation, the conduit 
is bedded on an earth cushion having a thickness under the 


TABLE II 


*Note: By the Marston formula (W.e=Caw Bi); surface loads not included. 


conduit of not less than 0.5 in. per ft. of height of fill over 
the conduit with a minimum allowable thickness of 8 in. 
and with earth foundation carefully shaped and filled around 
the conduit, as described in preceding sentence. 

Class C, or ordinary projecting conduit bedding is that 
method in which the conduit is bedded with ordinary care 
in an earth foundation shaped to fit the lower part of the 
conduit exterior with reasonable closeness for at least 10 


APPROXIMATE MAXIMUM BACKFILL LOADS?* (in Ib. per lin.ft.) ON CONCRETE DITCH CONDUITS 
Sand and gravel (Ku=0.165 and w=120 lb./cu.ft.) 


WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) 


(1) — = —————— 7 — == 
H? | | 


| 2 re a j 4 ¥ | 5 6 7 8 9 | 10 

4 | 700 1,100 1,600 | 2,100 2,600 3,100 | 3,500 4,000 4,400 

6 | 900 1,500 2,200 | 2,900 3,600 4,400 5,000 5,800 6,600 

8 | 1,000 1,900 | 2,800 | 3,700 4,600 5,500 6,500 7,500 8,400 
10 1,200 2,200 | 3,200 | 4,300 5,500 6,600 7,800, | 8,900 10,200 
12 1,200 2,400 3,600 | 4,900 6,300 7,600 9,000 | 10,400 11,800 
14 1,300 2,500 4,000 5,400 7,000 8,500 | 10,100 11,700 13,300 q 
16 1,300 2,700 | 4,200 3,700 7,600 94007 Ve 411,100.57 * 13,000 14,800 
18 1,400 Se 2. 600= S68 4500 6,300 8,200 10,100 | 12,000 | 14,100 16,200 
20 1,400 | 2,900 | 4,700 6,600 8,700 10,800 13,000 | 15,200 17,400 
25 1,400 | 3,000 5,100 7,300 9,700 12,200 14,900 | 17,600 20,300 q 
30, 1,400 3,100 5,300 7,800 10,600 13,400 16,500 | 19,500 22,800 4 


HH = depth of fill to top of conduit (in ft.). 


PAGE 28 


*Note: By the Marston formula (We=Caw Bj); surface loads not included. 


TABLE 12 


APPROXIMATE MAXIMUM BACKFILL LOADS* (in bb. per lint.) ON CONCRETE DITCH CONDUITS 
Saturated Top Soil (Ku=0.150 and w=110 Ib./cu.ft.) 


zs WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) 
2 3 4 5 6 7 8 2) 10 

4 600 | 1,100 1,500 2,000 2,400 2,800 3,200 3,600 4,000 
. 6 900 1,500 2,100 2,800 3,500 4,100 4,700 5,400 6,000 
8 1,000 | 1,800 2,600 3,500 4,300 5,300 6,200 7,000 7,900 
10 1,100 | 2,100 3,100 4,100 5,200 6,300 7,300 8,400 9,600 
12 1,200 2,300 3,500 | 4,800 6,000 7,300 8,500 9,800 11,100 
14 1,300 2,500 3,800 5,300 6,700 8,100 9,600 11,100 12,600 
16 1,300 2,600 4,100 5,700 7,300 9,000 10,600 12,300 14,000 
18 1,300 2,700 4,400 6,100 7,900 9,700 11,600 13,400 15,400 
20 1,400 2,800 4,600 6,500 8,500 10,500 12,500 14,600 16,600 
25 1,400 3,000 5,000 7,200 9,500 11,900 14,400 17,100 19,600 
30 1,400 3,100 5,300 7,700 10,400 13,200 16,000 19,100 | 22,000 


@H =depth of fill to top of conduit (in ft.). 


per cent of its overall height. The remainder of the conduit 
is surrounded by granular materials placed by shovels to fill 
all spaces completely under and adjacent to the conduit. In 
case of rock foundation the conduits are bedded in an earth 
cushion having a depth as provided under class B bedding, 
and with the earth foundation carefully shaped and filled 
around the conduit as described in the preceding sentence. 

Class D, or impermissible projecting conduit bedding, 


MABLE 13 


*Note: By the Marston formula (Wce=Caw Bj); surface loads not included. 


is that method in which little or no care is exercised either 
to shape the foundation surface to fit the lower part of the 
conduit exterior or to fill all spaces under and around the 
conduit with granular materials. This type of bedding also 
includes rock foundation in which an earth cushion is pro- 
vided under the conduit, but is so shallow that the conduit, 
as it settles under the influence of the vertical load, ap- 
proaches contact with the rock. 


APPROXIMATE MAXIMUM BACKFILL LOADS* (in Ib. per lin.ft.) ON CONCRETE DITCH CONDUITS 
Granular materials without cohesion (Ku=0.1924 and w=100 lb./cu.ft.) 


- WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) 
: 2 | 3 4 | 5 ] 6 | 7 8 9 10 
4 500 | 900 1,300 1,700 2,100 2,500 2,900 3,200 3,600 
6 700 | 1,200 1,800 2,400 2,900 3,500 4,100 4,700 | 5,300 
8 800 | 1,500 2,200 2,900 3,700 4,400 5,200 6,000 | 6,800 
10 900 | 1,600 2,500 3,400 4,400 5,300 6,200 7,200 8,200 
12 900 1,800 2,800 3,800 4,900 6,000 7,200 8,300 9,700 
14 900 1,900 3,000 4,200 5,500 6,700 8,000 9,300 10,600 
Z 6 1,000 2,000 3,200 - 4,500 6,000 7,400 8,800 10,300 11,700 
18 1,000 2,100 3,400 4,800 6,300 8,000 9,600 11,200 12,800 
20 1,000 2,100 3,500 5,000 6,700 8,400 10,200 12,000 13,800 
25 1,000 2,200 3,800 5,500 7,400 9,300 11,600 13,700 16,000 
30 1,000 2,300 3,900 | 5,900 8,000 10,200 12,600 15,100 17,700 
ee ee ee ees en ee eee Ee eee eee 


®H = depth of fill to top of conduit (in ft.). 


*Note: By the Marston formula (W.=Caw Bi); surface loads not included. 


PAGE 29 


LOAD FACTOR. The load or bedding factors for project- 


ing conduits are expressed by the formula: te 


Where L,;=the load factor, 


N=a factor which is a function of distribution of 
vertical load and vertical reaction and, there- 
fore, varies with the class of bedding; (see 
Table 14). 


x=a factor which is a function of the area of 
the vertical projection of the conduit on which 
the active lateral pressure of the fill material 
acts (see Table 15). 


q=the ratio of the total lateral pressure to the 
vertical pressure, expressed by the formula 


PB. 
(114 Pe) ok. EKA 
2 


praia en Fs 7 prc. \ BE: 


When the load and reaction situation causes the pipe to 
crack first at the top (usually the case when pipe are bedded 
in concrete cradle) values of x’ should be substituted for x 
in formula for load factor. 


Table 16 shows values of load factor for the four classes 
of bedding for a fixed value of K and varying with the ratio 
of height of embankment over the pipe to the external 
breadth of the conduit and for various projection and settle- 
ment ratios. It will be noted that there is not much difference 
in the load factor when the settlement ratio r;g=0.2 and 
when 7;g=0.7. Therefore, values of 7g between 0.2 and 0.7 
can be determined for all practical purposes by interpolation 
and beyond 0.7 by extrapolation. If more accurate values of 
the loading factor for various values of rq are desired they 
can be computed from the equation for load factor (Ly) given 
above. The safe load that can be carried by the conduit is de- 
termined by applying the proper safety factor (see page 24) 
to the load carrying capacity of the pipe conduit (as deter- 
mined from the 3-edge bearing method of test), and multi- 
plying the result by the load bedding factor. 


Negative Projecting Conduits 


A negative projecting conduit is one that is installed in 
undisturbed natural soil in a narrow ditch extending upward 
some distance from the top of the conduit. There is consider- 
able advantage in the use of this type of construction when 
possible, since the load under the same fill on a negative pro- 
jecting conduit is much less than that on a projecting conduit. 
For a more complete discussion of the theory and loads on 
negative projecting conduits see Negative Projecting Con- 
duits, by M. G. Spangler and W. J. Schlick, Engineering Re- 
port No. 14 (1953) of the Iowa Engineering Experiment 
Station, lowa State College. 


Imperfect Trench Conduits 


This is the term applied to a method of construction which 
decreases the backfill or embankment load on the conduit, 
thereby increasing the safe height of fill (H) that can be 
carried by the conduit. In this method of construction, the 
backfill is thoroughly compacted around and over the conduit 


PAGE 30 


TABLE 14 


Values of N for Various Classes of Bedding 


Method of Bedding Value of N 
Class A, Concrete cradle .505 
Class B, First class } .707 
Class C, Ordinary .840 


Class D, Impermissible 1.310 


TABLE 15 
Values of x for Various Projection Ratios p 
Values of x’ 


Projection ratio p Values of x 


0.0 0 ~~ Onscunan 
0.3 ye 0.217  -o74aa 
0.5 0.423 0.856 
07 0.594 inane 0.811 
0.9 0.655 0.678 
1.0 0.638 | 0.638 


to a desired height above the top of the conduit. A ditch of 
width equal to the breadth of the conduit is dug down to 
the top of the conduit and refilled with loose uncompacted 
material after which the remainder of the fill is completed 
in the normal manner. Very little data are available at the 
present time on the decrease in load transmitted to the con- 
duit by this imperfect trench method. However, the reduc- 
tion is believed to be greater than that obtained by the nega- 
tive projecting conduit method of construction. This method 
can be used to reduce the backfill load of a projecting conduit 
as well as a ditch conduit where the width of trench at the 
top of the pipe is excessive. 


Surface Loads 


In addition to the weight of the backfill material any other 
load on the surface over the conduit increases the load on 
the conduit. Table 17 gives the percentage of such loads 
transmitted to the conduit for various depths and widths of 
conduits. This table was prepared using the formula and 
methods described in “A Method of Computing Live Loads 
Transmitted to Underground Conduits” by M. G. Spangler, 
and R. L. Hennessy in Vol. 26 of Highway Research Board 
Proceedings. It will be noted that except for large conduits 
the percentage of load transmitted to the conduit in depths 
greater than 6 ft. is insignificant. Where the surface loads are 
of significant value they should be added to the backfill load 
in computing allowable height of fill over the conduit. Such 
loads are of major importance where a trench or projecting 
conduit is placed under a traffic-way with a relatively shallow 
covering of earth. 


TABLE 16* 


CALCULATED VALUES OF LOAD FACTOR FOR THE SEVERAL TYPES OF PROJECTING BEDDING 


CLASS D 


Impermissible bedding 


N=1.310 


K=0.326 


CLASS C 


Ordinary bedding 


0.840 


CLASS B 
First class bedding 
0.707 


CLASS A 


Concrete cradle bedding 


0.544 


I'sq— 0 


0.2 
(Approx.) 


0.7 
(Approx.) 


0.2 
(Approx.) 


0.7 
(Approx.) 


0.7 


re) | 0.2 | 
(Approx.) | (Approx.) 


0.2 
(Approx.) 


0.7 
(Approx.) 


Maximum 
recommended 
projection 
ratio—0.70 


Any value 


E70mest70, 


2,02 


*Compiled from tables 4, 5 and 6, pages 48, 49 and 50, Bulletin No. 112, lowa State College, February 8, 1933 by M. G. Spangler. 


2.02 


| i) 


bo 630 


2.63 


| 


PAGE 31 


Values of coefficient—C, 


Ole ae On Tee Be LD 


ae A VPP Zee 


WAL 


la 
B. 
oO 


| , 
LL Wes : 


Values of coefficient—C, 


FIGURE 12—Computation Diagram for Earth Fill Loads on Projection Embankment Conduits 


TABLE 17 


Approximate Percentage of Total Static Concentrated Surface Loads Transmitted to Conduits” 
per Foot for 3-Ft. Length of Conduit and Impact Factor of 1.0 


Outside diameter Depth of backfill above top of conduit (H,) 

of conduit | 2 4 6 8 10 

16 in 10.3 3.4 17 0.9 0.7 

30 in 16.5 6.1 3.0 1.8 1.1 

44 in 20.0 8.4 4.3 2.5 1.6 

58 in 21.7 10.1 5.4 3.3 2.1 

72 in 22.6 11.4 6.3 3.9 2.6 

100 in 23.4 12.9 7 hel f 5.0 3.5 


(1) Highway Research Board Proceedings, Vol. 26, (1946) p. 179 
Wome Ct Po 

L Fi= impact factor (assumed as 1.0 in table above may vary from 1.5 to 2.0 for 

Wp=Pressure on conduit due to surface load in Ibs./lin.ft moving loads on unsurfaced highways) (ASCE Proceedings, Vol. 73, Jan.- 


L=Length of conduit section (assumed as 3 ft. 0 in. in table above) Dec. 1947, p. 871). ‘ 
C:=Coefficient from tables by N. M. Newmark (1935)x4 P.= weight of concentrated surface load in lbs. 


PAGE 32 


CHAPTER 7 


CONSTRUCTION 


HE CONSTRUCTION of a sewer requires careful plan- 

ning and organization. This is especially true when the 
sewer traverses a busy street where prolonged traffic obstruc- 
tion would cause considerable inconvenience to the public. 
A thorough knowledge of existing conditions, careful sched- 
uling of work and skillful use of men and machines will keep 
the actual length of sewer being worked on at any one time 
at a minimum. Local conditions influence the method of 
construction. Type and nature of the soil and ground water 
conditions determine whether sheeting is necessary. Obstruc- 
tions in the line of the sewer or traffic conditions may make 
the use of tunnels or jacking of pipe desirable. 


Excavation 
Open Cut 


Machine methods for excavating sewer trenches are much 
more economical than hand methods. Every effort should be 
made therefore to locate the line of construction which will 
permit the maximum use of excavating equipment. 


SHEETING AND BRACING. In open-cut excavation, 
whether by machine or hand, precautions should be taken 
to prevent caving during construction which might result in 
injury or loss of life. In hard, firm soils a minimum of sheet- 
ing and bracing may prove sufficient. Some soils which re- 
quire little bracing when dry may prove difficult when wet 
and require extensive sheeting and bracing. The require- 
ments for sheeting and bracing of the Corps of Engineers, 
United States Army, as outlined in a manual, Safety Require- 
ments for Excavation, Building and Construction, revised 
March 15, 1943, by the Safety and Accident Prevention 
Branch of the Construction Division, are as follows: 


“Excavation 


“A. The sides of excavation 5 ft. or more in depth shall be 
supported by substantial and adequate sheeting, sheet piling, 
bracing, shoring, etc., or the sides sloped to the angle of re- 
pose. Substantial and adequate sheeting, sheet piling, bracing, 
shoring, etc. shall be based upon calculations of pressures 
exerted by and the condition of the materials to be retained. 

“B. Foundations, adjacent to where excavation is to be 
made below the depth of the foundation, shall be supported 


by shoring, bracing, or underpinning as long as the excava- 
tion shall remain open. 

“C. Excavated or other material shall not be stored 
nearer than 2 ft. from the edge of the excavation. 

“D. Bridges or walkways with guard rails shall be pro- 
vided where men or equipment must cross over trenches, 
ditches, etc. A temporary guard railing or other effective 
guard or barricade shall be provided at or near the edge of 
an excavation as soon as possible, except where the installa- 
tion of such safeguard will interfere with the excavation or 
other work. 

“E. Red lights or torches, maintained from sunset to 
sunup, shall be placed on excavation barricades and along 
the sides of unbarricaded excavations which are exposed to 
paths, walkways, sidewalks, driveways, or thoroughfares. 

“F, Materials used for sheeting and sheet piling, brac- 
ing, shoring, and underpinning, shall be in good serviceable 
condition and timbers used shall be sound, free from large or 
loose knots, and of the required dimensions. The material 
specifications are the minimum requirements and the spac- 
ing of material members is the maximum allowable in se- 
curing trenches against slips, cave-ins, and slides. Where con- 
ditions are encountered which require materials of greater 
strength or closer spacing of timbers to hold the soils se- 
curely in place, the sizes of timbers in such cases shall be in- 
creased to compensate for the overload. 


“Trench Excavation 


“A. The following provision for shoring and bracing of 
trenches shall not apply where solid rock, hard slag, or hard 
shale is encountered or in which employes are not required 
to be or to work. 

“B. The sides of trenches in material, other than those 
listed in paragraph F, which are 5 ft. or more in depth and 
8 ft. or more in length shall be securely held by shoring and 
bracing, or sloped to the angle of repose of the materials 
being excavated. 

“C. If the unit tunnel method is used, the length of 
earth left in place between the separate unit trenches shall 
be not less than one-half the depth of the trench and shall 
be considered as taking the place of shoring and bracing. 


PAGE 33 


“D. Whenever or wherever the unit tunnel method is 
used and where there is apparent danger of slips, slides, or 
cave-ins, trenches or tunnels in which men are employed 
shall be shored and braced or otherwise retained as may be 
necessary to prevent caving. 

“E. Trenches over 8 ft. in length and 5 ft. or more in 
depth in hard compact material, shall be braced at intervals 
not exceeding 8 ft., with 2-in. by 6-in. planks, or heavier ma- 
terial, placed vertically in the trench opposite each other, 
backed up by 2-in. by 10-in. planks bearing against the walls 
at the same intervals as cross braces, struts, or trench jacks. 
These braces shall, if possible, extend to the bottom of the 
trench and be supported by horizontal cross braces or struts. 
Bracing and shoring of trenches shall be carried along with 
the excavation and must in no case be omitted, except where 
a mechanical digger is used, the shoring shall be placed with- 
in 6 ft. of the lower end of the boom. Undercutting shall not 
exceed 6 in. on either side of the trench. 

“E In partly saturated, filled or unstable soils or where 
running material is encountered, such as quicksand, loose 
gravel, loose shale, or completely saturated material, the 
sides of the trenches 4 ft. or more in depth shall be secured 
by the use of continuous vertical sheet piling and suitable 
braces. In trenches over 4 ft. in depth wooden sheet piling 
shall not be less than 2 in. in thickness. 


Open-type sheeting on southwest side interceptor sewer of the Sanitary 
District of Chicago constructed in 1947. Note width of trench offset in 
lower 15 ft. of a 35-ft. cut. 


“G. Sheet piling shall be held in place by longitudinal 
beams at vertical intervals of 4 ft. The longitudinal beams 
shall in turn be supported by the cross braces or struts spaced 
a maximum of 4 ft. The longitudinal beams shall be in no 
case less in strength than that of a 4- by 4-in. beam; and when 
the longitudinal distance between cross braces or struts ex- 
ceeds 4 ft. and less than 6 ft., the longitudinal beam shall be 
not less than a 4- by 6-in. beam. 

“H. Vertical braces and longitudinal beams in trenches 
shall be supported by horizontal cross braces or struts, screw 
jacks, or timber placed at right angles to both braces, cleated 
and rigidly screwed or wedged. The timbers or struts shall 
be not less in strength than the following trade sizes: 


Size of Cross 


Width of Trench Braces or Struts 


lettiatonouiie 4x4 in. 
SalttOnOntte 4x6 in. 
Clit atoroutts 6x6 in. 


“I. One horizontal cross brace or strut shall be required 
for each 4 ft. of depth or major fraction thereof. 

“J. In case it is desired to increase the vertical spacing 
between longitudinal beams or cross struts, the longitudinal 
beams, cross struts, and vertical sheet piling shall be increased 
in size to compensate for the overload. 


Solid sheeting between H-beams on South Capitol St. stormwater sewer 
in Washington, D.C. constructed in 1943. Note piles and gravel base in 
place in foreground and concrete invert in background. 


“K. Additional precautions by way of shoring and brac- 
ing shall be taken to prevent slides, or cave-ins, when exca- 
vations or trenches are made in locations adjacent to back- 
filled excavations or subjected to vibrations from railroad or 
highway traffic, the operation of machinery, or any other 
source. 

“L. Ladders, extending from the floor of trench exca- 
vation to not less than 3 ft. above the top ground surface, 
shall be placed in the trench excavation at 50-ft. intervals to 
be used as a means of entrance and exit therefrom.” 

In deep cuts care must be taken to avoid excessive back- 
fill loads on the sewer structure. Since the backfill load varies 
directly as the square of the width of the trench at the top 
of the sewer structure, the width of the trench at this level 
should be kept to a minimum. This may be accomplished by 
off-setting the sheeting near the top of the conduit as shown 
in Fig. 13. 


Tunnel Excavation 


In some instances the use of tunnel construction may be 
more practical than an open trench. For example, in closely 
builtup areas trench construction may interfere with travel 
or business or endanger building foundations. Where the 
sewer is very deep, tunneling also may be more economical 
than open cut. 

Tunnel construction introduces hazards not normally 
encountered in an open ditch. Such problems as ventilation, 
lighting, falling rock and cramped working space compli- 
cate this type of construction. 

The soil through which the sewer must pass influences 
the construction procedure. Very wet soils make tunneling 
difficult and hazardous so that compressed air must be used 
to prevent seepage and caving prior to timbering. Only in 
solid rock can a tunnel be excavated without timbering. 

In pipe sewer construction the tunnel excavation is 
completed before the pipe are installed. Then the pipe are 
carried into place either on a special cart or by sliding them 
over skids. The pipe should be blocked to proper line and 
grade before the joint is constructed. Lean concrete is placed 
in the space between the pipe and the wall of the tunnel. 
When cast-in-place concrete sewers are constructed in tun- 
nel the concrete walls of the sewer may be placed closely be- 
hind the tunnel excavation, or the concrete lining may be 
delayed until all excavation is complete. Fig. 14 illustrates 
several types of tunnel timbering. 


Pipe Sewers 
Trench Width 


The trench at the top of a pipe sewer should be only of suffi- 
cient width to permit the proper bedding and placing of the 
pipe and the construction of the joints. Some authorities 
recommend that this distance be kept to within four-thirds of 
the internal diameter of the pipe plus 8 in. Tables 6 to 9 on 
pages 26 and 27 give permissible depths of backfill on con- 
duits for width of trench equal to the external diameter of 
the pipe plus 16 in. for pipe up to 33-in. internal diameter, 


and the external diameter of the pipe plus 24 in. for all con- 
duits over 33-in. internal diameter. 


Embedment and Backfill 

Proper embedment of concrete pipe cannot be overempha- 
sized. The importance of bedding for increasing the struc- 
tural capacity of a pipe is evident from tables 6 to 9, page 
26, which show the permissible depth of fill for various 
classes of embedment. Regardless of the method of embed- 
ment, where bell and spigot pipe are used, holes should be 
dug for each bell. 

In rock, shale, hard clay, etc. the excavation should be 
carried at least 8 in. below grade for cuts up to 16 ft., and 
14 in. more for each additional foot of cut. This excavation 
should be replaced with fill material which will provide a 
firm but slightly yielding support for the pipe. 

Where unstable soil is encountered at the bottom of 
the trench it may be necessary to provide additional support 
to prevent settlement or disalignment. In such instances, con- 
crete cradles, piles or other suitable foundation of granular 
materials such as crushed stone or gravel should be provided. 

After the pipe have been properly embedded the re- 
mainder of the backfill material may be placed. Care should 
be taken to keep tractors, bulldozers and other heavy equip- 
ment from traveling over the pipe until the backfill has been 
carried to a height above the top of pipe sufficient to prevent 
excessive load on the sewer structure. (Table 17, page 32 
gives the percentage of such loads carried to the pipe struc- 
ture for various widths and depth of trench.) This backfill 
material should be placed in uniform layers and if the sewer 
is under a street or other location where settlement would 
be objectionable it should be compacted in 6-in. layers. In 
cases where pavements are to be placed over the sewer trench 
within a year, sand or other granular backfill material should 
be used. 


Removal of Water 
Water in the trench must be removed to insure proper place- 
ment of the pipe and construction of the joints. This may 
be done by direct pumping from drainage sumps or by low- 
ering the groundwater level through the use of wellpoints. 
WELLPOINTS. In permeable soils wellpoints have been 
particularly effective in lowering the groundwater level to 
permit dry construction methods, thus eliminating the need 
for sheeting in some cases. A single line or stage of well- 
points may be capable of lowering the groundwater level 
15 to 20 ft. Where impervious layers of soil are encountered, 
a line on each side of the trench may be necessary. 
Wellpoints are usually 2 in. to 3 in. in diameter and 
are connected to 6- or 8-in. header pipes at multiples of 214 
ft. They are placed by jetting or drilling. Each wellpoint 
should be provided with a valved, swing joint connection to 
the header. The valve permits regulation of the amount of 
water entering the header pipe from each individual well- 
point so that uniform flow can be maintained during pump- 
ing. The swing joint connection permits the location of the 
wellpoint to be varied slightly from the connector spacing 


PAGE 35 


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4 
{7 
y v, 
fy i 
j , 
4 
aos 
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Lf 
oA 


wt 


YR, of ee we 
EG sa 
EE NN 7) fp : 


SHEETING 
TWO LENGTHS 


SHEETING 
ONE LENGTH 


aS 
BEI g 


‘EN 


*, ~ 4, 


nch Sheeting 


FIGURE 13 —Typical Tre 


PAGE 36 


Spreader 


Knee braces 
Spreader 


Box TYPE 


Crown plank 


Haunch piece 


Leg 


Spreader 


Sill 


ARCHED TYPE 


Wedge 
Sleepers Poling boards Blocking 
SS SS ow L > & L % > SIS 
aw oe PILLS ork Z Xe, 
2 8) e —w_ 
__. ESS ey a el a 
es fe Od Os F< 
Sass 
=) | ee a) a 
(a | | eee 
oe | a e/a Stays 
— Ef ay fe 
EE a |: Face 
| noe eee) Weern| Paani Ke Se boards 
=l\ | i ees > ee eee ee: 
OTRO BSS TSO ASOT STEVI RS TRO RSI FIST = > 6 
Frames Needle beam Needle 


LONGITUDINAL SECTION 


POLING BOARD TYPE 


FIGURE 14—Typical Tunnel Bracing 


Leg 


Cap & LEG TYPE 


Crown plank 


Set pieces 


Stringer 


Cross brace 


Foot block 


Side poling boards 
Spacers 


a= 
i 
I 
kk 

a 
Ik 


5 
Ny 
a 
4 
a 
4 
a 
4 


TRANSVERSE SECTION 


PAGE 37 


A typical installation of wellpoints, showing pump, header, valves and 
swing joint connections. 


on the header pipe. Valves are generally placed at intervals 
of 150 to 200 ft. in the header line. Normally 450 to 600 ft. 
of header pipe is required to insure continuous operation as 
the work progresses. Under normal conditions, two pumps 
are required. One is connected to the header and the other is 
used for jetting wellpoints. 

The location, number, spacing and length of wellpoints 
together with the size and number of pumps required are 
dependent upon the nature of the soil and the volume of 
water encountered. This can only be ascertained through ex- 
perience or trial. The photograph above shows a typical in- 
stallation of wellpoints which eliminated the use of sheeting 
and permitted fast and efficient construction of the project. 


Pipe Laying 


Pipe laying is an important part of the sewer construction 
and often receives too little supervision or inspection. Each 
length of pipe should be checked for cracks and defects be- 
fore placing in the line. Each pipe should be placed carefully 
to line and grade and in close contact with adjoining pipe. 
The bell end of a bell-and-spigot pipe and the groove end of 
a tongue-and-groove pipe are laid upstream. Various methods 
are used for drawing the pipe tightly together. Small pipe 
usually are pushed together by means of a crowbar or pry. 
For larger-sized pipe a winch can be used. In this case a 
timber slightly longer than the diameter of the sewer can 
be placed some distance back in the portion of the sewer 
already laid. The winch is then anchored to this timber while 


PAGE 38 


Laying 84-in. reinforced concrete pipe for drainage of Calumet Express- 
way in Cook County, Ill. in October 1948. Pipe sizes on this project 
ranged from 12 in. to 96 in. in diameter. 


a cable attached to the winch is fastened to the pipe to be in- 
stalled. 


Pipe Jointing 

Pipe jointing should receive particular attention as good 
joints add to the watertightness of the sewer. Appreciable 
infiltration of groundwater may carry soil particles into the 
sewer and cause undermining, with subsequent settlement 
of not only the sewer but of roadways or buildings on or 
adjacent to the sewer. Infiltration in sanitary sewers may 
cause overloading of the sewer and treatment works. 

Joints in concrete sewers can be placed in two general 
classifications: (1) rigid joints such as neat cement, cement 
mortar and cement grout and (2) flexible joints, such as 
bituminous materials and rubber. Sometimes a combination 
of these materials is used. A good joint material should be 
durable, watertight and resistant to root penetration. It should 
bond well with the pipe and in some instances have slight 
flexibility. 

Flexible joints are used where unstable ground condi- 
tions are encountered. However, even with the most elastic 
joint material there is a limit to the amount of displacement 
a pipe line will withstand without affecting its hydraulic 
properties or its structural capacity. In unstable soils it is 
always better to stabilize the sewer line by the use of cradles, 
piles or granular materials rather than to rely on a flexible 
joint to hold the sewer pipe together. 


Cement Joints 


Cement-type joints are the most commonly used for jointing 
concrete pipe. When properly made they are watertight, re- 
sistant to root penetration and durable. When pipe lines are 
constructed on unstable foundations the rigidity of this type 
of joint might be objectionable. 

NEAT CEMENT JOINTS. Joints of neat portland cement 
paste made with about 1 to 114 gal. water per sack of cement 
have been used for a number of years for calking cast-iron 


water pipe in many cities in this country. Ic 
has also been used for calking bell-and- 
spigot sewer pipe. 

Portland cement mixed with enough 
water to make a soupy consistency has been 
used as a grout for sealing joints in concrete 
pipe. Forms or molds are used to retain the 
grout during placing and hardening. It is 
easy to handle but because of its high water 
content is likely to develop shrinkage cracks 
during hardening. 


CEMENT MORTAR JOINTS. Grout 
made with a mixture of 1 part portland 
cement to 2 parts sand and 61 to 7 gal. of 
water per sack of cement makes a satisfac- 
tory material for sealing joints. The grout 
usually is poured or pumped into the joint 
space being retained by molds or runners 
around the pipe. Cement mortar of a stiffer 
consistency may be used for the lower and upper portions of 
this joint, and may be used for the entire joint as follows: 

(1) In laying bell-and-spigot pipe, joint ends should be 

well cleaned and thoroughly soaked with water before 

the joint is made. Stiff mortar is then placed in the lower 

portion of the bell end of the pipe already laid. The 

spigot end of the next pipe after coating the top portion 

with mortar is then inserted into the bell of the first-laid 

pipe. Care should be taken to see that the inner surfaces 

of the abutting sections are flush and even. The annular 

space remaining in the joint is then filled with cement 


mortar. All mortar on the inside of the pipe is then wiped 
clean. 


(2) In laying tongue-and-groove pipe, a shallow excava- 

tion is made underneath the pipe at the groove end. This 

space is filled with mortar. The tongue-and-groove ends 

of the pipe also should be well cleaned and thoroughly 

soaked with water just before the joint is made. Cement 

mortar is then applied to the lower portion of the groove 

end of the pipe already laid and to the upper portion of 

the tongue of the pipe being laid. The tongue end is then 

inserted in the groove end of the first pipe until mortar 

is squeezed out on the interior and exterior surfaces. The 

remaining annular space is then filled with mortar. The 

interior surface of the pipe is then cleaned of all ex- 

truding mortar. 
Some engineers require that for bell-and-spigot pipe the 
spigot end be centered in the bell end by means of a packing 
gasket of twisted oakum or hemp of proper thickness and 
sufficient length to pass around the pipe and lap at the top. 
After the pipe has been properly placed and bedded to line 
and grade this gasket is calked into the annular space and 
the remainder of the space filled with cement mortar. The 
oakum or hemp gasket may be impregnated in neat cement 


grout before using or can be placed dry as desired. 


MACHINE GROUTED JOINTS. Equipment has re- 
cently been developed for placing portland cement mortar 
grout in joints by a pneumatic process. The equipment used 
is similar to that used in shotcreting except that (1) the 
nozzle of the gun is smaller, usually about 7@ in.; (2) the 
Operating pressure is only about 25 psi and (3) the mixing 


Jointing concrete pipe sewers in Oklahoma City by pneumatic process in 1949. 


of the mortar is accomplished by means of air jets. This 
equipment has been used quite extensively in sewer projects 
in Oklahoma City; Union Gap, Spokane and Seattle, Wash.; 
Junction City and Hood River, Ore.; Great Falls, Mont.; 
Coachella, Calif. and in many other localities. It is reported 
that if ordinary care is taken, machine-grouted joints are 
more watertight than hand-mortared connections. 


CEMENT MORTAR BANDS. Bands of portland cement 
mortar are often specified around the exterior of the pipe 
at a joint. They are usually about 5 in. or more in width and 
not less than 1 in. in thickness for the smaller-size pipe, in- 
creasing in thickness somewhat as the pipe increases. The 
external surface of the pipe should be thoroughly cleaned 
and wetted just before the band is placed. The consistency 
of the cement mortar should be slightly stiffer than that re- 
quired for the joint. As the mortar band is brought up from 
the bottom around the outside of the pipe on either side, 
backfill material can be placed against it to prevent slough- 
ing of the mortar. In lieu of this, a strip of cheesecloth may 
be placed under the pipe and the ends brought up around 
and over the pipe as the mortar band is placed. 


Bituminous Joints 


Bituminous joints consist of a tar or asphalt to which an 
organic filler is sometimes added. Some of these can be 
applied cold, others must be heated and poured into the 
joint space by means of a runner placed around the pipe. 
One proprietary type permits precasting bituminous rings 
on the bell-and-spigot ends of the pipe. An adhesive solvent 
is then painted on these rings immediately before the pipe 
is assembled which bonds the two parts of the joint together. 
The principal objection to bituminous joints is their lack of 
resistance to root penetration. In one series of tests* it was 


*Harvey W. House and Richard Pomeroy, “Sewer Pipe Jointing 
Research—A Progress Report”, Sewage Works Journal, Vol. XIX, 
No. 2 (March 1947), page 191. 


PAGE 39 


reported that coal tars having a high adhesion and a low 
penetration showed promise of being more resistant to root 
penetration than did the other asphalt and resins tested. 


Rubber Joints 


Rubber gaskets backed up with cement mortar have an 
excellent record for durability and watertightness as a joint 
material. It is maintained that rubber under compression will 
not deteriorate with age to any great extent. While rubber 
gaskets have not been in use for many years as a jointing 
material for sewers, they have been used successfully for more 
than 50 years for sealing cast-iron gas and water mains. One 
type of rubber gasket consists of a ribbed band which is 
cemented on the tongue or spigot end of the concrete pipe 
by the manufacturer. As the tongue or spigot end is inserted 
into the groove or bell end of the adjoining pipe, the ribs 
are rolled over and compressed to make a tight seal. The 
remainder of the annular space is then filled with a cement 
mortar or cement grout. Another type consists of a solid 
rubber ring which is slipped on the tongue or spigot end of 
the pipe just before it is inserted into the groove or bell dur- 
ing laying. The ring is compressed as the pipe is “shoved 
home”, and the remainder of the joint is then filled with 
cement grout or mortar. Rubber joints backed up with ce- 
ment or mortar have a satisfactory record. 


Asphalt Latex Joints 


There are proprietary materials on the market composed of 
mixtures of latex, asphaltic oil and other ingredients which 
promise to be satisfactory jointing material for sewers. 


Jacking Concrete Pipe 


Occasionally a sewer must be installed beneath a highway or 
railroad without interrupting traffic. This may be done by 
tunneling or by jacking concrete pipe beneath the roadway. 

In jacking, the pipe are pushed beneath the roadway 
by hand-operated hydraulic jacks. Reinforced concrete pipe 
are of sufficient strength that they can be used for this pur- 
pose. Concrete pipe of the tongue-and-groove type from 
30-in. to 96-in. diameter have been successfully installed by 
this method. Pipe less than 30-in. diameter are so small that 
men cannot work in them efficiently. Pipe greater than 96-in. 
diameter require such powerful jacks and heavy timbering 
frames that they are not generally economical. 

To begin the operation, a working pit is excavated at 
the point of beginning. This pit should be large enough to 
provide space for one or two sections of pipe, frames to sup- 
port them, jacks and the backstop. Guide timbers for the 
support of the pipe are very carefully installed so that the 
pipe will be at the correct line and grade. With large pipe 
the inner edges of these timbers can be protected with angle 
irons. A steel cutting ring may be installed on the leading 
edge of the first pipe. A jacking head, consisting of bearing 
blocks usually of oak, is used to transfer the pressure uni- 
formly from the jacks to the pipe. The number of jacks re- 


PAGE 40 


Typical jacking layout, showing pit, jacking head, and jacks used in 
jacking concrete pipe under B&O tracks in Cincinnati. 


quired depends upon their capacity, the pipe size, the nature 
of soil and the length of pipeline to be installed. The jacks 
must have a support at the rear of the jacking pit substantial 
enough to withstand the thrust which will be developed 
during jacking. Ingenious schemes have been developed to 
provide suitable backstops or thrust blocks. Timbers, con- 
crete bulkhead, and in some cases the exposed end of the 
completed sewer have been utilized for this purpose. A typi- 
cal jacking layout is shown in Fig. 15. 

As the pipe progresses, workmen excavate the material 
from the head of the pipe. Excavating is expedited in hard 
ground by the use of mechanical spades. Usually the exca- 
vation is about 1 in. larger than the pipe at the top and sides. 
When the operation has progressed a few feet, a cart or sled 
may be used to remove the excavated material. In some in- 


Hydraulic jack 
Backstop 
Thrust blocks 


| Bed ages 
: PAX) 7 

nh eee SRS Odea? 

(7; eee ae 
. ATI Noes CISTI 


Sie 


Guide toners 
Anchor cables 
Deadman 


FIGURE 15—Typical Jacking Layout 


Left—Jacking 96-in. reinforced concrete pipe under Erie Railroad at Tonawanda, N.Y. in 1949. Note 20-ft. portable belt conveyor used to remove 
excavated material. Right—Casting a 100-ft. section of 12-ft. internal diameter concrete pipe at Long Beach for Los Angeles subaqueous outfall sewer 
in 1947. This pipe was floated by means of pontoons to Santa Monica Bay where it was sunk in place and is now serving the Hyperion Sewage 
Treatment Works. 


stances mechanically operated belt conveyors have been used 
for this purpose. Jacking is usually done upgrade so that 
seepage will drain to the working pit which may be kept 
dry by the use of wellpoints or by a sump pump. As the work 
progresses the line and grade of the lead pipe should fre- 
quently be checked so that corrections can be made before 
large errors occur. 

It is important to keep the pipe moving as much as 
possible. When a long stop is made there is danger that the 
soil will take a set around the pipe thus freezing it and 
making it difficult, if not impossible, to get it started again. 
It is therefore advisable when jacking is once started to con- 
tinue day and night until completed. If, however, the work 
is stopped for any reason, arrangements should be made to 
occasionally move the pipes slightly to prevent freezing. If 
for any reason it becomes impossible to move the pipe during 
jacking, the operation may be completed from the other side 
of the roadway. 


Subaqueous Sewers 


In order to eliminate or reduce pollution of recreational 
beaches some coastal communities have extended outfall 
sewers a considerable distance offshore. This type of con- 
struction is highly specialized and costly since underwater 
installation of sewers is difficult and hazardous. 

Recent notable examples of this type of construction 
are the outfall sewers of the sewage works for Toronto- 
Ashbridge Bay, Canada, and the Hyperion Sewage Works of 
Los Angeles. The former consists of pipe 60 in. in diameter 
extending 5330 ft. into Lake Ontario and is submerged a 
depth of 19 ft. at the outlet end. The latter consists of pipe 


12 ft. in diameter by 100 ft. long, extending 1 mile into the 
Pacific Ocean and is submerged 50 ft. at the outlet. 

Since these sewers are built expressly for the purpose 
of discharging treated sewage as far from shore as possible 
considerable care is taken to construct watertight joints. In 
the Los Angeles sewer, specially designed joints with steel 
rings to aid in aligning the pipe and to prevent spalling of 
the concrete were provided. Each joint was provided with 
a rubber collar. The pipe were supported on concrete caps 
constructed on piles to prevent settling. 


Cast-in-Place Sewers 


Cast-in-place concrete sewers should be designed so that the 
bearing value of the foundation support will not be ex- 
ceeded. This may require the use of special subbase materials 
such as crushed stone or gravel and in extreme cases the use 
of piles. 

In cast-in-place sewers the bottom of the trench is usu- 
ally shaped to conform to the exterior surface of the sewer 
for some distance above the invert. At that point on each 
side of the sewer a longitudinal joint of the tongue-and- 
groove type is provided. This joint may or may not include 
a metal or rubber waterstop to insure watertightness of the 
joint. The concrete is deposited by means of spouts, elephant 
trunks, buckets or pumping equipment. The invert of the 
sewer is screeded to line and grade by means of a templet 
cut to the shape of the sewer invert. Forms are provided on 
the inside of the sewer above the longitudinal joint on each 
side of the invert and may be required on the outside for 
some distance above the longitudinal joint. Concrete is usu- 
ally consolidated by hand spading or by vibration. 


Left—Placing concrete by means of a spout and hopper on double reinforced concrete box sewer in Lexington, Ky. Right—Placing concrete by means 
of a bucket and crane, for 15x10-ft. rectangular reinforced concrete box sewer on Bloody Run Contract No. 1, at Cincinnati in 1947. 


CHAPTER 8 


SEWER APPURTENANCES 


HE VALUE of a sewer is measured by the service it 
gives, but to give this service certain appurtenant struc- 
tures are necessary. These structures provide inlets and out- 
lets for sanitary sewage and storm drainage. They provide 
for the junction of two or more sewers without excessive 
disturbance of the flow and are a means of entry for inspec- 


tion and maintenance of the sewer. 


MANHOLES. The most common appurtenance to a sewer 
is the manhole which permits the entry of men and equip- 
ment for inspection and maintenance. Manholes should be 
placed at every change of grade or direction of the sewer. 
For small-sized sewers they should be spaced at intervals of 
not more than 300 to 400 ft. on tangents; for larger sewers 
which are readily accessible to workmen, they may be spaced 
at greater intervals. 

Concrete is well suited to manhole construction because 
of its strength, adaptability and watertightness. Cast-in-place 
concrete, concrete brick, concrete block or precast concrete 
pipe are used in making manholes. Fig. 16 illustrates several 
kinds of concrete manholes. A channel having a capacity 
equal to that of the incoming sewer is constructed in the 
floor or bottom of the manhole. The remainder of the floor 
of the manhole should slope toward this channel. The floor 
is usually built of cast-in-place concrete. However, precast 
concrete sections have been used. Manholes should be at least 
4 ft. in diameter to provide ample space for operation of 
cleaning equipment with top opening about 24 in. in diam- 
eter, large enough to admit a man. The top of the manhole 


Precast concrete manhole constructed on 24-in. concrete pipe sanitary 
sewer in Mandan, N.D. in 1946. Sixty-inch concrete pipe stormwater 
sewer shown on left. 


Precast segmental concrete block manhole constructed on Tri-State High 
way, Cook County, Ill. in 1948. 


is usually provided with a cast-iron or concrete frame, which 
supports a perforated cover. Heavily galvanized or othe: 
noncorrosive ladder rungs are attached to the manhole wal 
on 15- to 18-in. centers. These rungs are usually precast unit: 
embedded in the wall or they may be assembled on a frame 
as a ladder and fastened to the wall of the structure. Or 
large sewers the manhole may be constructed to one side 
This permits easier access to the sewer than if entrance i 
made at the crown. 


DROP MANHOLES. (See Fig. 16) Drop manholes shoul 
be constructed where there is an appreciable drop in elevatiot 


Frame 


Ring 


One piece 
reinf.conc. 


taper section ———— 
JN SSN 


Reinf. conc. 
pipe sections 
of variable 
heights 


Cast-in-place 
concrete berm 


Cast-in-pl 
and bottom ph 


concrete berm} 


eee ome on ae 
EO OO” : ; ; 2 
Sewer line Sewer line Sewer line 
SECTION OF SECTION OF SECTION OF 
CONCRETE PipE MANHOLE CONCRETE BLock MANHOLE CAST-IN- PLACE MANHOLE 


Cover 
im oe 


Concrete pipe, LO ———— = I 

concrete block fal eee ee at, 
or cast-in-place 
concrete 


Spring line 


Cast-in-place 
conc. berm 
and bottom 


Cast-in-place 
concrete bottom 


Sewer line 


SECTION OF SECTION OF 
DROP MANHOLE LARGE SEWER MANHOLE 


FIGURE 16—Types of Manholes 


in a sewer line or between intersecting sewer lines. Such LAMPHOLES. Lampholes are 6- to 10-in. openings or 
construction reduces turbulence and prevents sewage from shafts constructed from the ground surface to the sewer 
splashing on men working within the manhole. through which a light may be lowered for sewer inspection, 


PAGE 43 


ae 


Left—Cast-in-place concrete manhole constructed on 42-in. sewer near Lincoln Blvd., Oklahoma City in 1948. Right—Concrete inlet with side entrance, 


or a hose for flushing. They also serve as vents. They are 
a poor substitute for manholes but may be justified between 
manholes in large sewers or where sewers are placed at 
great depths. Concrete pipe are particularly well adapted for 
construction of lampholes. 


INLETS. One of the necessary appurtenances to a storm 
sewer system is the inlet through which storm water enters. 
Inlets are located at street intersections and at intermediate 
points between intersections. At intersections, inlets should 
be placed so that they will intercept storm runoff before it 
flows across the path of pedestrians or across the street. Be- 
tween intersections the location of the inlets is determined 
by the grade of the street and height of curb. Inlets should be 
connected to catch basins and not directly to the sewer. This 
is especially true for combined sewers as inlets ordinarily 
are not provided with traps as are catch basins. Inlets may 


ied os 


y ; 0 
| (e207 | 
D 


iameter 


== 


= 8" 


A" to 2’ 


3-0" to 4:0" 


Variable 


Precast or 
cast-in-place 
concrete 


Concrete pipe, 
concrete block, 
or Cast-in-place 
concrete 


be constructed of cast-in-place concrete or precast concrete 
units. A concrete or cast-iron grating is provided for the top 
or side of the inlet. 


CATCH BASINS. Catch basins are inlets in which a stor- 
age space is provided in the bottom for the settlement of 
suspended solids which might otherwise be deposited in the 
sewer. Catch basins are usually provided with a trap to pre- 
vent sewer odors reaching the street. They are generally 
3 to 4 ft. in diameter and 4 to 6 ft. deep. Catch basins may 
be of cast-in-place concrete, precast concrete brick, block or 
pipe or the entire catch basin may be a precast unit. A per- 
forated lid 20 to 24 in. in diameter of metal or concrete is 
provided for the top. 


FLUSH TANKS. In flat areas, portions of the sewer are 
sometimes constructed on slopes which will not produce 
self-cleaning velocities. This makes it necessary to flush these 


Variable 


1%" Sand cushion 


FIGURE 17—Types of Catch Basins 


PAGE 44 


sortions occasionally to remove any deposited solids. 
fn some cases, automatic flush tanks are provided 
it the upper ends of such sections. These devices 
sradually fill with water until a certain level is 
ached at which time the tank empties suddenly 
causing a rush of water down the sewer. Flush 
anks which introduce the possibility of a cross 
connection between the public water supply and 
the sewage are undesirable because of the danger 
of pollution of the public water supply. 


PUMPING STATIONS. In some areas lift sta- 
tions may be desirable in lieu of deep cuts otherwise 
necessary for gravity flow. Such stations should be 
avoided whenever possible because constant care 
and maintenance are required for their operation. 
If necessary, pumps and motors should be installed 
in a dry well where the operator will have access 
for inspection and maintenance. Duplicate pumps 
each having a capacity somewhat greater than the 
average flow are desirable. The floor of the pit in 
which the sewage is collected, called the wet well, 
should be sloped toward the pump suction lines. 
The wet well should be amply ventilated. The dry 
well should be insulated from the wet well to pre- 
vent any gases from entering. Pumping stations usu- 
ally are constructed of cast-in-place concrete. 


SIPHONS. Sewers are carried under streams or 
other obstructions by depressed sections known as 
inverted siphons. Because of the sag caused by 
depressing the sewer, the velocity of the sewage 
through the siphon should be somewhat greater 
than the self-cleaning velocities provided for sewers. 
Two lines of concrete pipe of unequal size are usually pro- 
vided. The smaller is designed and placed to carry minimum 
flows at a velocity of 2 to 3 fps for sanitary sewers, and from 
3 to 4 fps for storm or combined sewers. If velocities suffi- 
cient for self-cleaning cannot be obtained by the slope avail- 
able, pumping or some other means must be employed to 
increase the velocity. 


DIVERSION CHAMBERS. These may be simple over- 
flow by-passes formed by low dams or deflector plates, or 
they may be complex, gated structures operated electrically 
by remote control and enclosed in a concrete structure. In 
case the sewer makes a turn in the chamber, a low dam is 


used to conduct the dry-weather flow around the turn. 


1 


Storm flows overtop the dam and are then by-passed directly 
to an outlet stream. Deflector plates permit the dry-weather 


flow to pass unmolested beneath them but deflect storm 


flows to a by-pass which empties into an outlet stream. 


Junction chamber on 4th St. stormwater sewer, Washington, D.C. 


Gated structures permit diversion of all or any part of the 
flow in the sewer. The condition of the outlet stream will 
determine the amount of sewage which can be safely dis- 
charged into it. 


JUNCTION CHAMBERS. These are concrete structures 
constructed at the intersection of two or more large sewers. 
Unless these structures are designed properly the converging 
of two or more streams of sewage will be accompanied by 
excessive turbulence and loss of head. This may cause the 
release of hydrogen sulfide gas, the settlement of suspended 
matter, or the overloading of one or more of the branch 
sewers with a resultant flooding of basements. Therefore, 
junction chambers should be designed so that there is a 
minimum of interference in the convergency of two or 
more sewer lines. This requires a careful study of conditions 
at each junction chamber, a knowledge of the principles of 
hydraulics and experience in such design. 


PAGE 45 


CHAPTER 9 


— = 


MAINTENANCE AND REPAIR a 


DEQUATE AND REGULAR INSPECTION of the 

sewer system is an essential requirement for economical 
and efficient operation. Buildings, pavements, and other 
municipal improvements above ground are seen daily and 
receive maintenance and repair as needed. Sewers, buried 
during construction, are usually forgotten until failures occur. 
These failures can be foreseen by periodic inspection and 
avoided by prompt maintenance. 


Causes of Failures and Repair Methods 


Failures caused by stoppage are usually the result of (1) root 
growth through joints into the sewer; (2) settlement of the 
sewer lines due to unstable subgrade or improper embed- 
ment; (3) sewer slope insufficient to provide velocities which 
are self-cleaning and (4) failure of the sewer structure. 


Root Growth 


Root penetration through sewer joints is perhaps the most 
frequent cause of stoppage. Equipment varying from hand- 
operated jointed rod cutters to power-driven machines are 
used to remove the root growths. Some cities* have found 
that root growth may be inhibited by periodically dropping 
blue vitriol crystals into the sewer above the root growth. 
The amount to be used in any area should be determined 
by qualified engineers or chemists. 


Deposition of Solids 


Deposition of solids in sewers because of sags in sewer 
lines or flat grades can be removed either by periodic flushing 
or by mechanical cleaning. Cleaning equipment varies from 
small portable water tanks to highly mechanized equipment. 
When flushing will not remove the solids, sand buckets or 
scoops attached to cables may be pulled through the sewer 
by mechanical means. A cleaner which has a water-powered 
rotating cutter will be found quite effective in removing ex- 
tremely large deposits. For sewers 6 to 36 in. in diameter, 


*John W. Hood, “How Copper Sulfate is Used for Root Control in 
Sewers”, Public Works, (1949) page 63. 


PAGE 46 


rubber balls approximately the size of the sewer have been 
found effective in cleaning sewers. The ball is propelled 
through the sewer by hydraulic pressure built up behind it 


Structural Failure 


Structural failure of a sewer may result from a number of 
causes. Among these are improper design or construction, 
lack of maintenance, unanticipated loads or obsolescence. 
Repair of the sewer structure may be accomplished by 
the use of: 

(1) pneumatically applied mortar (shotcrete) 

(2) portland cement concrete 


(3) portland cement grout 


PNEUMATICALLY APPLIED MORTAR. Many old 
masonry sewers have been repaired and renewed by the 
use of pneumatically placed mortar (shotcrete) at a very 
reasonable cost. St. Louis, Mo. in 1927 and 1928 repaired 
a number of 60- to 75-year-old masonry sewers with pneu- 
matically placed mortar. 

In 1948, Bloomington, Ill. repaired some old masonry 
sewers 48 to 96 in. in diameter by placing 2 to 4 in. of shot- 
crete at a cost varying from 41 to 54 cents per sq.ft. per in. of 
thickness applied. Savannah, Ga. in 1949 repaired (by this 
method) an old concrete box sewer constructed in 1917. It 
is believed that at least 30 years were added to the life of 
this sewer by the application of 2 in. of shotcrete. 

The thickness of shotcrete required will depend upon 
the structural condition of the sewer. Normally, 34 to 1% 
in. is sufficient although any thickness that can be economi- 
cally justified can be built up by the application of successive 
layers. 

All scaled or disintegrated parts of the sewer should 
be removed and the surface cleaned by sand blasting of 
other methods before the shotcrete is applied. 


Repairs to Savannah, Ga. sewer in 1949. Left—showing wire mesh in place after 
removal of loose unsound material and Right—showing shotcreting operation. 


Wire mesh reinforcement in amounts of about 0.4 of 
1 per cent of the cross-sectional area of lining in each direc- 
tion is used. Usually wires are spaced about 4 in. center to 
center both ways and are held in place by anchors embedded 
in the sewer wall structure spaced at about 36-in. intervals.* 


CONCRETE. The sewer structure may be repaired or 
strengthened by a layer of concrete. Concrete may be placed 
by shovels or buckets or pumped into place. Precast pipe 
have been used successfully as liners for old sewers. 


CEMENT GROUT. Repair of the sewer structure may 
also be done by grouting previously placed coarse aggre- 
gate.** In some cases excessive leakage at joints or cracks 
may be reduced by pressure grouting. Grout may be forced 
behind the sewer through holes drilled from the inside. 
Where that is impractical, as in small sewers, grout may be 
forced through pipe provided with wellpoints extending 
from the ground surface to the sewer structure.* ** 


*A more complete discussion may be found in Shotcrete, published 
by the Portland Cement Association, available free on request. Dis- 
tributed only in U.S. and Canada. 

**]J. W. Kelly and B. D. Keatts, “Two Special Methods of Restoring 
and Strengthening Masonry Structures”, ACI Journal (Feb. 1946), 
page 289. 

****Soil Stabilized by Grouting”, New England Construction (Oc- 
tober 1949), page 46. 


Sewer Appurtenances 


Maintenance of sewer appurtenances should not be neg- 
lected. Frequent cleaning of catch basins on storm and com- 
bined sewer systems will prevent grit deposits from reaching 
the sewer proper. Inlets should be cleaned to permit the free 
entrance of storm water. Siphons, creek crossings, flush tanks 
and outlet structures all require frequent inspection and 
maintenance to insure efficient operation. 


Safety Precautions 


In addition to the regular safety equipment supplied to 
men working in sewers, special equipment to determine the 
concentration of toxic and combustible gases and oxygen 
deficiencies should be provided to all sewer maintenance 
crews. 

Every sewer department should have a map showing 
the location of sewer lines, house connections, manholes, 
catch basin units, etc., as well as records of size, grade and 
depth of sewers. Good maps save time and reduce damage 
to property when repair or extensions to sewers become 
necessary. 


PAGE 4/7 


TABLE 18 SUPPORTING STRENGTH OF CONCRETE PIPE* 
per linear foot of pipe in thousands of pounds (kips) 
Standard Strength Extra Strength Reinforced Conc. Reinf, Cone, Cataiins 
- A A C 76-55 
ASTM Concrete Sewer Pipe Concrete Sewer Pipe Sewer Pipe Safety|Faciors ia 
Spec. No. C 14-58 C 14-58 C 75-55 i 
Safety Factor= 1.5 Safety Factor= 1.5 Safety Factor= 1.0 Standardisironatn Extra Sonam 
Bedding 
Class D C B A D Cc B A D (e B A D Cc B A D (e B 
Bedding 
Factor 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 


6 O.8 al 1402.2 Sie eon 20min. ue 4.0 


8 O91 Si) 1 Oge2 Ont lo aie 2. On anee. 3 alee 


10 TOG ts40) 1.8) We 2.8 2. Ons 2: ae 420 


12 1.1 | 1.5 [| 1.9) 3.001 1.6) 2.20152.8° ' 4,552.05) 2.7 103.49 5.4 2 O es, 4 ea ore 


Le) P29 1,7 (e229 3.5 W 2.0%" 2.8 3.5. W525 1) 2:2 583.0 0s s OmlenO.0 Meares, 


18 1:4] 2.0 | 2.5 | 4.0] 2.4 | 3.3 | °4.2 ) 6.6 1 2-4. 1353) 4.25) 6.6 63.3 Alone 37a 


e 2141.61 2.24) 2.8 44 O84) SBA ome7.8 "2.6 es oumes came? ie me: 

& 24 | 17] 24] 30 | 48) 33] 44 | 66] 88 | 26 | 3.6 | 46 | 7.2] 3.3| 4.5) 57] 9.0] 44) 6.0) 76ime 

“ 27 | | 2.80 3,8 aA. 8 sine 747, aa 

; 30 3.0 | 4.1 | 5.1] 8.1] 3.7 | 5.1 | 6.4/10.1] 5.5] 7.5| 9.5) tom 

Be | 3114354 ees a 

: 36 33| 45157 | 9.0] 45| 61 | 7.71122] 66] 9.0/11.4| 180 

242 | | | | 35 48 61 96) 5217.1 | 90/142) 77/10.5/13.3|210 
48 | 37 5.1 65 102) 59| 8.1 1103/1621 88|12.0|15.2| 240 
54 | | 4.1 | 5.6 | 7.0 }11.1| 64 | 8.8 |11.1/17.5) 9.9|13.5| 17.1) 200 
60 | 4.4 | 6.0 | 7.6 | 12.0] 6.6 | 9.0 |11.4]18.0] 9.9] 13.5 | 17.1 | 270 
66 | | | 47 | 64) 8.1 127) 69 | 9.4|12.0|18.9| 10.5|14.3/18.0| 285 
72 | | | | | 50 68 85 135) 73 | 9.9 |12.5|19.8| 10.9|14.9| 18.8| 29.7 


*Supporting strengths shown in table are for concrete pipe meeting ASTM specifications (3-edge bearing test) and include safety and bedding factors as indicated. 


Example: Use of Tables 

Assume a 15-in. diameter concrete pipe is to be laid in a 
3-ft. wide trench under 10 ft. of cover. The backfill material 
has a unit weight of 120 lb. per cubic foot and Class B bed- 
ding is specified. 

To determine the backfill load, W., refer to Table 11 on 
page 28. For H equal to 10 ft. and a 3-ft. wide trench, it is 
seen that W, is 2,200 lb. per linear foot. From Table 18 on 
this page it is seen that a 15-in. nonreinforced concrete sewer 
pipe, standard strength (C14-58), with Class B bedding, has 


PAGE 48 


a supporting strength of 2,200 Ib. per linear foot, and thus 
will carry the expected load. 


Table 18A gives supporting strengths for reinforced 
concrete sewer pipe (C76-57T), and it is seen that 15-in. 
diameter Class II pipe with Class B bedding has a supporting 
strength of 2,400 Ib. per linear foot, and could be used if 
desired. 


It is obvious from examination that all of the stronger 


pipe classifications in the tables would also support the load 
given in the example. 


\BLE I8A 


CLASS | 


CLASS Il 


1.5 1.9 
Lect: bay, 
1.9] 2.4 
22428 
2.6| 3.3 
3.0| 3.8 
3.4| 4.3 

3.7| 4.7 


41| 5.2 


vO Be WA 


5.2| 6.6 


6.0| 7.5 


6.7| 8.5 


Reinforced Concrete Sewer Pipe C 76-57T 
Safety factor= 1.0 


3.0 
3.0 
3.8 


4.5 


5.2 


6.0 


6.8 


7.5 


8.2 


9.0 


10.5 
12.0 


13.5 


4.0| 5.1 
4.6| 5.8 
5.1} 6.4/10.1 


Based on 0.01” Crack 


CLASS Ill 


SUPPORTING STRENGTH OF CONCRETE PIPE* 


per linear foot of pipe in thousands of pounds (kips) 


CLASS IV 


1.9 | 3.0 


3.8| 6.0 


6.7 | 10.5 


7.6 | 12.0 


8.5 | 13.5 


951150 


10.4 | 16.5 


11.4 | 18.0 


13.3 | 21.0 


15.2 | 24.0 


17.1 | 27.0 


CLASS V 


5:6) 97.1) 41.3 


6.6| 9.0| 11.4 | 18.0 


9.9 | 13.5 | 17.1 | 27.0 


Internal Viameter of Fipe, inches 


7.9 (19-9 


8.2 | 10.4 


9.0 | 11.4 


9.7 | 12.3 


10.5 | 13.3 


11.2 | 14.2 


12.0 | 15.2 


16.5 


18.0 


19.5 


21.0 


22.9 


24.0 


12.7 | 16.1 
13:5 137.1 


2o03 


27.0 


18.2 | 23.1 | 37.0 | 


19.0 | 30.0 


21.0 | 33.0 


22.8 | 36.0 


24.7 | 39.0 


26.6 | 42.0 


*Supporting strengths shown in table are for concrete pipe meeting ASTM specifications (3-edge bearing test) and include safety and bedding factors as indicated. 


PRINTED IN U.S.A. 


C 10-2 


j- 
< 
U 
Oo 
wr 


Ny eee. ee rea | 


concrete 
chore 
protection 


PORTLAND CEMENT ASSOCIATION 


Reale Rigen aR HERRELOAS 


Eee a same inca ‘ 3 ! gins Re serdar Re TO, Saale Se s 
‘ ‘ 4 ale pene ee fo ieee & Os at asl ; 


GP 


ons spo 
se en as 


mpa Bayshore seawall, Tampa, Fla., was built in 1938. Designed by F. H. Horton. 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technic 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold progra 
of the Association and its varied services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, engaged 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on reque: 


Copyright 1955 by Portland Cement Association 


i oe 


1 SERA ORL E et, 


— ! 


Section Page 
STTELOCUCTION Tee eee ee, ee ee a Pe 
Hes OTMGL MOLES em WATERCO RP od te PON Seilig ctde, OLE Moe 
Ua ty ARIS hs Se AN Oe ca ae ee 


2. Wave Action 


8 
Wave Characteristics 8 
Peres Or tere etl py eNO dic As) vat, late een om ipl ado 
Effects of Winds 9 
Wave Analysis . 9 


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OR CUEVy ACS mentee ia ue TOM at het He Nak. Pec WEE 
INO LMeR ITO AVES UN Meee ei me ROP Wala hcl BD 
resi Mm BCC UIrements jeune pK imei teh el Mat ys hu LL 
3. Shore-Protection Structures. . ....... .18 
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Concrete pipe groin, Milwaukee, Wis., was built by Milwaukee County Regional Planning Department. 


Some of the designs shown herein are patented. The Portland Cement 


Association, however, has no information concerning these patents. 


ROTECTION of our coastal and inland shore- 
lines against the tireless, destructive forces of turbulent 
waters has been a problem for more than three-quarters 
of a century. As long as waterfront development was 
confined to natural harbors and the shoreline adjacent 
to them, the problem was of spécial significance only 
to the localities concerned. But with the development 
of our highway systems, particularly those scenic drives 
bordering the shores, the more remote properties along 
the shorelines were improved. This ever-increasing use 
of our shorelines has necessitated maintaining the ad- 
jacent beaches at their present locations. To protect 
both private and public property, beach erosion must 
be prevented and eroded beaches must be repaired 
wherever economically possible. 


Introduction | SECTION 1 ~ 


When faced with ruinous erosion, beach-front prop- 
erty owners, both public and private, have frequently 
followed the quite natural tendency to accept almost 
any suggestion for protection. Usually such suggestions 
are not the result of a careful study of the problem by 
competent engineers, but are merely transpositions of 
structures that have been successfully used at other 
locations where conditions may have been different. 
Such practices have frequently aggravated the very 
conditions they were intended to alleviate. 

Basically, all shoreline erosion is caused by two 
natural actions of the water: incoming waves and lit- 
toral currents.* But studies of many instances of ero- 


* Littoral current is the current near the shore of an ocean or 


lake. 


Concrete permeable groins, Milwaukee, Wis., shown under construction, were built by the Milwaukee County Regional Planning Department in 
1933. Photograph shows the offshore section in place. 


By 1944 a considerable beach, as shown, had been formed as a result of these groins despite the fact that the water level in Lake Michigan was 


three feet higher than in 1933. Today, 22 years after their construction, this beach is still in excellent condition even though the lake level has 
risen an additional foot since 1944. 


sion and of failure of structures that were intended to 
prevent the erosion have revealed the complexity and 
great variability of these natural forces. The engineer 
must draw extensively from the sciences of oceanog- 
raphy, meteorology, fluid mechanics, soil mechanics, 
structural design, geology and others to learn about 
these forces and to deal with them. Therefore, it is only 
common sense to take advantage of the knowledge of 
qualified experts in designing such work. The cost of 
their services is a proportionately small part of the con- 
struction cost of protective measures and of the value 
of the property to be saved. 

In recognition of the public interest in beach erosion 
and of the fact that coastal engineering is a specialized 
field, the Seventy-First Congress under Public Law 
No. 520 (July 3, 1930) directed the Chief of Engineers 
of the U.S. Army to investigate and study cooperatively 
with local political subdivisions the erosion of the 
shores* of the United States. Subsequent legislation 
has extended the research to be undertaken by the 
Beach Erosion Board.** In 1946, Congress for the first 
time authorized the expenditure of federal funds for 
the construction of erosion protection projects for pub- 
licly owned beaches (21) 4 Such federal participa- 
tion cannot exceed one-third the total cost and each 
construction project must be specifically authorized 
by Congress. 

While federal funds cannot be expended to protect 
private beaches, the studies conducted by the Beach 
Erosion Board are of material benefit to property own- 
ers in the area covered by such studies in the design 
and construction of protective works. Construction of 
protective structures on public beaches may or may 
not benefit nearby private property. 

An important part of the duties of the Beach Erosion 
Board is “to publish from time to time such useful 
data and information concerning the erosion and pro- 
tection of beaches and shorelines as the Board may 


Shore or beach 


Foreshore|Backshore 
r 


Shoreface or inshore 


shoreline 


Hightide 


Vee oo 

a a 

oS > o 
ef (4 
oo = 
Et aT 
ow E ro] 
P= S] °o 
On oO 


Fig. 1. Shore profile illustrating terminology usually used in coastal 
engineering. 


deem to be of value to the people of the United States.” 
Many studies by the Board and by others have been 
published. The most extensive single publication is 
Shore Protection Planning and Design, Technical Re- 
port No. 4 of the Beach Erosion Board (1). This pub- 
lication of approximately 400 pages is a comprehensive 
collection of published and unpublished experimental 
data and information from individuals, state and local 
bodies, the Corps of Engineers and other federal agen- 
cies and is intended to serve as a guide for the coastal 
engineer in the planning and design of shore-protec- 
tion structures. Since it covers the field so completely 
it should be referred to for specific and detailed infor- 
mation on waves and their effect on shorelines and pro- 
tective construction. 


Erosion of Shores 


Surveys and photographs taken over a period of time 
clearly reveal that the natural processes of erosion are 
constantly at work along our shorelines. Conversely, 
the effect of man-made structures can also be seen, 
sometimes very strikingly, in such surveys and photo- 
graphs. 

Although tides and other changes in water levels 
change the zone of wave attack on beaches, the prin- 
cipal forces causing changes in beaches are waves and 
currents that transport and deposit sediment. Some of 
this material is transported by littoral currents and de- 
posited along the shore, while other material is moved 
offshore and deposited at greater depths. 


Littoral Drift ¢ 


The direction and rate of movement of littoral drift 
depend largely on the direction and energy of waves 
approaching the particular location and on the type 
and amount of material available. Quantities of eroded 
and deposited material may be as much as 300,000 to 
400,000 cu.yd. per mile of beach per year. The actual 
rate of net loss or gain can best be determined by 
comparing successive surveys. In the case of net gain 
at a particular location a petrographic analysis of the 
material will often reveal its source. 


* In this law and subsequent legislation, the word “shores” 
has been defined to include all the shoreline of the Atlantic and 
Pacific oceans, the Gulf of Mexico, the Great Lakes, and lakes, 
estuaries and bays directly connected therewith of the continen- 
tal United States and its territories. 


** The Beach Erosion Board consists of four officers of the 
Department of the Army, Corps of Engineers, and three engi- 
neers of cooperating state agencies charged with beach-erosion 
control and shore protection. Beach Erosion Board headquarters 
are located at 5201 Little Falls Road, N.W., Washington 16, D.C. 


+ Numbers shown in this manner refer to bibliography at end 


of book. 


t Littoral drift is the material that moves along the shoreline 
under the influence of waves and currents. 


“SECTION 2 | Wave Action 


Wave Characteristics 


THE FACTORS used to define a wave’s characteristics are 
height, period and length (16). Wave height (H) is de- 
fined as the vertical distance between the crest of a 
wave and the preceding trough. The wave length (L) is 
defined as the horizontal distance between successive 
wave crests measured perpendicular to the crests. The 
wave period (T) is defined as the time required for 
a wave crest to traverse a distance equal to one wave 
length. 


L= Length 
Wave crest— ny 


Fig. 2. Wave characteristics. 


Effects of Water Depth 


Waves moving in depths greater than half their length 
are known as deep-water waves (1, page 1) and are 
unaffected by the water depth. As the deep-water waves 
move in toward the shoreline their characteristics are 
modified by the decreasing depths of water. That part 
of the wave crest advancing in shallower water moves 
more slowly than that part still advancing in deeper 
water; this causes the wave crest to bend toward align- 
ment with the underwater contours. This is called re- 
fraction (1, page 29). Refraction changes the direction 
and intensity of wave attack on the beach- or shore- 
protection structure (2, page 33), (3, page 97). 

In passing natural shoreline features, such as head- 
lands, waves diverge and lose energy; this results in 
deposition of materials, which builds beaches up in 
such protected areas. 

When a portion of an otherwise regular wave train 
passes a barrier, such as an island or breakwater, dif- 
fraction causes waves to be propagated into the shel- 
tered region formed by the barrier. Diffraction (1, 
page 39), (4, page 6) is defined as a phenomenon by 


which energy is transmitted laterally along a wave 
crest, essentially stretching the wave action into the 
lee area of the barrier even though the barrier has 
stopped the waves from getting there from the sea- 
ward direction. 


Effects of Winds 


Waves are generated by winds (1, page 2). Their char- 
acteristics can be determined by the velocity of the 
wind, its duration and the fetch length. These factors 
are determined by an analysis of synoptic weather 
charts as shown in Fig. 3, where the isobars are ex- 


140° 135° 130° [25° 120° 115° 


Pt.Arguello 


Fig. 3. Typical surface synoptic chart used for forecasting wave char- 
acteristics. 


pressed in millibars. The fetch length (F) is the hori- 
zontal length of the generating area (in the direction of 
the wind) over which the wind blows. As the waves 
leave the generating area and move toward the shore, 
they pass through calmer water. This is known as the 
decay distance (D). In this area the wave height de- 
creases and the wave length increases. Moreover, wave 
characteristics may be altered by cross, opposing or 
following winds, or they may be altered by waves from 
other generating areas (5), (6), (7). 


This huge boulder was thrown on top of, and almost over, this concrete 
jetty—a striking demonstration of the energy contained in wave action. 


—Photograph courtesy of the Beach Erosion Board. 


Wave Analysis 

In view of the preceding discussion, it is easy to under- 
stand why coastal engineering is one of the most com- 
plex fields of hydraulic engineering. In the years past, 
a number of theories of wave motion covering simple 
regular waves have been advanced (8). 

Wave-energy formulas, derived from theoretical con- 
siderations of uniform series of waves having equal 
dimensions, are of little use to the designer of protec- 
tive structures. Such formulas do indicate, however, 
that wave energy increases very rapidly with increase 
in wave dimensions. Fortunately, because of turbu- 
lence, refraction and diffraction, only a portion of the 
total energy remains per linear foot of wave crest when 
it reaches the shore or a protective structure. As a wave 
approaches the shore it reaches shallow water, breaks, 
moves on in, breaks again in shallower water, encoun- 
ters adverse currents or backwash from preceding 
waves, is refracted over hydrologic features, opposes 
reflected waves and finally expends its remaining en- 
ergy upon the beach or other obstruction. In the case 
of waves breaking directly on the structure, the struc- 
ture must be able to withstand a considerable portion 
of the initial force of the waves. 

Of more practical use to coastal engineers are tech- 
niques developed during World War II to forecast 
wave action on beaches for use in the amphibious land- 
ing of troops. These techniques have been adapted to 
estimate from synoptic weather charts and from refrac- 
tion and diffraction diagrams wave characteristics for 
the design of protective structures. It is not the purpose 
of this booklet to describe the complex mechanics of 
this method, which are fully explained in Shore Protec- 
tion Planning and Design, Technical Report No. 4 of 
the Beach Erosion Board (1). Suffice it to say that the 
method requires considerable skill and experience if 
the results are to be of value in determining wave char- 
acteristics for the design of shore-protection structures. 

After the wave characteristics have been determined 


9 


by this method, the wave pressure and its point of ap- 
plication can be estimated for the type of wave expected 
at the site of the structure. Structures may be subjected 
to three types of wave action—breaking, broken and 
nonbreaking (1, page 117). 


Breaking Waves 


Waves that break directly upon the structure exert a 
combination of hydrostatic and dynamic pressures. The 
Minikin method (1, page 124), developed in 1946 for 
determining dynamic pressures, is recommended as 
presenting the closest approach presently known to 
the actual pressures caused by breaking waves. 


Broken Waves 


Protective structures that are built above normal high 
water may be so located that during high tides and 
storms waves will break before reaching them. Such 
waves will exert pressures on the structure that are 
partly dynamic and partly static. (1, pages 125-130.) 


Waves are breaking on and overtopping a concrete breakwater. 


Air—entrained 
concrete 


+0. 


Fig. 4. Section of seawall at Duxbury Beach, Mass. 


This seawall at Duxbury, Mass., was 
built above normal high tide by the 
State Division of Waterways. How- 
ever, during violent storms broken 
waves may reach the wall. 


Nonbreaking Waves 


Ordinarily, storm waves would break in the depth in 
which the structure is located. However, in protected 
regions where the available fetch is limited, nonbreak- 
ing waves may occur. In such cases, nonbreaking waves 
form a clapotis, or standing wave, in front of the struc- 
ture; hence, the forces exerted are essentially hydro- 
static. The Sainflou method (1, page 118) is the most 
commonly used to determine the maximum and mini- 
mum wave pressures of these waves. In the case of a 
vertical-face seawall in front of which a standing wave 
is formed, it should be expected that immediately in 
front of the wall the beach will be depleted to a level of 
approximately one wave height (H) below low water 
(9, page 221). 


Design Requirements 


The design procedure for a shore-protection structure 
follows the conventional methods of structural design 
after the wave characteristics have been forecast and 
their pressures determined as discussed above. 

It is evident that loadings for sea structures cannot 
be determined as accurately as those for land struc- 
tures. Therefore, the safety factor should, in general, be 
larger for sea structures than for similar land structures. 
Of course, fundamental requirements for wall stability 
must be met in both cases. All forces—including hydro- 
static uplift—that act on a structure must be determined 
and the most severe combinations of these considered. 
The wall then must be stable against: 


1. Overturning. 


This would be achieved if an increase of 50 per cent in 
the worst combination of overturning forces does not 


produce foundation pressures that would exceed the 
bearing value of the soil. If the resultant of these forces 
falls outside of the middle third of the actual base, the 
structure would still be safe against overturning on the 
provision that the allowable pressure on the soil, when 
computed on the effective base, is not exceeded. The 
effective base is defined as three times the distance 
from the toe to the point where the resultant intersects 
the base. 
2. Sliding. 

Sliding resistance, including friction between base and 
foundation plus passive resistance of backfill material, 
should be at least twice the total horizontal active pres- 
sure; and the angle between the resultant of all forces 
and the vertical should be less than three-fourths of 
the angle of repose of the foundation material. 


3. Structural weakness. 


All members of a structure should be designed to resist 
the loads and forces acting on them and should be 
constructed of strong, durable materials. 

The upward pressure of waves after they break on a 
structure is dissipated into the air and is of no conse- 
quence in design unless the waves overtop the structure 
in appreciable amounts, in which case the protection 
of the top and the back of the wall from water is impor- 
tant. The stability of the wall may be threatened by 
water back of it that may induce sufficient lateral pres- 
sure to tip the wall forward. There is also the possibility 
that water thus impounded may remove light erosible 
foundation material through open joints, leaving the 
wall vulnerable to wave pressure. The quantity of water 
carried back of the wall is important in the design of 
the drainage system behind the wall. 


WW 


The amount of overtopping will depend on the height 
(1, page 89) and shape of the structure and the height 
and period of the waves reaching the structure. The 
Beach Erosion Board is conducting model studies to 
determine the efficiency of the shape of seawall faces 
in preventing overtopping (10, page 261). 


Right—Seawall and walk at Neptune Beach, Fla., were damaged by a 
violent storm on October 6, 1947. Water overtopping the wall induced 
high lateral pressure back of it that caused the wall to tip forward 
and the sidewalk to collapse. 


Below—Waves are overlapping a shore-protection structure at Point 
Place, Toledo, Ohio, during a winter storm. Note the flooded condition 
of the area in the background. 

—Sketch made from photograph courtesy of the Beach Erosion Board. 


oh za Shore-Protection Structures | SECTION 3_ 


Fundamental Considerations 


SHORE-PROTECTION structures vary in purpose and type 
of construction. No two shores are exactly alike; hence, 
special design of coastal works must be prepared for 
each individual site and must take into consideration 
a complete analysis of all factors involved, including 
basic oceanographic information and coastal sediment 
problems. 

Case histories of the performance of structures on the 
shores of the United States have dramatically shown 
that they have often failed to function as expected. 
Therefore, for satisfactory results, it is important that 
studies be made and that the structures be designed and 
constructed under the direction of competent coastal 
engineers. 

Shore-protection structures fall into three general 
classifications: offshore structures, protective beaches, 
and onshore structures. Each has a specific purpose to 
accomplish. 


Shore-protection structures at Cor- 
pus Christi, Texas, comprise seawall, 
groins and revetments. The stepped 
seawall, built in 1938-39, protects: 
the city from tidal waves. 


Offshore Breakwaters 


Breakwaters are defined as structures protecting a har- 
bor, anchorage or basin from waves. They are free- 
standing structures located in varying depths of water 
and usually they are exposed to unobstructed wave 
action. The seaward face must resist the action of break- 
ing storm waves and the high internal hydrostatic pres- 
sures developed under the troughs of the wave train. 
These faces, though built as steep as 1% to 1, may erode 
until they are as flat as 10 to 1, while that portion below 
the level of wave attack may ultimately be as steep as 
1 to 1. To be stable, they must be massive. The high 
cost of breakwaters precludes their normal use for shore 
or beach protection. However, they may be required 
in certain instances to protect or maintain the toe of a 
beach or to trap littoral materials. 

The rubble-mound type of breakwater has its origin 
in antiquity; usually it was constructed of large volumes 
of massive, dense, abrasion-resistant stone. Now, many 


Concrete Anti-Erosion Rings were used at Fairport, Ohio. These rings, 
designed by Alton E. Tear, are 2 ft. high and 60 in. in diameter with 
a 6-in. wall thickness. 


Tetrapods stored prior to installation at La Nouvelle, France. These 
units, each weighing 15 tons, replaced 30-ton blocks, and were devel- 
oped by the Neyrpic Hydraulic Research Laboratory, Grenoble, France. 


Same type of tetrapods as shown in 
photograph above were used to 
protect the toe of a concrete sea- 
wall at Sousse, Tunisia. 


14 


breakwaters of the rubble-mound type are constructed 
of concrete and stone. The concrete consists of a cap, 
core wall or superstructure surrounded or supported 
by rubble stone. 

Concrete may be used for the entire structure when- 
ever the foundation is firm and no settlement is ex- 
pected. On yielding foundations, it is customary to 
place stone layers of varying thicknesses and to allow 
them to become stable before placing the concrete 
superstructure. Where wave action is comparatively 
mild, caissons filled with stone or sand and capped with 
concrete, as well as concrete pipe or rings, have been 
successfully used as breakwaters. 

Where rock in adequate quantities or of adequate 
size has not been economically available, large precast 
concrete block of various shapes have been used; the 
most common shapes are the cube and the tetrahedron. 
Recently, in Europe, a shape known as a “tetrapod” 
(12) has been patented and used for breakwater and 
jetty construction. The tetrapod resembles a child’s jack 
and consists of a central body from which four trun- 
cated cylindrical legs radiate at a 120-deg. angle to 
each other. When in place, the legs of adjoining tetra- 
pods interlock with each other and present a very rough 
surface that reduces wave runup and reflections. The 
large openings between the interlocking legs prevent 
hydrostatic back pressures, guaranteeing immobility of 
the unit and thus assuring stability of the structure. 
Tests indicate that comparatively lightweight tetrapods 
will outperform much heavier block and are stable on 
a 1-to-1 slope even under heavy wave action. 


Protective Beaches 

Protective beaches, as the name implies, protect the 
lands behind them by absorbing the effects of the 
waves impinging upon the beach. They are the most 
effective means of dissipating wave energy. 


Beaches are made up of materials eroded from the 
back shore, brought in from deeper water or supplied 
by rivers and streams. These materials are constantly 
moving, being carried along the beach by littoral cur- om a 
rents or being carried seaward or shoreward by the ac- ot ae een Me ee a 
tion of waves. Whenever an analysis reveals that there —, 
is sufficient littoral material available, the use of groins 
may restore or maintain a beach. 

Groins are shore-protection structures, usually con- 
structed perpendicular to the shoreline, for building 
or widening a beach by trapping littoral drift, or for 
protecting a beach by retarding loss of beach materi- 
als. The use of groins should be decided on only after 
careful consideration of the problem and the many 
factors involved. The principal factors to be consid- 
ered are, briefly: 


tia 


1. The extent of probable damage to the downdrift 
beach. 

2. The amount and rate of littoral drift. 

3. Adequacy of the shore anchorage of the groins to 
prevent flanking. 

4. The permissible variations in the shoreline that 
may result from variation in direction of wave 
attack. 

5. Economic comparison with other shore-protection 
methods. 


Groins are relatively narrow and may extend from less 
than a hundred feet to several hundred feet into the 
surf from a point well landward of any possible shore- 
line recession. The inshore section of the groin is usu- 
ally horizontal, with the landward end protected by a 
bulkhead, seawall or revetment, or extended into the 
existing bluffs to prevent flanking by severe storms. If 
it is desired to maintain a sand supply downdrift of a g 

; : : : l 1 A light, permeable groin at Boca Raton, Fla., was constructed in 1935. 
groin, the top of the inshore section is usual spas aced This groin was designed by Colonel G. A. Youngberg and consists of 
at an elevation that will permit movement of beach cast-in-place pilasters and precast concrete members. 


Reinforced concrete pipe breakwater 
at South Haven, Mich., was con- 
structed in 1953 of 48-in. diameter, 
4-ft. long concrete pipe that were 
not filled or capped. It has proved 
effective in halting beach erosion 
at this location. The breakwater 
was designed by Max L. Norris. 


15 


Unusual arrangement of precast units is an impermeable groin installation built on Presque 
Isle peninsula at Erie, Pa., by the L. A. Wells Construction Co. of Cleveland in 1953. 


material over it during storms or at high tides. The in- 
termediate section extends from the end of the hori- 
zontal inshore section to as near low water as construc- 
tion practices will permit. Its top is placed parallel to 
the normal slope of the particular beach. It may or may 
not require an outer horizontal section, depending on 
the extent to which it is desired and is practicable to 
interrupt the littoral drift. Strong littoral currents may 
require this end section to protect the entire structure. 

The spacing of groins may be estimated from exist- 
ing groins in adjacent areas. If there are no nearby ex- 
isting groins, the spacing should be determined by 
methods described in Shore Protection Planning and 
Design, published by the Beach Erosion Board (1, page 
102). Generally the spacing will vary from one to three 
groin lengths. 

Groins may be permeable or impermeable. Perme- 
able groins permit the passage of some sand through 
them even at times of low tide and relatively still water. 
Impermeable groins are solid or nearly solid structures 
that prevent the passage of littoral drift through them. 

Permeable groins have been used in a number of lo- 
calities, specifically in the Great Lakes, New York and 
Florida areas. Under certain conditions (1, page 100) 


16 


bee 
Fa OS 


some have not been as efficient in building, maintain- 
ing or protecting a beach as expected. 

Permeable concrete groins of precast units were 
built in Lake Erie near Cleveland in 1945 with the ex- 
pectation of forming a beach. While the photograph 
(above, center) shows practically no beach accretion 
the erosion of the bluff has been controlled and the 
shoreline has been preserved. 

Another recent Great Lakes installation of permeable 
groins built with precast units is near Bradford Beach 
at Milwaukee, Wis. This new type of groin, shown in 
the photograph (above, right), is made entirely of pre- 
cast concrete units assembled at the site. Fig. 5 shows 
details of groin assembly. Air-entrained concrete was 
used in the units for the upper portions, where exposure 
to severe freezing and thawing could be expected. 

The unusual combination of groin and fishing pier 
was successfully accomplished in the structure illus- 
trated in the photograph on page 18. This structure 
was built by the city of Clearwater, Fla., entirely of pre- 
cast concrete units. Panel units were jetted into place 
between concrete piles in alternate bays for the first 
300 ft. to form baffles that would slow down the littoral 
currents and cause deposition of beach materials. In 


Permeable concrete groins were installed in 1945 at | 
cast units, were designed by Sydney Makepeace Woo: 


Cleveland, Ohio. These groins, which consist of pre- Permeable groins of precast units designed and installed in 1945 by Milwaukee County 
Regional Planning Department near Bradford Beach, Wis. Fig. 5 shows details of assembly. 


SECTION A-A 


Fig. 5. Details of Bradford Beach groin assembly. 


17 


Combined permeable groin and fishing pier was built at Clearwater, Fla., in 1953. Designed by S. Lickton, city engineer. 


addition to restoring all previous erosion losses, this 
groin-pier has materially widened the beach. 

Impermeable groins have demonstrated their value 
in building up and maintaining beaches in many places. 
For example, the groins shown in the photographs to 
the right have been phenomenally successful in build- 
ing a beach at Chagrin Harbor, Ohio, in the three years 
since their construction. These groins are built of con- 
crete units 10 ft. long, 5 ft. wide and 8 ft. deep with in- 
terlocks formed on both ends. The project was built 
by L. A. Wells Construction Co., Cleveland, under the 
direction of F. O. Kugel, chief of the Division of Beach 
Erosion of the State of Ohio. 

Precast concrete block groins of a design shown in 
Fig. 6 were used in the construction of groins in several 
locations in the New York area. The installation at East 
Hampton, N.Y., shown in the photograph on page 19, 
shows how two sizes of block were placed in such a 
relation to each other that they present a roughened 


18 


Beach at Chagrin Harbor, Ohio, in 1951, before completion of imper- 
meable groins of precast concrete interlocking units, similar to those 
used at Presque Isle peninsula as shown in photograph on page 16. 


Impermeable groin of precast concrete block at East Hampton, N.Y., 
was built in 1953. Details of the block and joint are shown in Fig. 6. 


Chagrin Harbor beach three years later. 


I"* Lifting eyes 


Channels 


L 650" . 
ISOMETRIC VIEW 


Fig. 6. Concrete groin block. 


surface to the wave as it moves along the groin. Each 
block contains 5% cu.yd. of air-entrained concrete. The 
block were placed on a mat of small-sized stone to pre- 
vent them from burying themselves in the sand. Addi- 
tional protection was provided by large-sized riprap, 
as shown. Groin assembly of these precast units, done 
with simple construction equipment, is very rapid. 
Concrete pipe have also been used to form groins. 
The photograph (top, page 20) shows a typical concrete 
pipe groin constructed in 1953 by the Milwaukee Coun- 
ty Regional Planning Department at South Shore Park. 
Each groin has 82-in. pipe on the shore end, 42-in. pipe 
in the central portion, and 60-in. pipe in the offshore 
section. The lengths of these groins vary. Alignment is 


Concrete pipe groin at South Shore Park, Milwaukee, was constructed 
in 1953. Although there is not sufficient littoral drift available to build 
a beach, the groins protect the shore against further erosion. 


453) Concrete cap 


- Tierods and 
- Gravel fill channel wales 


\- in each pipe 


Lake bottom 


Sy 


SECTION 


Fig. 7. Concrete pipe groin, South Shore Park, Milwaukee, Wis. 


Fifteen-ton tetrapods were placed to 
protect the ends and sides of a jetty 
at Casablanca, Morocco, Africa. 


20 


maintained by the use of steel beams and tierods. De- 
tails of construction are shown in Fig 7. 

Jetties differ from groins in that they are much longer 
and much more massive. They are placed in the en- 
trances of harbors to protect the channels used by ships 
and at the mouths of rivers to assist in the mainte- 
nance of a channel to discharge river flows. They affect 
beaches in that they may completely intercept all littoral 
materials. To prevent starvation of downdrift beaches, 
it may be necessary to provide for mechanically by- 
passing a certain percentage of these materials. 

Jetties, like groins, have been built of precast and 
cast-in-place concrete. Concrete tetrapods are reported 
to have been used successfully and economically in 
jetty construction at Casablanca, Morocco, Africa, to 
protect a seawater inlet. 


Onshore Structures 


Onshore structures are placed approximately parallel 
to the shoreline and include seawalls, bulkheads and 
revetments. Seawalls are comparatively massive struc- 
tures placed to protect upland areas from violent wave 
action. Bulkheads are ordinarily of lighter construction 
because their primary function is to retain a fill. Revet- 
ments are facings of stone, concrete, etc., built to pro- 
tect a shore or beach against erosion. 

Seawalls are built of concrete in a variety of designs 
depending on conditions at the site, such as tidal ranges, 
foundation materials and wave characteristics. Gener- 
ally, seawalls are gravity-type structures. 


Vertical-face concrete seawall was built 25 years ago at Watch Hill, R.I. This seawall, combined with heavy rock riprap, protects the private resi- 


dence on hill at right. 


There is a wide variety in the shapes of the walls’ 
exposed faces. The character of the property to be 
protected will influence the architectural treatment. 
Seawalls have been built with exposed faces that are 
vertical, nearly vertical, convex, concave, backward 
sloping, re-entrant, or stepped. Each shape has its ad- 
vantages and disadvantages; hence, combinations may 
be employed that meet the conditions of the particular 
Site. 

A small, vertical-face reinforced concrete seawall, 
as shown in the photograph at the right, was built in 
1952 near St. Joseph, Mich., to protect a bluff overlook- 
ing Lake Michigan. The seawall is 190 ft. long, 5 ft. 
high and varies in thickness from 18 in. at top to 24 in. 
at bottom. The contrast between the comparatively fine- 
grained beach material retained by the wall and the 


This small reinforced concrete seawall protects part of a private bluff 
overlooking Lake Michigan. Photograph taken one year after construc- 
tion was completed. 


coarse, gravelly material in front of the wall indicates 
the wall’s effectiveness in preventing the fine-grained 
eroded material from being carried out into the lake. 

Preliminary reports of model studies on various shapes 
of seawall faces (2) indicate that next to the concave 
or re-entrant type, the vertical face is the most effective 
of all in reducing overtopping and wave runup. With 
vertical-face seawalls, reflection of waves and erosion 
of the beach in front of the seawall are at a maximum. 
Model studies (3) have indicated that the depletion of 
the beach probably ceases at a level of about one wave 
height below low water. Therefore, sheetpiling should 
be used at the toe of all vertical-face seawalls to pro- 
tect them from undermining and eventual damage to 
or loss of the complete structure (4). 

A variation of the vertical-face seawall is the stepped 
type, which presents easy access to the beach and 
breaks up the backwash, thereby reducing erosion of 
the beach in front of the structure. The stepped faces are 
subjected to wave pressures in increments and there- 
fore can be of lighter construction than other types of 
seawalls, which receive the full force at one time. As a 
safety measure, a sheetpile cutoff wall is placed at the 
toe to prevent damage to the structure should erosion 
of the beach prove to be greater than expected. 

Approximately 35 miles of stepped-face seawall sim- 
ilar to that shown in the photograph below has been 
built in Hancock and Harrison counties, Miss. These 


Stepped wall protecting boulevard was built in Hancock County, Miss. 


® 


seawalls, which vary from 3 to 10 steps in height, have 
given more than 25 years of excellent service. 

The photograph to the right shows another 25-year- 
old stepped seawall in excellent condition on Lake 
Pontchartrain at New Orleans. A typical section of this 
wall is shown in Fig. 8. 


3 Batter piles 


each40'section 


18"105" 


Fig. 8. Section of stepped seawall at Lake Pontchartrain, New Or- 


leans, La. 


H. D. Shaw, engineer, Gulfport, Miss. 


, 


a 


Stepped seawall on Lake Pontchar- 
train, New Orleans, La., was de- 
signed by John Klorer, chief engi- 
neer, Board of Levee Commissioners. 


Stepped seawall was built at Mil- 
waukee, Wis., in 1953. 


Ilz 


Fig. 9. Stepped seawall along Lincoln Memorial Drive, Milwaukee. 


5 Risers at 
u" 


The stepped seawall shown in the photograph above 
was constructed in 1953 by the Milwaukee County 
Regional Planning Department to protect a portion of 
its Lake Michigan shoreline. The cross-section of this 
seawall is shown in Fig. 9. Air-entraining portland ce- 
ment was used in the upper portions where exposure 
to severe freezing and thawing could be expected. 

Seawalls with concave or re-entrant faces are the most 


CTATANG. A). Lake 
S 


23 


Concave seawall at Galveston, Texas, has protected the city several 
times against waves as severe as those that greatly damaged it in 
1900. Construction began in 1902. 


Construction joint 
( finish rough) 


Pp * weep holes 


Backfill 
material 


655" 


Fig. 11. Section of Bayshore seawall, Tampa, Fla. 


effective in reducing wave overtopping to a minimum. 
Like other seawalls, these types require sheetpiling at 
the toe. The concave-face seawall at Galveston, Texas, 
has proved its value so well that it has been lengthened 
five times since 1902. (See Fig. 10.) 

The Bayshore seawall at Tampa, Fla., is still as beau- 
tiful as it was when it was built 18 years ago. This 
re-entrant-face wall protects the shore from the tropi- 
cal storms that sweep in with hurricane force from the 
south. Fig. 11 illustrates details of the design. In addi- 


24 


aig? EE 
leet 
BERTH ES 


Tampa, Fla., Bayshore seawall, was built in 1938. Designed by F. H. 
Horton, Tampa, Fla. 


tion to its pleasing appearance, other notable features 
of the wall are the economy of material and the low 
construction cost, due in part to simplicity of form 
construction. 

Extensive damage caused by stormwater flooding 
valuable government property led to the construction 
in 1934 of a massive gravity seawall extending 9,000 ft. 
along Chesapeake Bay at Fort Monroe, Va. Fig. 12 
shows a typical cross-section. The slight overhang is 
intended to throw back the spray. 


Gn 25+0" 


Concrete curb 
pCO. «14.08 


S) 
mi Se 
PERS 


Natural ground line 


Fig. 12. Section of seawall at Fort Monroe, Va. 


Seawall fronting on Chesapeake Bay at Fort Monroe, 
Va., was designed and built by Department of the 
Army, Corps of Engineers. 


Although the wall faces the Bay, storm waves sweep- 
ing in from the ocean must be resisted. Due to uncer- 
tainty regarding the size of waves to which it might be 
exposed, the structure was designed to withstand the 
force of waves overtopping the wall by 10 ft. 

The seawall at Hampton Beach, N.H., (Fig. 13) 
was constructed in 1934. It is subjected to waves strik- 
ing it directly and obliquely, depending on the direction 
of the wind. The active littoral current along the shore 
added to the problem of protection. The wall has a 
pronounced overhang to prevent spray from dashing 
onto the road, and it is built on a 12-in. thick reinforced 
concrete slab instead of on piles. . 

The Ocean Beach Esplanade wall in San Francisco 
is an outstanding example of a combination of stepped 
and curved types. Built in 1915 to protect the scenic 
highway that parallels Ocean Beach near the entrance 


Foundation piles 


EL. 13.0 El. 13.177 


3+6" 3+6" \+6" tel"\ 7+4" 


15*0 Sheetpiling 


of San Francisco Bay, the wall was extended in 1921 
and in 1928 (see photograph on page 27). 

Careful study was given to the problem of incorporat- 
ing safety features into the design. Since foundation 
material consisted of sand to a depth of approximately 
200 ft., it was necessary to confine and protect the ma- 
terial under the wall with concrete sheetpiling. Im- 
mediately under the heavy toe of the seawall a cutoff 
wall of interlocking reinforced concrete sheetpiles was 
driven to a depth of 20 ft. Crosswalls of a similar type 
are located every 150 ft. along the seawall to prevent 
progressive destruction in case one section should be 
undermined. The back of the wall is supported and 
anchored by concrete pedestal piles spaced 10 ft. apart. 
Solidly compacted clay was placed above the sand 


E1485 


CA 


A DETAIL OF 
Gravel EXPANSION JOINT 
18*O" 
Batter 
Att: Stones weigh 2 to 5 tons 


Fig. 13. Seawall at Hampton Beach, N.H. Designed and constructed 
under direction of New Hampshire Highway Department. 


25 


2'6" 3:3" 


Top of wall 


H-beams 20°0"o.c. 20*0" 


Promenade 


Scupper 
(pete ae sea lst 


NTE square pedestal pile r 


24°6" long ——F 
| 


Extreme high tide pert ue ik't A r 


I-O''concrete 


= 
l wall between | 


BALES 
b sheetpilling | 


Mean Seq | level Sa 


| 8 'underdrain 
| and outlet 
Cross walls are to parle Splolan, at C | : | 
this line. (a | i 
| 
| 
| 
aS | 
nea 
iA 


wy 


| and beam i 


Two bulb Sica) aa replace 
pedestal pile when al pile. ‘ 
conflict with pedestal pile. ae 


Interlocking 
sheet piles 
Sella Balexorll PSs --4 | | 
SECTION C-C a 
ae 
Loses 


Fig. 14. Details of San Francisco Esplanade seawall. 


foundation to prevent removal of sand by seepage in 
case cracks should develop in the stepped section. 
Fig. 14 shows details of the wall. 

The unusual seawall shown in the photograph on 
page 30 was constructed in 1929 as part of a great sea- 


Bulkhead of precast concrete sheetpiles was built by the city of Daytona 
Beach, Fla. The precast concrete sheetpiles were 8 in. by 30 in. and 
15 ft. 3 in. long. A concrete cap 15 in. wide by 12 in. deep is provided 
on the top of the sheetpiling. Designed by C. H. Moneypenny, engineer, 
of Daytona Beach. 


This typical 30-year-old bulkhead at Jacksonville, Fla., consists of 
precast slabs held by king piles. Encased tierods anchor the wall to the 
backfill. Designed and built by Shore-Line Builders, Inc., Jacksonville. 


The San Francisco Esplanade seawall extension is shown after completion in 1928. 


wall and boulevard system along the Mississippi Gulf 
Coast. 

This seawall consists of a sloping convex slab with toe 
protected by interlocking concrete sheetpiling. This 
type of seawall is less effective against wave runup 
than any other type and, therefore, it requires addi- 
tional height to prevent overtopping. Its use should be 
restricted to areas where overtopping is not a problem 
or where, for other reasons, other shapes cannot be used. 

Bulkheads are similar in function to seawalls in that 


qit 


. c's \ " 
4 expansion joint 0 a 


C7 


SECTION AT JOINT 


4"Flap valve 
H.Water El. 4.60 


IN SNA TANS BALIBRSSS INNS y 


EE LAPEER EAA 
g*3" 


Original beach line 


11.40' 


3"T.& G. sheetpiling 340" long. 


Fig. 15. Section of revetment at Pioneer Point, Md. 


both separate land from water areas. A bulkhead’s pri- 
mary purpose is to resist earth pressures, whereas a 
seawall is designed to prevent erosion and other dam- 
age due to wave action. There is no sharp line of de- 
marcation between the two types, and considerable 
overlapping occurs. Since resistance to wave action is 
secondary, bulkheads may be built lighter than sea- 
walls. Consequently, they are generally of precast con- 
crete sheetpiles or crib construction. Sheetpiles may 
or may not require tiebacks. 


Revetment at Pioneer Point, Chesapeake Bay, Md. 


| Construction : joi 


o" 


J " ‘a dummy joints 


x) 
9° t 
io 8 Curtain wall 
= _ (at_ends) 
Het 
' |! ~— Existing sidewalk 
yt PLAN 
gtg" gtg" Varies 

ee i 64 Normal Piper ft. 
FO Fr SRR a 


Dummy joint 
sal mid point 


: Mean sea level 


Original seawall 
washed out 


ELEVATION 


Fig. 16. Details of design for revetment at Key West, Fla. 


Revetments, like seawalls, protect both the land and 
improvements from damage by waves. However, unlike 
seawalls, revetments are not designed as retaining walls 
but are designed to rest upon and be supported by the 
earth behind them. They are sloping structures, usually 
placed as near to the angle of repose of the supporting 
materials as feasible. This sloping face facilitates rather 
than hinders wave runup and for this reason they are 
among the most susceptible to overtopping of all on- 
shore structures. 

Although the shoreline of Chesapeake Bay in the vi- 
cinity of Pioneer Point is subjected to comparatively 
moderate waves and currents, the presence of easily 
erosible beach material necessitated the construction 
of an inexpensive type of concrete revetment (see 
photograph on preceding page). Fig. 15 illustrates 
the design adopted. The revetment is essentially a pave- 
ment slab cast in 12%-ft. lengths and reinforced with 
galvanized metal mesh with dowels across joints. The 
lower portion of the slab is stepped to reduce wave 


28 


action and the toe is protected by sheetpiling driven 
into stiff clay foundation. Weep-holes at 200-ft. inter- 
vals permit drainage from 4-in. tile pipe at the rear 
of the wall. 

The concrete revetment protecting Roosevelt Boule- 
vard at Key West, Fla., was built in 1951 by the Florida 
State Road Department to replace the original seawall, 
which was on a 1-to-1 slope. The sidewalk and pave- 
ment behind this revetment, as shown in Fig. 16, pre- 
vent damaging erosion from wave overtopping. 


Durability of Structures 


The performance of shore-protection structures de- 
pends on the integrity of their design and the durability 
of their constituent parts. Structural stability against 
the direct battering of storm waves and against the 
effect of wave and current action on foundation mate- 
rials is essential, but the importance of durability of the 
structural materials should not be ignored. Since shore- 
protection structures often are exposed to the action of 
seawater, as well as to freezing and thawing, wetting 
and drying, and wave action, it is mandatory that the 
materials used in their construction be of the highest 
quality. 

Concrete that is properly proportioned, mixed and 
placed is one of the most durable materials available 
for shore protection. Not only the concrete structures 
illustrated in this booklet but countless others in service 
all over the world are testimonials to concrete’s sat- 
isfactory performance with little or no maintenance. 
However, because of the severity of exposure it is essen- 
tial that the concrete be of the highest quality. Also, 
certain other features of design and construction, in 
addition to durable materials and structural stability, 
should be carefully considered if long-lasting structures _ 
are to be obtained. ie 

One of the most important of these is the protection : | 
of reinforcement against the corrosive action of salts 
in seawater. It is essential that the reinforcement b 
placed farther from the exposed face of a concr 
shore-protection structure than from the exposed f: 
of a similar land structure. It is also important to p 
vide an impervious concrete to help keep the salt we 
away from the reinforcement. 

Another vulnerable point of attack in shore-protect 
structures is the horizontal construction joint. § 
joints should be avoided whenever possible. When th 
must be made, care should be taken to construct th 
properly. The durability of construction joints is affe 
by the quality of the concrete immediately below 
joint and the care taken in preparation of the jo 
surface before fresh concrete is placed for the adjoini 
upper lift. A number of methods can be employed thai 
will produce a satisfactory joint. 

One of the best methods to assure good bonding and 


watertightness is wet sandblasting and washing imme- 
diately before placement of the fresh concrete. A pre- 
requisite, of course, is that the concrete in the upper 
portion of the lower lift be placed at the lowest slump 
consistent with proper placement and consolidation. It 
is particularly important to avoid wet mixes that might 
cause segregation or bleeding, which would result in 
a layer of laitance and thus make cleanup of the joint 
more difficult. The concrete should be left relatively 
even. Sandblasting should be done before the side forms 
are erected. However, it should be limited to removal 
of laitance only since further cutting and roughening of 
the joint will not insure a good joint. Just prior to place- 
ment of fresh concrete the joints should be thoroughly 
cleaned with an air-water jet, after which a layer of 
cement mortar should be spread evenly over the joint 
surface. 

To obtain concrete that meets all the requirements 
of durability, strength and impermeability and yet has a 
consistency suitable for construction of shore-protection 
structures, the following recommendations should be 
followed: 


1. Well-graded aggregates of known soundness and 
durability meeting current ASTM Specifications for 
Concrete Aggregates: C33 should be used. The max- 
imum size of the coarse aggregates should be as large 


as possible but not larger than one-sixth the smallest 
dimension of the forms or three-fourths of the minimum 
clear opening between reinforcing bars. 

2. The water-cement ratio should be not more than 
5% gal. of water per sack of portland cement, including 
water entering the mix as free moisture on the aggre- 
gates. The mixture should contain not less than 7 sacks 
of cement per cu.yd. Proportions of fine to coarse aggre- 
gate should be adjusted so that a workable mixture is 
produced without the addition of water. 

3. All steel, including main reinforcement, stirrups 
and chairs, should be at least 3 in. from the exposed 
faces and 4 in. from corners. 


Gr pone H.W.O.S.T. 7 


ra 6 


Original beach line 


SECTION ee 


Fig. 17. Ross Bay, B.C., Canada. 


Veteran seawall at Ross Bay, Victoria, B.C., Canada, has been exposed to heavy wave action and to pounding by heavy logs and other waterborne 
debris for more than 50 years. Although slightly scarred from severe service, the wall is in sound condition and will serve the community for many 
years to come. 


Unusual convex seawall in Jackson County, Miss., has resisted abrasion 
so well for 26 years of exposure that form marks are still visible. 
Designed by F. H. McGowen, Ocean Springs, Miss. 


4. Air-entrained concrete should be used for all shore- 
protection structures. In addition to protecting concrete 
from the damaging effects of freezing and thawing, air- 
entrainment also helps to make concrete more durable 
by reducing segregation and bleeding and by improv- 
ing workability. The total air content required in the 
mix for durability depends on a number of factors. For 
average mixes of 5 to 5% gal. of water per sack of cement 
and for coarse aggregates of 14- to 2-in. maximum size, 
4 to 7 per cent entrained air is suggested. For concrete 
exposed to seawater improved sulphate resistance may 
be obtained by using Type II portland cement.* 

5. Proper placing of concrete in the forms cannot be 
overemphasized. Every precaution should be taken to 
prevent segregation. 


30 


SOO anno sms, 90" 
Sidewalk 


Roadway 


Tar joint 


Drains 


Tar joint 


Concrete sheet piling 


Fig. 18. Convex seawall at Jackson County, Miss. 


6. Concrete should be cured under favorable condi- 
tions at temperatures of 50 deg. F. or more. In general, 
it should be kept moist for at least 3 days where tem- 
peratures are 70 deg. F. or above, or at least 5 days at 
temperatures of 50 deg. F. 


More complete information on methods of producing 
quality concrete is found in the publications Design 
and Control of Concrete Mixtures, Concrete in Sea 
Water and Watertight Concrete, available free on re- 
quest from the Portland Cement Association. Distribu- 
tion is made only in the United States and Canada. 


“ Type II modified portland cement, complying with ASTM 
Standard Specification: C150, is intended for use where sulphate 
concentrations are higher than normal. 


Shore Protection Planning and Design. Technical Re- 
port No. 4, Beach Erosion Board, 5202 Little Falls 
Road, N.W., Washington 16, D.C., 1954. (For sale by 
the Superintendent of Documents, U.S. Government 
Printing Office, Washington 25, D.C.) 


. Dunham, James W., “Refraction and Diffraction Dia- 


grams.” Proceedings of First Conference on Coastal 
Engineering, Council on Wave Research, 244 Hesse 
Hall, Berkeley, Calif., 1951, pages 33-49. 


. Johnson, J. W., and Isaacs, J. D., “Action and Effect of 


Waves.” Western Construction, Vol. 23, No. 4, April 
1948, pages 97-102, 116. 


. Johnson, J. W., “Generalized Wave Diffraction Dia- 


grams. Proceedings of Second Conference on Coastal 
Engineering, Council on Wave Research, 1952, pages 
6-23. 


. Kaplan, Kenneth, Analysis of Moving Fetches for Wave 


Forecasting. Technical Memorandum No. 35, Beach 
Erosion Board, 1953. 


. Bretschneider, C. L., “Revised Wave Forecasting Re- 


lationships.” Proceedings of Second Conference on 
Coastal Engineering, Council on Wave Research, 1952, 
pages 1-5. 


. Neumann, G., On Ocean Wave Spectra and a New 


Method of Forecasting Wind-Generated Sea. Technical 
Memorandum No. 43, Beach Erosion Board, 1953. 


. Wiegel, R. L., and Johnson, J. W., “Elements of Wave 


Theory.” Proceedings of First Conference on Coastal 
Engineering, Council on Wave Research, 1951, pages 
5-21. 


. Russell, R. C. H., and Inglis, Sir Claude, “The Influence 


of a Vertical Wall on a Beach in Front of It.” Proceed- 
ings, Minnesota International Hydraulics Convention. 
Minneapolis, Minn., 1953, pages 221-226. 


. Saville, Thorndike, Jr., and Caldwell, Joseph M., 


“Experimental Study of Wave Overtopping on Shore 
Structures.” Proceedings, Minnesota International Hy- 
draulics Convention, Minneapolis, Minn., 1953, pages 
261-269. 


Lis 


13. 


14. 


15. 


Escoffier, Francis F, “Design and Performance of Sea 
Walls in Mississippi Sound.” Proceedings of Second 
Conference on Coastal Engineering, Council on Wave 
Research, 1952, pages 257-267. 


. Danel, Pierre, “Tetrapods.” Proceedings of Fourth Con- 


ference on Coastal Engineering, Council on Wave 
Research, 1954, pages 390-398. 

Gesler, Colonel E. E., “Economics of Coastal Struc- 
tures.” Proceedings of Second Conference on Coastal 
Engineering, Council on Wave Research, 1952, pages 
236-242. ; 
Elliott, Dabney O., “The Beach Erosion Board.” Pro- 
ceedings of First Conference on Coastal Engineering, 
Council on Wave Research, 1951, pages 126-131. 
Casey, Thomas B., “Erosion Along the Illinois Shore 


_ of Lake Michigan.” Proceedings of Second Conference 


16. 


SES 


18. 


19. 


on Coastal Engineering, Council on Wave Research, 
1952, pages 166-176. 

Wiegel, Robert L., Waves, Tides, Currents and Beaches: 
Glossary of Terms and List of Standard Symbols. Coun- 
cil on Wave Research, 1953. 

Eaton, Richard O., “Littoral Processes on Sandy Coasts.” 
Proceedings of First Conference on Coastal Engineer- 
ing, Council on Wave Research, 1951, pages 140-154. 
Putman, J. A., Munk, W. H., and Traylor, M. A., “The 
Predication of Longshore Currents.” American Geophys- 
ical Union, Vol. 30, No. 3, June 1949, pages 337-345. 
Caldwell, Joseph M., “Research Activities of the Beach 
Erosion Board.” Proceedings of Second Conference on 
Coastal Engineering, Council on Wave Research, 1952, 
pages 187-194. 

Davis, Albert B., Jr., “History of the Galveston Sea 
Wall.” Proceedings of Second Conference on Coastal 
Engineering, Council on Wave Research, 1952, pages 
268-280. 


. Information Circular on Cooperative Studies of Beach 


Erosion and Federal Participation in Construction of 
Protective Works. Beach Erosion Board, Washington, 
D.C., 1952. 


31 


Bibliography | 


Printed in U.S.A: 


were! ee. al eel 


ALS yy eT as Oh 


1 


HISTORY OF WATER CONTROL page 3 


STABILIZATION STRUCTURES page 9 


WATERSHED PROTECTION page 11 


FLOOD CONTROL page 14 


DAMS page 16 


CHANNEL IMPROVEMENTS page 24 


CONCRETE FOR WATER 
CONTROL STRUCTURES page 35 


Shasta Dam in California. 


Courtesy of Bureau of Reclamation 


Copyright 1959 by Portland Cement Association 


z 


HISTORY OF WATER CONTROL 


Water can be either man’s best friend or his worst 
enemy. Controlled, water serves the increasing needs 
of civilization in greater measure than any other 
natural resource; uncontrolled, it can create havoc. 

The health and economic well-being of every com- 
munity and of the nation as a whole depend on an 
adequate and satisfactory supply of water for munic- 
ipal, industrial, agricultural and other uses. 

Water use by municipalities, industry and agricul- 
ture increased from 40 billion gallons daily in 1900 
to 260 billion gallons daily in 1955. This figure is con- 
servatively expected to exceed 450 billion gallons by 
1975. 

It is estimated that by 1975 the nation’s popula- 
tion will be more than 200 million, industrial pro- 
duction will double and irrigation will increase 40 
per cent. 

At present, the greatest use of fresh water is for 
irrigation. Although irrigation in the past has largely 
been confined to the 17 western states, more and 


Typical agricultural damage caused by a minor flood in a mid- 
western state. Such floods occur frequently in all parts of the 
country. Courtesy of Soil Conservation Service 


more acres in the other states are receiving supple- 
mental irrigation to increase crop yields. 

In the United States, there is an average of 30 in. 
of precipitation each year. Of this, approximately 
11 in. is evaporated from ground and water surfaces 
and 11 in. is transpired by plants, which leaves about 
8 in. of runoff and underflow. Frequent excessive 
precipitation within a short period of time results in 
high runoff which, if uncontrolled, may cause floods 
of disastrous proportions, creating great suffering 
and loss of life as well as staggering property dam- 
age. The economic loss chargeable to major floods 
each year runs into millions of dollars. 

As our nation becomes more thickly settled, the 
danger of flood and erosion damage increases. At one 
time the land area was, for the most part, covered with 
trees and grass. This vegetative cover helped protect 
the soil from erosion and aided in the percolation of 
surface water. Cultivation of the land and urban and 
industrial expansion have now eliminated much of 
the natural cover. This has aggravated soil erosion 
and reduced percolation of water into the soil. 

Adequate control measures must be undertaken, 
then, to minimize flood damages. These could in- 
volve clearing and maintaining river channels to 
ensure the passage of excessive runoff without ob- 
struction; construction of dikes and levees to confine 
the flow in water courses; protection of banks by 
revetments and floodwalls; and the construction of 
flood detention reservoirs. 


The shattered homes and personal property damage in this New 
England town are evidence of the huge economic loss caused by a 
major flood. United Press photograph 


This was all that remained of a 500-acre lake near Excelsior Springs, Mo., after a drought struck western and midwestern states in 1953. 


United Press photograph 


However, it would be a serious economic loss to 
undertake such flood control measures without, at 
the same time, considering means for alleviating 
water shortages and making provision for expected 
future water supply needs. Therefore, it is important 
to consider flood control in relation to a comprehen- 
sive program for the conservation of our entire water 
resources. 


FLOOD CONTROL 


Federal interest in flood control began with the 
Swamp Land Act of 1849 and 1850, which granted 
unsold swampland to Louisiana, Arkansas and other 
states containing such lands. These lands were to 
be sold by the states and the proceeds used for drain- 
age, reclamation and flood control projects. 

In 1874, Congress provided for a Commission of 
Engineers to investigate and report on a permanent 
plan for protecting that portion of the alluvial basin 
of the Mississippi River subject to inundation. The 
commission’s report suggested various methods of 
control and pointed out that the problem of success- 
fully controlling floods crosses over state lines. 

Congress established the Mississippi River Com- 
mission in 1879. At first, appropriations were only 
for navigation improvement and relief of flood suf- 
ferers, but starting in 1917, appropriations also were 
made for levees and other flood protection units in 
the lower Mississippi River Basin. 

In 1928 Congress took the first step toward modern 
flood control by directing the completion of studies 
for supplementing the levees in the lower Mississippi 
Basin with a system of tributary reservoirs. 


After the nationwide destructive floods of 1936, 
Congress passed the 1936 Flood Control Act. This 
Act, which authorized a broad flood control program, 
emphasized the concept of multiple-purpose reser- 
voirs. It also authorized the Department of Agricul- 
ture to undertake upstream flood prevention work on 
certain watershed projects. Subsequent Acts em- 
braced more fully the multiple-purpose concept. 


COMPREHENSIVE BASIN PLANNING 


The early programs of the Corps of Engineers con- 
sisted almost entirely of single-purpose projects for 
navigation and flood control. Under present author- 
ity, facilities for power, recreation, fish and wildlife, 
and irrigation may be included in Corps of Engineers’ 
projects where appropriate. The Corps may design 
flood control reservoirs to provide additional storage 
for local benefit if local interests pay the increased 
cost. 

The Bureau of Reclamation was created by Con- 
gress in 1902 primarily to construct irrigation facili- 
ties in the 17 western states. Where appropriate, 
however, the Bureau’s projects may also include fa- 
cilities for flood control, municipal and industrial 
water supply, power, and fish and wildlife develop- 
ment. 

In 1944, after submission of separate reports by 
the Corps of Engineers and the Bureau of Reclama- 
tion, Congress authorized construction of the Mis- 
souri River Project, which provided for the develop- 
ment of the water resources of the entire Missouri 
River Basin. This included the construction of multi- 
ple-purpose reservoirs for flood control, irrigation and 


oe 
de 
we 


oa 


Hungry Horse Dam, concrete arch structure in western Montana, in- 
cludes facilities for flood control, power generation and recreation. 
Courtesy of Bureau of Reclamation 


generation of hydroelectric power; conservation of 
water for navigation and water supply; recreation 
and wildlife; local flood protection works; and facili- 
ties for the irrigation of lands and related uses. Since 
authorization of the project, detailed planning has 
continued up to the present time under the sponsor- 
ship of the Missouri Basin Inter-Agency Committee, 
consisting of representatives of the participating fed- 
eral agencies and the 10 states of the basin. Most of 


Canyon Ferry Dam on the Missouri River about 17 miles east of Helena, Mont. 


the construction to implement this comprehensive 
plan is under the direction of the Corps of Engineers 
and the Bureau of Reclamation. 

The Flood Control Act of 1950 authorized the 
Corps of Engineers to undertake comprehensive sur- 
veys of the Arkansas-White-Red River Basins and 
of the New England-New York area. The Act pro- 
vided for the development of ‘‘comprehensive inte- 
grated plans of improvement for navigation, flood 
control, domestic and municipal water supplies, rec- 
lamation and irrigation, development and _utiliza- 
tion of hydro-electric power, conservation of soil, 
forest and fish and wildlife resources, and other bene- 
ficial development and utilization of water resources 
including such consideration of recreation uses, salin- 
ity and sediment control, and pollution abatement 
as may be provided for under Federal policies and 
procedures. .. .”” Other federal agencies were directed 
by the President to participate in these surveys under 
a committee arrangement, with the Corps of Engi- 
neers acting as chairman agency. The affected states, 
in each survey, were invited to become members of 
these committees. Throughout the study, the states 
participated actively with the federal agencies in de- 
velopment of the plans. 

The largest single water control problem in this 
country is in the lower Mississippi Valley. The 
Mississippi River and its tributaries drain 41 per cent 
of the area of the United States. Because of the size 
of this drainage area, control of the normal annual 
spring runoff is a major problem. When the runoff is 


, is a multiple-purpose dam for irrigation, flood control and 


power. This concrete gravity dam, 1,000 ft. long and 212 ft. high above bedrock, was completed in 1953. Courtesy of Bureau of Reclamation 


aah 


er i ey 


fa il” 


Fort Gibson Dam in eastern Oklahoma on the Grand River, a major tributary of the Arkansas River, combines flood control, power and 
recreational facilities. The concrete portion of this dam, completed in 1953, is a gravity structure 2,850 ft. long and 90 ft. high. 


Courtesy of Corps of Engineers 


increased by unusually long-continuing and wide- 
spread rainfall, devastation follows. Therefore, a plan 
of control is essential. 

Such a plan, based on sound engineering studies, 
has been developed and is now partially in effect; 
more work is being completed every year. The plan 
is designed to control the largest flood expected to 
occur in the valley. It includes reservoirs on tributary 
streams, levees and floodwalls, cutoffs and floodways. 

Flood control work in small watersheds began in 
1947. In 1953 Congress passed the Pilot Watershed 
Act, thereby authorizing flood control work in 60 
watersheds throughout the United States. An objec- 
tive of this Act was to demonstrate the effectiveness 
of coordinating soil and water conservation practices 
on individual tracts of land with flood control struc- 
tures on a watershed basis. The Watershed Protec- 
tion and Flood Prevention Acts of 1954 and 1956 
modified the previous legislation by detailing the pro- 
cedures and conditions under which such projects are 
to be developed. The Department of Agriculture was 
authorized to provide some financial aid and assist 
local governments in planning the development of 
small watersheds. 

Another federal agency with an interest in water 
control and utilization is the Tennessee Valley 
Authority, which was created in 1933. This is an 
independent agency within the executive branch of 
the government. It has responsibility for the full 
development of the Tennessee River for flood control, 
navigation, power and other purposes. 


The activities of other federal agencies concerned 
with water resources, such as the Public Health Sery- 
ice, Fish and Wildlife Service, and Geological Survey, 
involve research and technical assistance with respect 
to water supply and waste disposal, and collection 
and publication of basic data. These agencies partici- 
pate with or assist the major construction agencies 
in the investigation of river basin development proj- 
ects or programs. 


Hiwassee Dam on the Hiwassee River, about 75 miles southwest of 
Asheville, N.C., was constructed by the Tennessee Valley Authority. 
This concrete gravity structure, 300 ft. high, was completed in 1940. 


The activities of states and local agencies in the 
control of floods and conservation of our water re- 
sources have been spurred by water shortages 
throughout the nation and disastrous floods in many 
areas. 

A number of states have enacted legislation 
authorizing the formation of flood control districts. 
One of the earliest of these was Ohio, where a 
Conservancy Act was passed in 1914. Under this Act, 
13 flood control districts were formed. The largest 
and most active of these were the Miami Conservancy 
District and the Muskingum Conservancy District. 
Under their sponsorship, flood control projects 
were initiated and constructed for the Miami and 
Muskingum River basins respectively. 

The proposed California Water Plan, under the 
State Department of Water Resources, is intended to 
be used as a guide for future water development in 
the state. This plan includes over 700 new reservoirs, 
as well as conduits, control works and other facilities, 
and is estimated to cost more than $12 billion. 

California also has active flood control districts 
that cooperate with the Corps of Engineers and other 
agencies in the planning and construction of flood 
control projects. 

Los Angeles and its suburbs are situated on a fer- 
tile plain, most of which is drained by the Los Angeles 


River, the San Gabriel River, Ballona Creek and 
their tributaries. An unfavorable combination of 
topography, high intensity of rainfall, and density 
of population required a wide variety of design and 
construction practices to provide adequate flood pro- 
tection. The combined drainage area totals only 1,525 
Square miles, being about 48 miles north to south and 
64 miles east to west. Elevations range from sea level 
at Los Angeles harbor to 10,080 ft. at the peak of 
Mount San Antonio. About half the drainage area 
is Classified as mountainous and one-third is in a 
national forest. 

Flood and erosion control work in this area is being 
carried on by the Los Angeles County Flood Control 
District, the Corps of Engineers, the Soil Conserva- 
tion Service and the Forest Service. In the foothill 
areas, dams and debris basins are being built to store 
floodwaters and to trap water-borne debris. These 
Structures are of earth and rock, concrete, soil-ce- 
ment, and precast concrete crib* construction. Con- 
crete-lined channels are used to confine the outflow 
from many of these retarding basins. Below the foot- 
hills and on the coastal plain, channels have been en- 
larged, straightened, provided with bank protection, 


*See Concrete Crib Retaining Walls, available on request 
to the Portland Cement Association only in the United 
States and Canada. 


Dover Dam on the Tuscarawas River, near Dover, Ohio, is a flood control structure built in 1935 by the Muskingum Conservancy District. 


Courtesy of Ohio Farm Bureau News 


Hansen Flood Control Dam and Tujunga Wash channel were con- 
structed by the Corps of Engineers in cooperation with the Los 
Angeles County Flood Control District. This concrete-lined channel 
carries floodwater through highly developed urban areas without 
damage. Courtesy of Corps of Engineers 


or completely enclosed in concrete. Several large 
dams have been constructed to form floodwater-re- 
tarding basins. These serve one or more of the follow- 
ing purposes: catching debris carried by the inflow; 
reducing the outflow to the channel capacity; and 
diverting the water into spreading grounds through 
which it percolates into subsurface groundwater 
storage reservoirs rather than wasting into the ocean. 


One of several soil-cement check dams built for the Coon Canyon 
Project in Los Angeles County, Calif., by the U.S. Forest Service. 
This dam was built in 1950. 


In 1957, the Texas legislature voted to spend $200 
million for a long-range water conservation program. 
This money will provide loans to cities, towns and 
water districts for planning and constructing water 
conservation facilities. 

The flood control program of the Central and 
Southern Florida Flood Control District is a good 
example of a comprehensive water control program 
providing for flood control, navigation, drainage, 
water supply, soil conservation and wildlife conserva- 
tion. This program entails close cooperation among 
local, state and federal agencies in planning, finane- 
ing, constructing and operating the project. 

Flood control should not be considered as a single- 
purpose function; many flood control structures per- 
form several services. For example, reservoirs for flood 
control may also be used as water storage reservoirs; 
dams may have multiple purposes; any structure 
used for retarding the flow of water helps to replenish 
the underground water supply. — 

A comprehensive plan for water control should serve 
as a guide for the construction of works for the con- 
servation, control, protection and distribution of all 
of the water resources of a river basin. Such a plan 
should provide for the prevention of land erosion, the 
control of floods, and the use of water for irrigation, 
municipal and industrial needs, fish, wildlife and ree- 
reational purposes, salinity control and waste dis- 
posal. Integral parts of the plan can be completed as 
they become necessary or desirable. It is not essen- 
tial that all of them be developed at one time or by 
any particular group or agency. 


One of nine precast concrete crib dams built by the Forest Service 
in 1956 in Cook's Canyon, Los Angeles County, for grade stabiliza- 


tion. Courtesy of Forest Service 


STABILIZATION STRUCTURES 


Land conservation practices are based largely on 
the application of sound agronomic and engineering 
practices to the farming program. Minor structures 
are frequently required to control the disposal of 
water from terrace outlets. They may also be required 
for gully control and to create farm ponds. 


Terrace channel on an lowa farm after a heavy rain. 
Courtesy of Soil Conservation Service 


DISPOSAL OF WATER FROM TERRACES 


Terracing is one of the most effective methods of 
controlling water on sloping cultivated lands. Terrace 
channels usually are constructed either to a level 
grade, following the contours, or on a slight grade 
across contours. The former are used in dry or semi- 
arid areas where it is desirable to retain all precipita- 
tion for absorption by the soil; the latter are used in 
humid areas where it is necessary to dispose of excess 
precipitation. In this case, drainage channels must 
be provided to dispose of the excess water. To prevent 


This series of concrete check dams will prevent gully formation. 


excessive soil erosion or gully formation in these 
channels it is frequently necessary to construct sta- 
bilizing structures. Usually this can be accomplished 
by constructing a series of check dams that overlap 
each other vertically and thus prevent bottom-scour. 
In the case of very steep land it is sometimes neces- 
sary to use vertical drops or chutes to avoid excessive 
grades in the channel. In all cases concrete aprons 
should be installed on the lower side of such struc- 
tures to dissipate the energy of the rapidly flowing 
water and prevent scour. Wingwalls of all check dams 
and other structures should be extended far enough 
into the banks to prevent water from bypassing the 
structures (see Fig. 1). 


Fig. 1. lsometric view of a check dam. 


GULLY CONTROL 


Progressive gullying is caused by the uncontrolled 
flow of water in erodible channels. A small gully, if 
uncontrolled, will nearly always grow into a large 
one. Control of the gully is possible through the in- 
stallation of check dams similar to those used in ter- 
race channels. Such dams serve a twofold purpose: 
further growth of the gully is prevented, and soil is 
deposited behind them, permitting the growth of 
vegetation. They may be of the gravity or the canti- 
lever type. In either case they should include wing- 
walls extending into the gully sides, aprons for dis- 
sipation of energy and foundations deep enough not 
to be affected by frost heave. To produce a minimum 
depth of flow through the weir notch, weirs should be 
as large as practicable. (For more detailed informa- 
tion on the construction of concrete checks and flumes 
see the Portland Cement Association publications, 
Concrete Soil-Saving Structures and Save Your Soil 
With Concrete.*) However, check dams higher than 
about 10 ft. require careful design and construction, 
and should not be built without the aid of a qualified 
engineer. 


*Available only in the United States and Canada. 


An unprotected drain outlet resulted in heavy erosion until concrete headwall and apron were constructed. Further gully formation was 


prevented. Courtesy of Soil Conservation Service 


FARM PONDS 


A farm pond usually is designed to store water 
for stock and irrigation. It may provide rec- 
reational benefits and water for domestic use and 
sometimes serves to store floodwaters temporarily and 
retain sediment that otherwise would cause pollution 
downstream. 

Concrete and earth dams have been used to create 
ponds. The most suitable type of dam will be deter- 
mined by topography, soil and other site conditions. 
Where concrete is used, a spillway may be built as 
part of the dam. For earth or rockfill dams the spill- 
way is usually constructed in undisturbed soil to one 


This check dam near San Fernando, Calif., was built of concrete 
masonry units. Courtesy of Soil Conservation Service 


10 


side of the dam; it should be lined with concrete or 
soil-cement. 

In some soils it may be necessary to line the sides 
and bottom of the pond to prevent excessive seepage. 
Concrete or soil-cement may be used for this purpose. 
(For further information on these subjects see the 
Portland Cement Association publications, Concrete- 
Lined Reservoirs and Soil-Cement for Paving Slopes 
and Lining Ditches.*) 

Before a farm pond is constructed, its possible effect 
on downstream flows and water rights should be care- 
fully investigated and evaluated. j 


*Available only in the United States and Canada. 


This farm pond in Decatur County, Ind., has a concrete spillway” 
protect earth dam against failure. 


Typical of small watershed programs is the one on 
Sandstone Creek in western Oklahoma, which was 
completed in 1954. Before development of the project 
this predominantly agricultural watershed of some 
65,000 acres was subjected to an average of nine 
floods a year. The construction of a system of 24 
floodwater-retarding structures has prevented flood- 
flows over the bottom lands, which previously sus- 
tained 75 per cent of the flood damage. Other work 
in the watershed has included conservation measures 
by individual landowners, the construction of drop- 
inlet structures for grade stabilization and sediment 
control, and channel improvements. All completed 
works are maintained by local beneficiaries. 

Pollution abatement, drainage, irrigation and water 
storage facilities should also be included in watershed 
planning where appropriate. 

The major structure in a watershed development 
program is the floodwater-retarding dam (see Fig. 2). 
Such a dam usually has three outlets for the passage 
of water: 

1. An ungated outlet or drawdown tube for the 
passage of normal flows and the gradual release 
of floodwater held in the pool. 

2. A drain, equipped with gate valve or similar 
control, for occasional draining of the ‘‘dead- 
storage’’ pool. 

3. An uncontrolled spillway for flows in excess of 
the discharge capacity of the outlet conduit and 
the surcharge storage capacity of the reservoir. 

The dam usually is designed to retard the maxi- 
mum runoff expected once in 25 years, and to release 
it gradually through the ungated outlet, whose dis- 
charge is limited to the capacity of the channel below 
the dam. Such a design gives a high degree of pro- 
tection from most flood damage to the bottom lands 
immediately below the structure, since the majority 
of such damage results from the smaller storms that 
occur more frequently than once in 25 years. 


WATERSHED PROTECTION 


Watershed protection includes practices authorized 
under the Watershed Protection and Flood Preven- 
tion Act, passed by Congress in 1954. Soil stabiliza- 
tion, discussed in the previous chapter, is included in 
such work. But when exceptionally heavy rainstorms 
sweep over a watershed, runoff may be great even 
from well-managed farm and ranch land. This is es- 
pecially true if the heavy rains occur when the soil 
is frozen or already saturated. The runoff resulting 
from such a combination of circumstances can be 
controlled by retarding dams, floodwater diversion 
channels, stream channel improvements, levees and 
dikes. 


Reinforced concrete drop structure for grade control on Sandstone 
Creek, Washita River watershed, Okla. 


Courtesy of Soil Conservation Service 


90' 10' 46' 64' 8 54' 
Probable 
14" _ | embankment 
settlement 
3 
~ 2k 
—S 


Gated drain 48 


riginal groundline 


a ee Original gull 
——————_F——————F EES Tee, ES |e Ee | | r Botan ary 
Concrete cradle Collars Pi ee Collar ceo Endsill 


Culvert pipe Expansion joint 


Fig. 2. Cross-section of a typical floodwater-retarding dam. 


11 


Runoff from major storms—those greater than 
would be expected about every 25 years—would 
usually result in discharges, because of higher heads 
on the inlet, in excess of the downstream channel 
capacity. Such runoff might be expected to cause 
some damage to adjacent land. 

The spillway is usually designed to pass flows 
expected to occur once in 100 years. The height of 
the dam should be such that the maximum probable 
flood would pass through the spillway without over- 
topping the dam. This, of course, is more critical 
with earth or rockfill dams than with concrete dams. 
Sustained flow through an unlined spillway of an earth 
dam could cause damaging erosion and possible fail- 
ure of the dam itself, with disastrous results down- 
stream. Therefore, consideration should be given to 
lining the spillway with concrete or soil-cement. 

The foregoing discussion should serve to emphasize 
the need for hydrologic studies as a necessary part 
of dam design to determine flows to be expected at 
25- and 100-year intervals. Such information is of 
great importance in establishing the maximum height 
of dam and reservoir storage capacity, the required 
outlet capacity, and the spillway characteristics. 
These data may be developed from an analysis of 
steamflow records, if such are available, or from pre- 
cipitation data from observation stations in the 
drainage area for the dam. Detailed information on 
hydrologic analysis may be found in one of the many 
reliable books on the subject. 

The drawdown tube and drain through the dam are 
often combined into one conduit with a low gated 
inlet and a higher uncontrolled drop inlet. It is de- 
signed as any conduit under a fill. Concrete pipe and 
cast-in-place concrete, because of their strength, dura- 
bility, economy and excellent hydraulic properties, 


are commonly used for such conduits. For convenient 
inspection and maintenance it is desirable to use at 
least a 21-in. diameter conduit. 

The ungated entrance to the drawdown tube is 
usually a drop inlet, but sometimes a hood inlet is 
used to provide increased hydraulic efficiency, simply 
and economically. The inlet is formed by cutting the 
pipe at an angle, with the long side placed on top. 
(See Fig. 3.) This long side forms a hood over the pipe 
entrance; hence the name ‘“‘hood-inlet.”’ A vortex- 
preventing vane is placed on top of the pipe, along 
the centerline. An area around the inlet should be 
paved to prevent scour. 


Vortex -preventing vane 


k—alternate vortex- 
| preventing vane positic 


2D 


Ala 


SIDE ELEVATION 


Fig. 3. Plan and elevation of hood inlet. 


Typical installations of outlet conduits through floodwater-retarding structures. Left—Reinforced concrete pipe conduit on Clear Fork, Trinity 
River watershed, near Weatherford, Texas. Right—Cast-in-place concrete conduit on Hunters Run watershed, Fairfield County, Ohio. Note 
anti-seep collars on both. Courtesy of Soil Conservation Service 


Junction of the reinforced-concrete-lined Cebada Channel (right) 
with the Purisima Channel (left). Santa Ynez River Flood Prevention 
Project, near Lompoc, Calif. 

Courtesy of Soil Conservation Service 


Scientific land management practices can protect 
agricultural, residential and industrial land within a 
watershed against damaging erosion, but some water- 
sheds include large areas of undeveloped land that 
cannot be so protected. If the resulting sediment were 
permitted to flow downstream, channels would soon 
become clogged and their capacity would be reduced. 
This would increase the frequency and severity of 
overbank flooding. To protect the downstream 
channels and floodplain lands, floodwater-retarding 
structures should be designed with provisions for ad- 
equate sediment storage capacity below the lowest 
ungated outlet. 

Channel improvements in small watersheds gen- 
erally consist of deepening, widening or lining chan- 
nels to increase their capacities. The construction of 
supplementary levees is sometimes necessary. Flood- 
ways and floodwater diversions may be necessary in 
watersheds with excessive runoff rates. Sometimes a 
number of small channels may be combined into one 
channel for greater economy of construction and sav- 
ings in right-of-way. Cast-in-place concrete, grouted 
stone riprap and sacked concrete have been success- 
fully used for bank protection. 

Where low-banked streams are actively eroding 
their banks, special protection is necessary. Some- 
times this can be accomplished through the use of 
concrete “‘jacks.’’ When placed along the eroding 
bank, they tend to slow the water, causing deposition 
of sediment and debris. Because of their unusual 
shape, such structures do not easily wash out. In- 
stead, they tend to dig in further when subjected to 
the action of flowing water. Concrete jacks have been 
successfully used for bank protection on Wyoming’s 
Riverton Reclamation Project; similar units have 
been used along the Rio Grande in New Mexico. 


Sacked lean-mix concrete was used at critical locations to protect 
banks of Walnut Creek in California against erosion. 
Courtesy of Soil Conservation Service 


Precast concrete “jacks’ were used to stop erosion of banks of 
Five Mile Creek near Riverton, Wyo. 


13 


FLOOD CONTROL 


Flood control is different from watershed protec- 
tion in that it is designed to provide a different degree 
of protection. The watershed protection program is 
concerned with the control of small, regularly recur- 
ring floods in small watersheds. On the other hand, 
flood control programs include major structures on 
the main streams or primary tributaries of river 
basins. These are designed to reduce damage from 
infrequent catastrophic floods, particularly in the 
downstream area of the river basin. 


nll, x . 
Flooded residential section of Dallas, Texas, at the height of the 
1957 floods. United Press photograph 


The simplest and most obvious way to reduce 
damage from a major flood would be to move people 
and property out of the probable path of the flood. 
However, floodplain zoning or evacuation in most of 
our heavily settled river valleys would be both expen- 
sive and very difficult to establish and enforce. Since 
the floodplain is often the most desirable land for 
residential, industrial and agricultural use, its protec- 
tion is mandatory in most cases. 


14 


The two flood control methods in general and satis- 
factory use today are: (1) limiting the flow in streams 
by temporarily impounding excess water in reservoirs; 
and (2) controlling the size and location of stream 
channels. The latter may involve artificial deepening 
or widening of the channel, removing channel 
obstructions, and constructing levees or floodwalls. 

A reservoir exclusively for flood control is almost 
always empty, or nearly so, since the outlet is kept 
open to permit normal flows to pass. During a period 
of excessive runoff, when the uncontrolled stream 
would overflow its banks, the flood control reservoir 
temporarily stores all or a portion of the flow. The 
entire runoff flows into the reservoir, while the dis- 
charge gates prevent outflow from the reservoir in 
excess of stream channel capacity. The excess run- 
off stored in the reservoir is later released at a rate 
within the channel capacity. Such operation of the 
reservoir will effectively prevent flooding in those 
portions of the stream below the reservoir that do 
not receive water from other sources. 

Typical af the single-purpose flood control dams 
built by the Corps of Engineers is Bluestone Dam, 
near Hinton, W.Va. It is located on the New River 
and is an important part of the comprehensive plan 
for flood control for the Ohio and Mississippi rivers. 
It is a concrete gravity-type dam, 165 ft. high and 
2,048 ft. in total length. Its 1,490-ft. concrete spill- 
way provides for safe passage of floodwaters in excess 
of storage capacity, while normal low flows and after- 
flood releases are passed downstream through 16 
sluicing conduits. While it is now primarily a flood 

control structure, authority exists for installing hydro- 
electric power at some future date. 

Since it is usually more economical to increase the 
size of a dam to fulfill additional purposes—such as 
water supply, irrigation, power or navigation—than 
to build other dams for those purposes, a multiple- 
purpose dam will usually be lower in cost than several 
single-purpose dams. The portion of the cost allocated 
to flood control will thus be less than the cost of a 
single-purpose flood control dam. This, of course, ef- 
fectively reduces the cost of flood control and increases 
the benefit-cost ratio. Therefore, the trend has been 
toward more multiple-purpose dams. Most of the re- 
cently built major dams have been designed for flood 
control, irrigation, navigation and /or power, in com- 
bination. This multiplicity of purpose and benefits 
has justified such structures as Grand Coulee and 
Hoover dams, which are considered to be among the 
engineering wonders of the modern world. 

Another example of a large multiple-purpose struc- 
ture is Clark Hill Dam in Georgia and South Carolina, 
on the Savannah River. This dam was designed to 


reduce flood damage in the lower Savannah River 
Basin, to generate hydroelectric power and to stabilize 
streamflow for navigation. Subsidiary uses are recrea- 
tion and wildlife development. Overall length of the 


dam is 5,680 ft., while the concrete section is 2,282 
ft. long with a maximum height of 200 ft. Flood dis- 
charges pass over the 1,016-ft. long concrete spillway, 
the flow being controlled by 23 Tainter gates. 


Bluestone Dam near Hinton, W. Va., is a single-purpose flood control dam. Photograph shows concrete spillway and a portion of an abutment. 
Courtesy of Corps of Engineers 


er 3 5 Z 


Clark Hill Dam near Savannah, Ga., is a multiple-purpose dam. Courtesy of Corps of Engineers 


DAMS 


Dams to create flood control reservoirs are usually 
built of concrete, earth or rock, although some earlier 
dams still in use are of masonry or timber. Selection 
of type for a given location is usually based on eco- 
nomic considerations, which require a careful evalua- 
tion of the primary purpose of the dam, the condi- 
tions prevailing at the dam site, the hydraulic factors 
imposed by the hydrology and the stream’s hydraulic 
characteristics, and the climatic conditions. Condi- 
tions at the site that should be considered include 
character of the foundation, topography, availability 
and proximity of construction materials, and accessi- 
bility to the dam site. Any type, and practically any 
height, of concrete dam can be built on a solid rock 
foundation. Concrete dams may also be built on less 
solid foundations, such as granular riverbed material, 
if adequate measures are taken to prevent excessive 
seepage and to prevent excessive foundation stresses 
and movements. A narrow, symmetrical canyon site, 
with adequate foundation and abutment rock, will 
be favorable to the construction of a concrete arch 
dam. Long hauls to aggregate supply sites may make 
a buttress-type dam advisable. Spillway and diver- 


sion requirements will also help determine the type 
of dam to be constructed at a given site. For instance, 
large overflow spillways are readily adaptable to con- 
crete dams, while earth or rockfill dams require con- 
crete spillway sections or provision for some type of 
separate spillway. 


EARTH AND ROCKFILL DAMS 


Earth dams are favored where foundation mate- 
rials are pervious, for their wide bases create longer 
percolation paths and tend to minimize percolation 
losses. Earth dams are also favored when compressi- 
ble foundation materials are encountered and a high 
structure is contemplated, since the earth structure 
has somewhat greater flexibility. Where little or no 
seepage can be tolerated, a cutoff trench is excavated 
to an impervious stratum and backfilled with imper- 
vious soil. Concrete cutoff walls, usually located ap- 
proximately on the axis of the dam, have been used 
and are recommended if appreciable foundation or 
fill settlements are not expected. Cutoff curtains, 
created by grouting the foundation with portland 
cement, have been used with success where the 
foundation materials were sufficiently coarse to re- 
ceive the grout. Recently, considerable success has 
been achieved by constructing a cutoff by means of 
interlocking mixed-in-place concrete “‘piles.”’ 

Design of an earth dam must take into account the 
stability, compressibility and permeability of the 
foundation and the embankment itself under the 
various possible operation conditions. 

The rockfill dam is a specific type of earth dam and 
design methods for strength and stability are quite 


Left— Top of mixed-in-place concrete pile cutoff wall for the spillway section of Slaterville Diversion Dam of the Weber Basin Project in Utah, 


Right— Constructing concrete pile cutoff wall used for Slaterville Diversion Dam. This processis patented by Intrusion-Prepakt, Inc., Cleveland, Ohio. 


Courtesy of Bureau of Reclamation 


similar. Since embankments of rock or gravel are of- 
ten more stable than earthfills, their upstream and 
downstream slopes may be steeper. Hence a rockfill 
dam usually requires less material than an earthfill 
dam does. However, a rock or gravel embankment 
will require an impervious membrane at the upstream 
face or an inner impervious core to prevent percola- 
tion of water through the very pervious embankment. 

Both the upstream and downstream faces of an 
earth or rockfill dam may require protection against 
damage from wave action, rain and wind erosion, 
and burrowing animals. Natural stone riprap, where 
it is economically available, is most commonly used 
for protecting the upstream face. Downstream slopes 
are often protected with a layer of gravel or by sod- 
ding. The required thickness of upstream riprap will 
depend on the height of the dam, slope of the em- 
bankment, severity of wave action—a function of 
water depth, size of reservoir, and direction and 
velocity of prevailing and maximum winds—and size 
and quality of the rock. For dams 75 ft. or more in 
height, it is customary to require at least 3 ft. of 
riprap. In the case of earth dams the riprap should 
be laid on a 6- to 12-in. filter blanket of finer rock 
or gravel of such gradation as to prevent “piping”’ 
of the finer embankment material. 

Concrete-paved upstream slopes have been used 
on a number of large and small earth and rockfill 
dams. Among these are the several 300-ft. high dams 
in the current expansion program of the Pacific Gas 
and Electric Co. in California; McKay Dam, a 180-ft. 
high gravelfill dam in Oregon, built in 1927 by the 
Bureau of Reclamation; Lake Mathews Dam, which 


forms a reservoir of the Metropolitan Water District 
of Southern California, built in 1937; and Oliver Dam, 
a 50-ft. high earthfill dam in western Nebraska, com- 
pleted in 1912. 

The thickness of concrete upstream facings of earth 
or rockfill dams has varied from 6 to 24 in. or more, 
depending on the height of the dam. On earthfill dams 
the concrete must be placed on a properly graded 6- 
to 12-in. filter blanket of rock or gravel to prevent 
hydrostatic uplift in case of a rapid drawdown of the 
reservoir. Such a filter blanket is usually not required 
for rockfill dams. A number of ingenious devices have 


McKay Dam, Umatilla Project, Ore. This view of the concrete-paved 
upstream face of the dam shows steps placed near the top to 
break up wave action and prevent overtopping. 


Courtesy of Bureau of Reclamation 


Construction of the concrete upstream face of Bear River Dam in California. This reinforced concrete surface varied in thickness from 1 ft. 
at the top to a maximum of 2.5 ft. at the bottom. Joints were provided at about 60-ft. intervals. Courtesy of Pacific Gas and Electric Co. 


been used to mix, transport and place concrete on 
slopes of dams. The facing, in most cases, has been 
placed in strips 10 to 25 ft. wide. The concrete surface 
has been struck off with screeds pulled up the slope 
by means of a winch at the top. On some very long 
embankments, longitudinally operated slipforms have 
been used. Reinforcement is generally used with con- 
traction joints to form about 10- by 25-ft. slabs. 

Laboratory research and field installations have 
demonstrated the engineering feasibility and eco- 
nomic advantages of a heavy blanket of compacted 
soil-cement as an alternative to natural riprap (see 
Fig. 4). This type of facing should be given consid- 
eration particularly when adequate supplies of accept- 
able natural riprap are not available within a reason- 
able distance of the dam site.* 


*For information on this type of construction see Sozl- 
Cement for Paving Slopes and Lining Ditches, available on 
request to the Portland Cement Association only in the 
United States and Canada. 


Oe alee cost ; LY sia. eer 
Soil-cement slope facing on test section at Bonny Reservoir, Colo., 
after two years of service. Compacted soil-cement is being tested 
for use in place of costly riprap. 


30' ! Dumped fill 


—— Moist earth cover <5 


Original ground surface 


See detail 


CONCRETE DAMS 


As a construction material, concrete has the ad- 
vantage of easy placement and control, economy and 
relative abundance of raw materials, high compressive 
and shear strengths, durability and low permeability. 
Depending on topography and foundation conditions 
at a particular site, one or more of the following types 
of concrete dam would be suitable: 

1. Gravity—straight or curved. 
AopAren 

3. Slab and buttress. 

4. Multiple arch and buttress. 
do. Massive-head buttress. 


Loadings on Concrete Dams 


Following is a list of the principal forces that may 
act on concrete dams. The possibility of each force 
acting, and its probable magnitude, should be con- 
sidered in stability and stress analyses. 

1. Weight of the concrete. 

2. Vertical and horizontal water pressures (res- 

ervoir and tailwater). 

3. Earthquake forces on the dam and water. 
Horizontal forces due to earthquake action on 
dam and water. 

Temperature stresses. 

Pressures due to silt accumulation. 
Ice pressures. 

Wave action. 

Uplift pressures. 


Fe SES le 


Concrete Gravity Dams 


Dams in this category resist the forces imposed on 
them mainly by their weight. Some gravity dams are 
curved in plan, in which case a portion of the load is 


carried by arch action. Hoover Dam on the Colorado ~ 


River and Shasta Dam in California are typical of 
this type of design and construction. At this writing 
the highest and most massive straight gravity dam is 
Grand Coulee on the Columbia River in Washington. 


Completed 
S/C layers 


/#—______——+ embankment 
LF 


Fig. 4. Details of compacted soil-cement facing for Bonny Reservoir test section. 


7! Rolled impervious 


Grand Coulee Dam on the Columbia River in Washington stores water for irrigation, flood control and power generation. 


Courtesy of Bureau of Reclamation 


Design of a concrete gravity dam involves deter- 
mining the most economical cross-section, or profile, 
that will result in satisfactory foundation loadings 
and concrete stresses. The dam also must be stable 
against overturning and sliding on the foundation.* 


, 


*See “Gravity Dams,” Treatise on Dams, Chapter 9, 
U.S. Department of the Interior, Bureau of Reclamation, 
1955. Also, “Gravity Dams,” Engineering Manual for Civil 
Works, Part CX XII, U.S. Department of the Army, Corps 
of Engineers, 1952. 


Hoover Dam near Boulder City, Nev. This concrete gravity arch 
dam was completed in 1936. 


Concrete Arch Dams 


An arch dam is stable because a large portion of 
the water and other horizontal loads are transmitted 
into the canyon walls by direct thrust. Examples of 
this type are Buffalo Bill Dam near Cody, Wyo., 
built of rubble concrete shortly after the turn of the 
century; and Pelton Dam, near Madras, Ore., con- 
structed in 1958 of conventional concrete. 

An arch dam is suitable and economical in a rela- 
tively narrow, deep canyon where rock foundations 
capable of resisting the arch thrusts without undue 
deformation are available. Where such rock forma- 
tions are present, a concrete arch dam will usually 
be economical if the ratio of crest length to height 
does not exceed 5 to 1; for very high dams and very 
favorable site conditions this ratio may be some- 
what greater.* 

In. the past the design of arch or curved gravity 
dams required much more time than the design of 
straight gravity dams. Recent developments in the 
adaptation of electronic computers to such problems 
have made possible the more rapid solution of such 
problems. 


*See “Arch Dams,” Treatise on Dams, Chapter 10, U.S. 
Department of the Interior, Bureau of Reclamation, 1955. 
Also, ‘‘Arch Dams with Arches of Variable Thickness,”’ 
R/C, Modern Developments in Reinforced Concrete, No. 21, 
Portland Cement Association, 1948 (available on request 
only in the United States and Canada). 


19 


Buffalo Bill Dam near Cody, Wyo. This rubble concrete arch struc- 
ture, completed in 1910, stores water for irrigation and power 


generation. Courtesy of Bureau of Reclamation 


20 


Concrete Buttress Dams 


’ 


Buttress-type, or “‘hollow,’’ concrete dams are 
composed of two principal structural elements: (1) 
the upstream, water-supporting deck or face; and (2) 
the buttresses that support the deck. The advantage 
of buttress dams is twofold: smaller quantities of 
concrete are required than for gravity dams, and unit 
pressures on the foundation are usually lower.* 

The most common type of buttress dam is the slab 
and buttress, which consists of a sloping deck of flat 
slabs supported by buttresses. The flat-slab deck is 
usually designed as simply supported reinforced con- 
crete slabs. Stony Gorge Dam in California and 
Possum Kingdom Dam in Texas are excellent ex- 
amples of early and recent slab-and-buttress dams, 
respectively. 

The multiple-arch dam is similar to the slab-and- 
buttress dam except that the upstream face consists 
of a series of arch-barrel segments instead of flat 
slabs. Its advantage is that it can carry a greater 
load for a given span between buttresses than is eco- 
nomically feasible with flat-slab construction, or it 
can span a greater distance with a given load. 
Bartlett Dam, in Arizona, and Mountain Dell Dam, 
near Salt Lake City, Utah, are good examples of 
multiple-arch dams. 

Massive-head buttress dams are formed by flaring 
the upstream edges of the buttresses to span the dis- 
tance between the buttress walls. Since the enlarge- 
ment at the upstream face is either curved or diamond- 
shaped, the pressure of the water produces major 
principal compressive stresses and relatively small 
tensile stresses in the buttress. No massive-head dams ~ 
have been built in the United States or Canada, but 
several have been built in other countries. Las 
Virgenes Dam on the San Pedro River near 
Chihuahua, Mexico, is a good example of this type. 


Prestressed Concrete Dams 


While only a limited number of prestressed con- 
crete dams have been built, all of them in Europe, it 
appears that this type of design has some advantages 
and should be given more widespread consideration. 
Prestressing wires, cables or bars, anchored in the 
foundation rock below the dam and extending verti- 
cally to its crest, make possible the elimination of a 
portion of the mass concrete required for stability of 
the usual type of concrete dam. 

Allt-na-Lairige Dam in Scotland, constructed in 
1953-56, is an example of this type of construction. 

*See “Buttress Dams,” Treatise on Dams, Chapter 11, 


U.S. Department of the Interior, Bureau of Reclamation, 
1950. 


Mountain Dell Dam near Salt Lake City, Utah, a multiple-arch structure, was constructed in 1915 and raised 40 ft. in 1925. It forms a 
3,200-acre-ft. water supply reservoir for Salt Lake City. 


Spillway and outlet conduit for Bartlett Dam, a concrete multiple-arch structure on the Salt River Project, Ariz. This dam is used for flood 
control and irrigation. Courtesy of Bureau of Reclamation 


It is 1,360 ft. long and has a maximum height of 73 
ft. above rock surface. Its design was based on the 
prestressing principle first used for raising and 
strengthening Cheurfas Dam in Algeria in 1934, and 
subsequently applied to other dams. 

Estimates based on the gravity and prestressed 
designs for the Allt-na-Lairige site indicated a cost 
saving of about 15 per cent for the prestressed design. 
In this case, however, it was decided to take advan- 
tage of the lower-cost prestressed design by building 
a higher dam than originally planned. The design 
adopted provided reservoir storage about 14 greater 
than would have been provided by a gravity dam of 
equal cost. 

As mentioned earlier, prestressing has been used 
to raise existing dams safely and economically. The 
height of prestressed dams, such as the Allt-na-Lairige 
Dam, also may be increased at a future date simply 
and economically. 


SPILLWAYS 


Spillways are designed to release surplus water 
from the reservoir in order to prevent overtopping 
and possible failure of the dam. The safety of the 
dam and downstream developments is dependent on 
proper functioning of the spillway under the most 
adverse conditions. Therefore, design of the spillway 
is one of the most important parts of dam design. 
It requires hydrologic studies to estimate the volume 
of water to be handled, hydraulic design to deter- 
mine the necessary dimensions, and structural design 
to ensure stability.* Several types of spillways, with 
their particular characteristics, are: 

1. Overflow spillway. This is one in which the water 
flows over a concrete dam, or the concrete spill- 
way portion of an earth dam. (See photograph 
below.) 


Concrete overflow spillway for Hoover Dam on Big Walnut Creek 
in Ohio. This earthfill dam forms a 60,200-acre-ft. water supply 
reservoir for the city of Columbus, Ohio 
e s " : mn ud * cae : as 


Fig. 5. Plan and section of a typical chute spillway. 


2. Chute spillway. This is an open channel structure 
for passing water around the dam into the river 
channel downstream from the dam. Chute spill- 
ways frequently are located in an abutment at 
one end of the dam or in a saddle elsewhere in 
the reservoir. This type of spillway is most com- 
monly used in connection with earth dams, but 
has also been used to pass water around concrete 
arch and buttress dams (see Fig. 5). 

A minor variation of the chute spillway is the 
side-channel spillway, usually located in an 


*See “Spillways,” Treatise on Dams, Chapter 12, U.S. 
Department of the Interior, Bureau of Reclamation, 1950. 
Also, “Spillways,” Engineering Manual for Civil Works, 
Part CX XIV, Chapter 2, U.S. Department of the Army, 
Corps of Engineers, 1956. 


Chute spillway for St. Mary’s Dam, Alberta, Canada. 


Courtesy of Department of Agriculture, 
Prairie Farm Rehabilitation Administration, Canada 


Side-channel spillway at Municipal Water Authority's impounding 
dam in Williamsport, Pa. 


abutment very close to the dam itself. The water 
flows into the spillway over a concrete ogee weir 
section roughly parallel to the spillway chute. 

3. Tunnel spillway. This consists of a tunnel 
through an abutment of the dam. Flow into the 
tunnel is controlled in the same manner as flow 
into a chute spillway. This type of spillway is 
often used when diversion of the stream during 
construction of the dam is through a tunnel. A 
portion of the diversion tunnel is then used as 
the permanent spillway tunnel. 

A type of tunnel spillway in which the water 
spills over a circular weir and down a vertical 
or inclined shaft into the tunnel is known as a 
morning-glory spillway. A good example is the 
spillway at Owyhee Dam (see photograph above 
right). 


OUTLET WORKS 


Outlet works are designed to pass normal stream- 
flows or to release water from the reservoir as re- 
quired by its operation plan. In some cases, portions 
of the permanent outlet works are used for stream 
diversion during construction of the dam. Ungated 
Outlets have been used on some flood control reser- 
Voirs, particularly small ones, where regulation of dis- 
charges by the reservoir head is adequate. Important 
flood control reservoirs and practically all multipur- 
pose dams are equipped with gate-controlled outlets. 

Outlet works for concrete gravity dams, and for 
earth dams with mass concrete overflow spillways, 
usually consist of sluiceways through the concrete. 
Tunnels or cut-and-cover conduits also serve ade- 


Morning-glory spillway at Owyhee Dam in Oregon. 


Courtesy of Bureau of Reclamation 


quately as outlets. Final choice of type to be used 
depends largely on site conditions and economics. 
Where conduits pass through or under an earth dam, 
care should be exercised in their design and construc- 
tion to guard against leakage, which would be dam- 
aging to the earth embankment.* 


*See “Outlet Works,” Treatise on Dams, Chapter 13, 
U.S. Department of the Interior, Bureau of Reclamation, 
1950. Also, ‘Outlet Works,” Engineering Manual for Civil 
Works, Part CX XIV, Chapter 3, U.S. Department of the 
Army, Corps of Engineers, 1956. 


Rio Hondo outlet structure at Whittier Narrows Dam near Los 
Angeles, Calif. Courtesy of Corps of Engineers 


23 


CHANNEL IMPROVEMENTS 


Reservoirs alone seldom provide adequate flood 
control for a river basin. This is because of the many 
factors that contribute to flooding and the uncon- 
trolled flows from areas tributary to the channel 
below such reservoirs. Therefore, channel improve- 
ments—such as stream straightening and deepening, 
cutoffs, debris removal, levees and floodwalls—are 
necessary. Floodways further extend the benefit of 
channel improvements by allowing predetermined 
areas to act as ‘“‘safety-valve”’ reservoirs or channels. 
All of these flood control measures are used in the 
master flood control plan for the lower Mississippi 
Valley and in the Los Angeles County, Calif., Drain- 
age Area, examples of large and small river basins, 
respectively, for which flood control plans have been 
made. 


24 


sah f oe a er A 


ks, 8x12x18 in. 


om scour by 400,000 solid concrete bloc 


CHANNEL CHANGES AND CUTOFFS 


Channel changes and cutoffs are designed to shorten 
the course of rivers and increase their slope and dis- 
charge capacities. A great deal of this type of work 
has been done on the lower Mississippi River. By 
this technique the river distance between Memphis, 
Tenn., and Baton Rouge, La., has been shortened 
by some 170 miles. The effectiveness of these cutoffs 
was demonstrated in 1937, when, with flows greater 
that in the 1927 flood, the flood crests at Greenville, 
Miss., and Arkansas City, Ark., were from 8 to 14 ft. 
lower than in 1927. These cutoffs have also benefited 
navigation and reduced the cost of maintaining the 
channel section. Revetment, or protection of the 
banks, may be required for cutoffs, as well as for 
natural channels. 


LEVEES 


The levee, the oldest and one of the simplest flood 
control structures, consists of broad, low, artificial 
banks of earth built higher than the natural stream 
banks to confine the flow of the stream. Some 3,500 
miles of levees have already been built on the lower 
Mississippi River and its tributaries. Levees have 
also been built to protect the shores of inland lakes 
against wave action. 

Where stream banks or levees are subject to scour, 
as is the case at bends in a river or when velocities 
are high, some form of revetment or bank protec- 
tion is necessary. Many materials—including stone 


Dy ‘ Fe nee Gates NPE SIMI 


Bank of Lake Okeechobee, Fla., is protected against erosion by 
soil-cement paving, placed in 1949. 


Pit-run concrete upper-bank pavement above Huey Long Bridge 
near New Orleans, La. This pavement, 12 in. thick, has been in 
satisfactory service for over 40 years with little or no maintenance. 


riprap, soil-cement, precast concrete in various forms, 
and concrete paving—have been used successfully as 
bank protection for levees and natural channels 
wherever it has been possible to carry on such con- 
struction. The placement of cast-in-place concrete 
paving on the upper-bank levees of the lower Mis- 
sissippi River is an example of such revetment. * 
There are some similarities in the design of bank 
protection for levees, channels, and slope protection 
for earth dams. The requirements are somewhat dif- 
ferent, however, since a dam is usually subjected to 
more severe direct wave action than a levee, while 
a levee is frequently exposed to high velocities paral- 
lel to it. For small channels or where velocities are 
quite low, unreinforced concrete or soil-cement has 
been successfully used as bank protection. Many miles 
of unreinforced pit-run concrete upper-bank paving 
on the lower Mississippi River, still serving satis- 
factorily after more than 45 years, prove the service- 
ability of this type of revetment under mild to 
moderate conditions. Where velocities above about 8 
ft. per second may be expected or where failure of 
even a small portion of the revetment would be dis- 
astrous, reinforced concrete should be used. In either 
case some system of under-drainage may be needed 
to prevent failure of the revetment from hydrostatic 
uplift. 
~ *See Rudolf Hertzberg, ‘“‘Wave Wash Control on Missis- 


sippi River Levees,” Transactions of the American Society 
of Civil Engineers, Vol. 119, 1954, pages 628-638. 


25 


ee ls we 
Articulated concrete mattresses in place on bank of Miss 
Courtesy of Corps of Engineers 


The more difficult task of underwater stabilization 
has been successfully accomplished on a large scale 
by the use of articulated mattresses composed of pre- 
cast concrete sections, joined with metal clips and 
steel cables. Such mattresses have a long record of 
satisfactory service on the lower Mississippi River.* 
A gravel blanket to serve as a filter layer under the 
mattress may be necessary to prevent the water from 
leaching out the finer bank materials. Paving of the 
riverbank or levee above the shore end of the mattress 
completes the improvement. 


*See Raymond H. Haas and Harvill E. Weller, ““Bank 
Stabilization by Revetments and Dikes,” Transactions of 
the American Society of Civil Engineers, Vol. 118, 1953, 
pages 849-870. 


Top bank 
: Upper bank paving £ 
aK 5 
an 2 
Inshore edge of mat eS as ee ee eel 
anchored to steel Pa a we rs is as a re 
plate anchors 
Underwater 
mattress 


Fig. 6. Cross-section of revetment operation. 


26 


Mattress units, 4 by 25 ft. in size and usually 3 in. in- 
thickness, are cast on shore at centrally located sites 
(see Fig. 6). The finished units are transported on 
barges to the installation area. There they are transfer- 
red to the mat boat, fastened together on the launching 
ways to form a mattress and dropped overside into 
place. The shore end is anchored to deadmen in the 
bank. In this manner a continuous mattress is laid 
from above the normal high-water level to a point 
far enough out into the stream to prevent undermin- 
ing, which may be as much as 600 or 700 ft. When — 
the required length of mattress has been laid, the 
entire plant is moved upstream to lay a new section 
of mattress slightly overlapping the first. The upper 
bank is then paved, with the paving overlapping the 
mattresses (see Fig. 7). 


Mat boat 


Supply boat 
Mooring barge 


Edge of previous mat 


wa 


Clip or corrosion-resistant Each unit 3-i0L x 24'-11"(20 blocks) 
twist wire 


Steel launching cable Corrosion-resistant wires 


Fig. 7. Plan and section of 4- by 25-ft. concrete mattress. 


Concrete mattress is being launched. Control barge is to the left and mattress assembly is on the mat boat to the right. 
Courtesy of Corps of Engineers 


FLOODWALLS 


The floodwall is a special form of levee, used in 
locations, such as industrial, residential or transpor- 
tation centers, where levees are not economically feasi- 
ble. A floodwall is essentially a watertight concrete 
retaining wall of gravity, cantilever, buttress or 
counterfort design, which extends some distance 
above the ground to protect low-lying land behind 
the wall from flooding (see Fig. 8). Sheetpile or cel- 
lular construction is also suitable under some condi- 
tions. A particular case of the floodwall is the retain- 
ing wall, sometimes used to provide sidewalls for 
depressed flood channels.* 


*See ‘“‘Floodwalls,’’ Part CX XV, Chapter 1, and “‘Re- 
taining Walls,” Part CX XV, Chapter 2, Engineering Man- 
ual for Civil Works, U.S. Department of the Army, Corps 
of Engineers, 1948. 


Concrete floodwall on the Ohio River at Parkersburg, W.Va. 


Courtesy of Corps of Engineers 


Max. high water (1913) 


Reinforcing steel 


Fig. 8. Cross-section of typical floodwall. 


28 


Height and loading conditions will influence selec- 
tion of design and type of floodwall. For very low 
walls, which are sometimes used to extend the effec- 
tive height of a levee, the gravity type is frequently 
the most economical. For medium height walls, from 
about 10 to 20 ft., the cantilever design will usually 
have a cost advantage over either gravity or buttress 
walls. For walls higher than about 20 ft. the buttress 
or counterfort design will usually be more economical 
than the cantilever. 

Floodwalls are designed to be stable against over- 
turning and sliding. The wall must be designed so 
that the pressure on the foundation does not exceed 
the safe bearing capacity of the soil, or if pilings are 
used, so that the maximum allowable load per pile 
is not exceeded. Sometimes a cutoff or curtain wall, 
usually of sheetpiling, is used below the wall to 
lengthen the seepage line or to reduce hydrostatic 
uplift. A sheetpile cutoff is not effective in resisting 
lateral forces; batter piles are used if the passive re- 
sistance of undisturbed earth or rock is not sufficient. 

When a floodwall retains earth for all or a portion 
of its height, the magnitude and the distribution of 
the loading against it are greatly influenced by the 
design of the drainage system immediately behind 
and under the wall. The possibility of future sur- 
charge loads, such as railroads, highways or buildings, 
should be considered in the selection of loading cases 
for design of the wall. A special and quite efficient 
type of retaining wall is the ‘‘L”’ wall, commonly used 
for completely lined and enclosed channels. The base 
of the “‘L”’ performs the double duty of paving the in- 
vert and serving as the structural base for the wall. 

Tujunga Wash channel (see photograph on page 8) 
is typical of high-velocity channels of this type con- 


Floodwalls and paved invert of Frankford Creek flood control 
project, Philadelphia, Pa. 


—Symmetrical 
| about ¢ 


Longitudinal construction joint 


Compacted fill 


Outlets spaced 
50'-O" o.c.+ 


Construction joint 
—- yes Oo! eae a ., mpl F a — 9 


SAS wh at 
SEMAN 


“ys aS B A VA vy TF Ty sas T ~ — 
XDA TY ACO A IC ee eae 
= wa COAG AAAI OLIVA Z eT TON 


SZ th Val aps rere ; = ie ME, 


Drain material 


Fig. 9. Typical “L” wall channel section. 


structed since 1930 in southern California. As indi- 
cated in Fig. 9, these channels consist of two canti- 
lever retaining walls, their bases forming the paved 
channel invert. Contractors have developed in- 
genious and economical equipment and procedures 
for constructing such channels. 

Since a basic requirement of a floodwall is water- 
tightness, all necessary expansion, contraction or 
construction joints should be tightly sealed. The joints 
may be made watertight with noncorrosive metal, 
rubber or plastic waterstops. Traffic openings through 
a floodwall may be equipped for sealing at times of 
high water by the inclusion of suitable grooves for 
stoplogs. A floodwall should be designed to be higher 
than the highest flood of record. Because of the pos- 
sibility of a still higher flood, provisions should be 
made for extending its height in time of emergency. 
This may be done by providing stirrups to support 
flashboards on the crest of the wall. 

A sheetpile wall is well suited for situations where 
a fairly deep cutoff is necessary but where little height 
is required above ground surface. Such a wall is al- 
ways provided with a suitable cap, usually of cast-in- 
place concrete. A cellular wall has the advantage of 
providing promenade space on its top and may also 
be made higher if necessary. 

Installation of levees or floodwalls requires careful 
planning to provide for drain and sewer discharge 
from the protected area. This is especially true for 
gravity sewers, which should be provided with flood- 
gates to shut off reverse flow during periods of high 
water, and pumping facilities to bypass the gates. 


Filter material 


GRADE STABILIZATION 


Grade stabilization, if required, should precede or 
accompany the construction of levees or floodwalls. 
The principles involved in the construction of grade 
stabilization structures for natural streams or flood 
control channels are similar to those cited in Chapter 
2, “Stabilization Structures,” page 9, for the con- 
trol of gullies. That is, successive check dams or 
stabilizers must overlap each other vertically; they 
must be constructed on adequate foundations so that 
undercutting will be prevented, they must be ex- 
tended far enough into the stream banks to prevent 
their being bypassed; and they must be equipped 
with concrete aprons downstream to prevent scour 


Channel stabilizer on Cherry Creek, Denver, Colo. 


29 


—— 


Fig. 10. Typical cross-section of channel stabilizer on Cherry Creek, 
Denver, Colo. 


due to water flow. These are essentially the require- 
ments for overflow dams; a stabilizer is merely a 
special form of dam (see Fig. 10). 

The ultimate in grade stabilization is to pave the 
channel bottom completely. While this may be done 
in connection with banks that are not revetted, it is 
most often done in connection with retaining walls or 
paved sloping banks. With concrete paving, velocities 
in excess of 50 ft. per second have occurred without 
damage to the channel. With high velocities, curves 
in such channels should be spiraled and superelevated. 
Adequate subsurface drainage must be provided. 
Slotted asbestos-cement pipe, laid in a trench and 
surrounded by coarse gravel, has been very effective 
and economical for under-channel drains. 

Contractors have shown much ingenuity in devis- 
ing, developing and using equipment for lining flood 
control channels rapidly and economically. Slipform 
pavers are generally used for placing concrete paving 
on both the side slopes and inverts of flood channels. 
These usually operate longitudinally on rails. The 


concrete pavement. Courtesy of Corps of Engineers 


30 


Left—Stony Creek at Johnstown, Pa., before banks were paved with concrete. Right—Stony Creek after banks had been stabilized with 


Ws a ew I DYE jue Aeaee§ 
Slotted asbestos-cement pipe used for drains under concrete chan- 
nel pavement. 


same rails frequently support a moving platform from | 
which workmen place the membrane sealing com- 
pound for curing the concrete. 

Important flood control channels of the size of — 
Stony Creek at Johnstown, Pa., or the Los Angeles — 
River in California (see Fig. 11) are almost always — 


channels have been constructed of concrete 3 to4in. 
thick. The required thickness is determined largely 
on the basis of experience and engineering judgment 
Some of the factors influencing thickness are loca- 
tion and importance of the channel, velocity, debris” 
load and foundation conditions. 4 

For small and very short channels it will seldom 
be economical for a contractor to provide elaborate — 
equipment such as that used on the Los Angeles 
River and the Rio Hondo. Several simple but efficient — 


Fig. 11. Typical cross-section of Los Angeles River channel pavement. 


Concrete pavement construction for Los Angeles River channel. 
Courtesy of Corps of Engineers 


items of equipment were devised and built by the 
contractor to prepare the foundation and place con- 
crete lining in the Bitterbush Flood Control Channel, 
Orange County, Calif. All but a very small amount 
of handwork was eliminated by use of this equipment. 
In areas where sufficient quantities of large rock 
are readily available, grouted cobblestone has proved 
to be satisfactory and economical for invert and slope 
paving. The stone blanket, usually 12 to 18 in. thick, 
is constructed of cobbles ranging in size from 5 to 
12 in. (see Fig. 12). In a typical operation the cob- 
bles are placed on the prepared subgrade with clam- 
shell buckets and spread into place with bulldozers. 
After they have been placed they are flushed with 
water to wash down the fines. They should be wetted 
immediately before the grouting operation. 


Reinforced concrete 
side slope 


Symmetrical 
about ¢ 


150'-O" 
219" Construction joints @ 20-O'ce. min. |3'-¢0", 4°0" 
min. min. 


(5 @\2"0.c.E/W 
Construction joint 


Invert of low-water channel 


This specially designed machine was used on Bitterbush Flood 
Control Channel, Orange County, Calif., for fine-grading side 
slopes. A roto-tiller, mounted on an A-frame powered by a tractor, 
traveled up and down the slope on pipe rails and trimmed the 
subgrade to proper grade. 


A shop-built screed was used to pave the side slopes on the 
Bitterbush Flood Control Channel, Orange County, Calif. The screed 
was hydraulically operated from a tractor. An “outrigger” braced 
against the opposite slope kept the machine in place. 


|[2~ ..—Compacted earth fill—~ 


Original ground 


Fig. 12. Typical cross-section of grouted cobblestone levee pavement. 


Grouted cobblestone used to protect channel banks upstream from 
Whittier Narrows Dam in California. 
Courtesy of Corps of Engineers 


It is usually best to do the grouting in two courses. 
The first course penetrates to the bottom of the stone 
blanket and fills at least half the voids; the second 
course is placed as soon as the first course has stiffened 
enough that it will not flow. The grout consists of 
sand, cement and water, but no coarse aggregate. 
The slump must be-at least 6 in. Cement content is 
usually about 71% sacks per cubic yard. 

Some flood control channels expected to carry flows 
only very occasionally have been lined with lean-mix 
pit-run concrete and plastic soil-cement. For example, 
a flood control channel in Riverside County, Calif., 
was constructed of pit-run concrete in 1951. Since 
this channel carries floodflows only very infrequently, 
the low-cost lining should serve satisfactorily for 
many years. 


32 


CLOSED CONDUITS 


It may be desirable to enclose a stream completely 
for land reclamation or for aesthetic reasons. Some- 
times the top of a closed conduit serves to support 
the roadway of a street or alley; this has frequently 
been the case in congested metropolitan areas. Suc 
conduits are usually designed as rectangular concr ete 
box culverts, sometimes with one or more interme 
diate walls. ; 


. 
CT) 


FLOODWAYS AND DIVERSIONS 


Floodways, through which floodwaters in excess of 
the levee capacity can be routed, are included in 
some flood control plans to bypass major metropolitan 
areas, or to provide protection for important agricul- 
tural and industrial areas at the expense of relatively 
small and unimportant areas of the floodplain. Flood- 
ways have been used successfully in the lower 
Mississippi Valley. 

About 50 miles south of Natchez, Miss., 600,000 
cu.ft. per second can be diverted through the Old 
River into the Atchafalaya River for direct passage 
to the Gulf of Mexico. Another 600,000 cu.ft. per 
second can be diverted into the Atchafalaya through 
the Morganza floodway, 20 miles farther downstream. 
To provide protection for New Orleans, the Mississippi 
River stage at the city is controlled by diverting flood- 
waters in excess of capacity of the city’s levees 
through the Bonnet Carre floodway to Lake 
Pontchartrain and the Gulf of Mexico. This control 
structure is a 7,000-ft. gated concrete weir with a 
capacity of 250,000 cu.ft. per second. It was success- 
fully used as planned in the floods of 1937, 1945 and 
1950, and was very effective in reducing downstream 
flood stages. Another major bypass in the lower 
Mississippi Basin is the Birds Point-New Madrid 
floodway south of Cairo, Ill. These projects help 
greatly to control this mighty stream. 


The Morganza Floodway controls diversion of floodwaters from Mississippi River into the Atchafalaya River. This structure, founded on precast 
concrete piles, is 3,906 ft. long and has a capacity of 600,000 cu.ft. per second. Courtesy of Corps of Engineers 


Bonnet Carre Floodway was built in 1935 about 25 miles above 
New Orleans, La., to protect that city. Close-up of Bonnet Carre Floodway, discharge side. 


33 


CONCRETE FOR WATER 
CONTROL STRUCTURES 


The concrete in water control structures is gener- 
ally subjected to severe exposures of repeated cycles of 
freezing and thawing, wetting and drying, the move- 
ment of water at high velocity, and, in some instances, 
wave action. Therefore, the exterior concrete must be 
of the highest quality to ensure strength, durability, 
workability and economy of maintenance. To attain 
this quality, the basic principles of concrete making 
must be followed.* These are (1) the use of sound, 
well-graded aggregates; (2) low water-cement ratio; 
(3) properly designed mix; (4) careful placement; and 
(5) adequate curing. 

To these requirements should be added air entrain- 
ment. Air-entrained concrete was developed originally 
to improve the resistance of concrete to surface scal- 
ing caused by application of salts to pavements for 
ice removal. It has served this purpose very well. In 
addition, air-entrained concrete has many other 
beneficial properties that are particularly desirable 
in concrete for hydraulic structures. These are (1) 
increased resistance to freezing and thawing and wet- 
ting and drying; (2) increased workability and cohe- 
Siveness; (3) reduced segregation and bleeding; (4) 
reduced permeability; and (5) increased resistance to 
sulfate attack. 


QUALITY CONCRETE MIXES 


For mass concrete used in large dams—gravity, 
arch or buttress—the maximum aggregate size for 
-unreinforced or lightly reinforced sections at least 
30 in. thick should be 6 in. or less. Mass concrete 
made with large-size aggregate contains a relatively 
small amount of mortar and therefore has certain 
special advantages over concrete made with smaller 


*See Design and Control of Concrete Mixes, available on 
request to the Portland Cement Association only in the 
United States and Canada. 


It Dam in New York. 
Power Authority of the State of New York 


aggregates: (1) lower cost, due to lower cement con- 
tent; (2) less temperature rise, due to lower mortar 
content; and (3) less drying shrinkage, due to lower 
cement and water content per unit volume. 
Concrete for the interior of dams is usually made 
with a somewhat higher water-cement ratio than ex- 
terior concrete exposed to freezing and thawing and 
other deteriorating influences. The interior concrete, 
therefore, will contain less cement, sometimes less 
than 3 sacks per cubic yard, while the cement content 
for exposed concrete, 2 to 12 ft. thick, is usually at 
least 4 sacks per cubic yard. The required cement 
contents are governed by minimum strength required 
for the interior concrete and by maximum allowable 
water-cement ratio for durability of the exterior. 


CONCRETE PLACEMENT 


Mass concrete for dams is usually placed in lifts 
from 5 to 71% ft. deep; each lift is made up of a series 
of 15- to 20-in. layers. Successive layers of a lift 
should be placed in such a way that there will be 
no cold joints between layers. Complete and thorough 
vibration is necessary to consolidate properly the 
large-aggregate, low-slump concrete used in dams. 


JOINTS 


To obtain long-lasting hydraulic structures, hori- 
zontal construction joints should be given careful at- 
tention to ensure that they are properly constructed. 
The durability of concrete at such joints is affected 
by (1) the quality of the concrete immediately below 
the joint; and (2) the care taken in preparation of the 
joint surface before fresh concrete is placed for the 
adjoining upper lift. A number of methods can be 
used that will produce a satisfactory joint. 

A good way to ensure good bond and watertight- 
ness is wet sandblasting and washing of the lower 
lift immediately before placement of fresh concrete 
for the upper lift. Sandblasting should be done before 
the side forms are erected and should be limited to 
removal of laitance only, since further cutting and 
roughening of the joint will not ensure a good joint. 
A prerequisite, of course, is that the concrete in the 
upper portion of the lower lift be placed at the lowest 
slump consistent with proper placement and consoli- 
dation. It is particularly important to avoid wet 
mixes that might segregate or bleed, which would 
result in a layer of laitance and thus make cleanup 
of the joint more difficult. The concrete should be 
left relatively even. Just before placement of fresh 
concrete, the joint should be thoroughly cleaned with 
an air-water jet and a layer of cement mortar spread 
evenly over the joint surface. 


35 


36 


Fort Gibson Dam in Oklahoma. Courtesy of Corps of Engineers 


CONCRETE FOR WATER CONTROL 


Because of its many advantages—strength, dura- 
bility, economy and adaptability—concrete is the 
preferred construction material for all phases of water 
control, including soil stabilization structures, chan- 
nel improvements, and dams. Where human lives and 
important metropolitan areas must be protected, con- 
crete structures can be relied on for safety and perma- 
nence. Concrete is economical because of its long life 
and low annual maintenance requirement. Quality 
concrete does not require special treatment to protect 
it against extremes of temperature and moisture. 
Adequate designs are essential and competent engi- 
neers should be employed to prepare them for every 
important water control structure. 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products 
and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses 
of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial 
support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all port- 
land cement used in these two countries. A current list of member companies will be furnished on request. 


The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of 
complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and 
approved by a qualified engineer or architect. 


published by 


Sewers and 
( ivilixation 


CeO PENG AL NY Cae CU EOMeBUIN RASS) SUOLG AYR AO:N 


SAVERS PORTA WN Ors AU ENMU Eg, COR GAG Ol Oj WA Lil Noo ns 


Copyright 1959 by Portland Cement Association 


4 
? 


2 LAS 


4 The history of waste disposal is as old 
S as community living—far older 
than “‘history”’ itself. 


ps 


(Oriental Institute, University of Chicago.) 


Beevers and ( ivilization 


Man has always established his permanent communities 


near a source of fresh water—without which he can live only \ Hele; is known as yet Bide che 


SAE . h d “Indus Cul 
a few days. He needs water for drinking and cooking, for Ka satten Mhenjo-Daro. 


washing and innumerable other purposes. ee 


Ultimately, every drop of this water becomes waste. Some 
___ of it becomes highly polluted and is always offensive, often 
— dangerous, sometimes deadly. Its disposal soon becomes a 
public problem, growing more acute as the community grows 
larger. 

Public sewers have been unearthed at Nippur, in ancient 
Sumeria, dating from 3700 B.C. Scarcely more recent are the 
ruins of Mohenjo Daro, in what is now Pakistan—where 
almost every house had a “‘modern” bathroom. Public sewers 
were also in use at Tell Asmar, near Bagdad, in 2600 B.C., 
and at Nineveh and Babylon centuries before the dawn of 
the Christian era. 


sewers and 4 RY, 
civilization a 


Mesopotamia—where Man spent his infancy. Imperial Rome had the sewage problems of a modern city. a’ 


@ Baghdad . 
=, Al 
P 


®\® Kish 


Sippur 
Babylon 


Persian 


Gulf 


Ww 
aa 
a But the master plumbers of antiquity were the Cretans; be 
ee SR ed 1500 B.C. their palace of Minos at Knossos had facilities com} 
able to those of a modern hotel. é 
Iwo thousand years after its Fa ; oa 
construction, this section of a Rome, of course, was the great political and commercial capité 
Arian Aue a ees cane Geer es a of the ancient world. But Rome was not all temples, arches and 
the Smithsonian Institution : wig 
in Washington, D.C. forums, any more than New York is all skyscrapers, hotels an 


theaters. Rome was a vast maze of narrow, winding streets li 
with multistory wooden apartment buildings. Its great sewer, 
called the Cloaca Maxima, was built about 180 B.C.—and ¢ 
tinued to serve the Romans down to the present century. 
Except for the Cretan, none of these disposal systems made an} 
distinction between sanitary sewers and storm sewers. In alt 
all cases—even into 19th Century Europe—no attempt was made 
to treat sewage; wastes were merely carried to the nearest body 
of water and dumped. As cities grew more numerous and more 
crowded, public calamity became inevitable. ay 
In the middle of the last century, for example, recurring 


5 sewers and 
civilization 

Ancient Crete was a land of beauty, luxury, and a high 

degree of sanitation. Its people understood hydraulics, 

as their many fountains proved. Sanitary facilities were 

excellent, even by modern standards. In fact, a Twentieth 

Century traveler was impressed, after a heavy rain, to 

find all the drains of a Cretan villa functioning perfectly 

—four thousand years after they were installed! 


demics of deadly Asiatic cholera struck the city of 
London. It became tragically obvious that the great 
metropolis should not continue to deposit its un- 
treated sewage in the Thames. 
Similarly, this public awareness was taking place 
in Continental Europe. Thus slowly, the era of 
modern sanitary sewage collection and treatment 
began. 
In North America this development took place 
slightly later than in Europe, for obvious reasons 
of relative population density. Americans and Tr 
Canadians were thus able to profit from the expe- 
rience of others, almost from the very beginning. 


Rive | - 


ini int NES tae 
| JIN GM MY 
| i Ne = eat 


sewers and | 


civilization 


6 


= \Seaeeee522 


i 


sewers in modern America 


People today realize the enormous import- 
ance of proper sanitation, and are proud of the 
way the job has been done in our cities and 
towns. But the fact is that many of our sewer 
systems are inadequate for today’s needs— 
and will rapidly become even more inadequate 
in the years to come. There are four intercon- 
nected reasons for this. 


1. Population has been increasing at a tre- 
mendous rate, and forecasts indicate continu- 
ing increases. This will naturally increase the 
load on all utilities, including sewer systems. 
The population of the United States was 118 
million in 1925, climbed to slightly less than 
132 million by 1940; the 1950 census showed 
more than 150 million, and by 1958 the figure 


U.S. CENSUS 
PROJECTION - 


iN 


SSS Sees 
See NAR 
705258500008 


y | 


1860 ’70 '80 '90 1900 '10 "20 '30 40 '50 60 '70 '80 90 
Data from U.S, Public Health Service, Publication 609, and U.S. r ensus. i 


[| YEAR 


te” 
wi 


é a ay " 
fed is ~ athe ee jay 
oe yt ey % a NAgd is mq le? 
i ss bee” Sail fos ey: 
ives trees SL eRe oe 


NUMBER OF COMMUNIT 
SERVED BY SEWERS 
1860 10 
1900 950 
1940 | 8,516 
1957 11,131 


was 175 million. It is now predicted that by 
1975 our population will be approximately 220 
million. 


2. Urbanization 1s characteristic of our time. 
The mass migration from farm to city has re- 
sulted in mushrooming metropolitan areas 
which pose new problems. Many areas which, 
in the past, were more or less adequately served 
by septic tanks, are now too thickly settled for 
that kind of sewage disposal. As such areas 
become urbanized, they develop an acute need 
for a modern sanitary sewer system. 


3. Water usage per person 1s increasing 
steadily. A modern American community now 
uses about 150 gal. per person per day. This 
fact reflects a high standard of living and a 
widespread prevalence of water-using appli- 
ances. But it adds to the burden of the sewer 
system. 


4. Industry is spreading out to former fringe 
and rural areas, along with new residential de- 
velopments. The trend is a great stimulus to 
the economy of a growing community. But 
many industries add heavily to the volume of 
domestic sewage. 

Efficient new sewers are needed now—more 
than ever before. Even present needs are not 
being fully met—and today’s sewers must be 
designed to satisfy the far greater requirements 
of the future. 


At Abusir, Egypt—a drain in 
the mortuary temple of the 


Pharaoh Sahure. 


(Oriental Institute, University of Chicago.) 


MH THER 


HAE 


il 


I 


ia 


a 
\_ | 


sewers and 
civilization 


sewers and 
civilization 


collecting lines 


The drawing shows, in highly simplified form, the 
various elements of a sanitary sewer system. 

The house connection collects sewage from an indi- 
vidual building. 

A lateral receives sewage from several house connec- 
tions. 

A submain receives the flow from two or more laterals. 

A main receives the flow of two or more submains. 

An intercepting sewer receives the flow of several mains. 

An outfall sewer receives flow from the collection sys- 
tem and conducts it to the point of final discharge or 
to a treatment plant. 

Gravity flow is used wherever the terrain permits; 
where it does not, sewage pumping stations may be in- 
stalled as needed. 


house connection 


TYPICAL SANITARY tae 


SEWER SYSTEM ae 


ELEMENTS 


2 


sewers and the growing community 


The advantages of a good sewer system are many, 
but the most important of them is the way it safeguards 
the health of the community. Sewers help to protect 
against typhoid fever, dysentery and other diseases 
caused by water-borne wastes. They prevent ground 
water contamination that may result from individual 
waste disposal. They also eliminate a prime breeding 
and feeding place for flles—especially where garbage is 
put directly into the sewer through the use of household 
grinder units. 

Economically, a good sewerage system benefits the 
community in many ways. Sewer costs are very moder- 
ate, especially when long service life and low mainte- 
nance are taken into consideration. For the individual 
resident, a house connection 1s actually less expensive 
than temporary sewage-disposal facilities—which have 
to be cleaned out or replaced periodically. Lateral and 
main sewers are paid for by the community over a 
period of years, depending on the bonding term. 

Sewers are an unseen but powerful force in commu- 
nity development. They raise the desirability and value 
of property. They attract forward-looking neighbors— 
residential, commercial and industrial. They make pos- 
sible the development and growth of a well equipped, 
self-sufficient community, a source of pride to its citizens. 


+t 


Two powerful ar 


sanitation ‘are the organisms that | 
hat | 
e) and typhoid 


cause cholera (abov 
(below) *. 


% 


‘& 


) 
| 


‘ he ah ft 
guments for good , \ 


sewers and 
civilization 


» *% 
. 


sewers and 
civilization 


10 


concrete for quality sewers 


The great strength and long service life of concrete 
have recommended its use 1n sewer construction since 
ancient times. Natural cement concrete was used in 
building Rome’s huge C/oaca Maxima, portions of which 
were in service for more than 2,000 years. Similar ma- 
terial was used in the large sewers constructed in Paris 
from 1833 on—some of which are still functioning. 

Concrete pipe came into use shortly after the Ameri- 
can Civil War, and many of the sewers constructed then 
are still in service. Their record over the decades has 
been one of meeting rigid standards of quality and, at 
the same time, intense economic competition. In present- 


Fiction’s Jean Valjean fled through 
a Parisian sewer like the one shown 
above. It is the prototype of the one 
shown at left, a modern big-city 
facility under construction in 
Chicago. 


day practice, portland cement concrete 
pipe sewers are proving their efficiency, 
durability and economy in widely varying 
locations and installations. They range in 
size from small 4-in. house connections to 
mammoth 12-ft. outfall sewers. 
Cast-in-place concrete sewers also have 


11 


a distinguished service record, as well as 
unique adaptability to unusual conditions 
and variations of terrain. 

Regardless of the type of construction, 
concrete is preferred in modern sewers 
because of the characteristics of the ma- 
terial itself. 


sewers and 
civilization 


sewers and | 12 
civilization 


| 


i 


concrete sewers for economy 


The use of concrete in sewer construction permits 
many economies that are unattainable with other ma- 
terials. 

Concrete sewer pipe 1s a mass-production, machine- 
made product which meets rigid specifications and con- 
forms to exact tolerances in sizes and dimensions. As a 
result, resistance to flow is very slight; smaller pipe can 
be used to carry a given volume. 

Breakage loss during transportation or installation is 
held to a minimum by the great internal strength of 
concrete. 

Long service life and low maintenance mean low 
annual cost—the true measure of economy in any con- 
struction material. 

Finally, besides the amount of municipal funds to be 
invested, it is also important to consider ow and where 
the money is to be spent. Concrete pipe for sewer con- 
struction can be manufactured with local labor, at or 
near the job site. The materials are usually obtained 
locally, or within a reasonable haul. Thus, more of the 
money spent on concrete sewers remains in the com- 
munity. 


Dotted lines indicate the drainage system in the 
valley and mortuary temples of Egypt’s Fifth 


Dynasty Pharaoh Sahure. 
(Oriental Institute, University of Chicago.) 


ae 


3 sewers and 
civilization 


concrete sewers for strength 


Reinforced concrete can be designed to meet any 

conditions of load or depth of backfill. The American 
Society for Testing Materials (ASTM) provides specifi- 
cations for several classes of concrete pipe to meet 
different conditions of load. 

Today’s concrete technology includes the use of proc- 
essed and graded aggregates, proper proportioning and 
~ control, adequate curing and modern equipment. Either 
concrete pipe or site-cast concrete can be made to attain 
any degree of quality and strength that may be required. 
—____ Inaddition, cast-in-place concrete can be designed and 
built to fit any desired shape of sewer section, to avoid 
__ obstructions or take advantage of special conditions. 


sewers and 
civilization 


ii 


14 


concrete sewers for watertightness 


To serve its basic purpose, a sewer should be water- 
tight. This means that sewage leakage or ground water 
infiltration should be held to a minimum. Excessive 
leakage of sewage to the surrounding ground could 
cause contamination of water supplies or lead to open 
ponds which could become odorous and dangerous 
nuisances. Leakage could also cause structural failure of 
the sewer by washing away bedding and backfill earth. . 
Infiltration is the passage of ground water into the ; 
sewer, which increases the liquid flow quantity. If such 
infiltration 1s possible, tree roots and silt may also enter 
the sewer. The adverse effects of these actions are varied. 
First of all, such roots and silt may clog the sewer and 
cause the sewage to “back up” into houses or to over- 
flow manholes. Secondly, if the sewer does not clog, the 
excessive flow may overload sewage collection and treat- 
ment facilities. 
Modern concrete pipe jointing materials and construc- 
tion methods make watertight joints easily attainable. 


Ground surface — eg 


15 


concrete sewers for durability 


The wearing qualities of concrete have been proved 
repeatedly by laboratory tests, and by its record of 
service over many decades. Concrete’s resistance to 
wetting, drying and temperature changes is universally 
recognized. And the smooth interior surface of concrete 
pipe resists abrasion from any granular material that 
may be carried in suspension. 

Since the first concrete pipe sewer was built in 1842, 
thousands of miles of concrete pipe sewers have been 
built in all parts of the United States. This nationwide 


Bea, RANA Pe sy record of successful use proves the durability of con- 
these appointments in 2300 B.C. crete pipe. 


(Oriental Institute, University of Chicago.) 


modern AMERICA NEEDS 
modern SEWERS 


sewers and 
civilization 


For further information about sewers and sewage 
treatment works, their functions, basic principles 
of design, construction and financing, 
the following materials are available . 
from the Portland Cement Association: A My oA) 


Literature: 
CONCRETE SEWERS 


CONCRETE SEWER PIPE FOR ECONOMY AND SERVICE ON, 
FINANCING WATER AND SEWAGE WORKS aye 


SEWAGE TREATMENT WORKS ! iy 
UNTREATED SEWAGE—A COMMUNITY MENACE ; my) 
SEWAGE TREATMENT PLANT DESIGN GUIDES Daya ues iy Nes 
ee Las Fay 19) y 
= rs he / 
Film: BI) 
SEWERS, A HIDDEN COMMUNITY BENEFIT Be). 
me) 
= 
te (Ag 


The activities of the Portland Cement Association, a national organization, are limited to scientific 
research, the development of new or improved products and methods, technical service, promotion and 
educational effort (including safety work), and are primarily designed to improve and extend the uses 
of portland cement and concrete. The manifold program of the Association and its varied services to 
cement users are made possible by the financial support of over 70 member companies in the United — 
States and Canada, engaged in the manufacture and sale of a very large proportion of all portland 
cement used in these two countries. A current list of member companies will be furnished on request. Nad 


Printed in Wiehe 


Portland Cement Association 


= + : 
See 


best 


Center cover photo courtesy U.S. Bureau of Reclamation. 


© Portland Cement Association 1960 


Concrete Pipe 
Irrigation Systems 


Portland Cement Association 33 West Grand Avenue Chicago 10, Illinois 


Contents 


Types of Pipe Irrigation Systems. .7.>. 7) 32 eae 3 
Economic Justification of System Used............ 5 
Hydraulic Design.:.......- 550-28 4. =e 6 
Pipeline Structures. .....<... 1.2.22...) 550 Bil 
Pipe Manufacture. ........)..:.2:..25))3 eee 15 
Construction 533.020). 3 Soe oe 16 
Concrete for Structures... .. ...:...+..:.2 ee 22 
Additional References. .................) =e 23 
Foreword 


The material in this booklet is the result of observa- 
tions and research on design and construction of modern 
irrigation systems by both private concerns and govern- 
mental agencies. The purpose of the booklet is to fur- 
nish up-to-date information to engineers responsible for 
the design of irrigation systems. 

The purpose of economic engineering design is to pro- 
duce an adequate facility at the lowest total annual 
cost. There must be proper balance between first cost, 
maintenance and service life. Only when all the factors 
have been included in the design study can a facility 
be considered properly engineered. 


Types of Pipe 
Irrigation Systems 


A typical irrigation system consists of mainlines and 
laterals, both of which may be open canals, pipelines, 
or a combination of these. Many distribution systems 
are built entirely of underground concrete or asbestos- 
cement pipe. The purpose of an irrigation distribution 
system is to convey water from a supply canal or reser- 
voir through the mainlines and laterals to individual 
farm delivery points located on these lines. Supplying 
the required quantity of water at the desired operating 
level is easily and economically done through a pipe 
distribution system. Different techniques for regulating 
these deliveries are required for the three principal types 
of pipe distribution systems. 


Open System 


In the past, most pipe irrigation systems have been 
“open,” or limited-pressure, systems. Vertical open-top 
stands equipped with overflow weirs or baffles are placed 
in the line to raise upstream line pressures to desired 
values. The open irrigation system is operated very 
much like an irrigation system that consists wholly of 
surface canals and ditches. In both cases the flow into 
the laterals and sublaterals and to the delivery points 
is controlled by simple slide gates. To avoid waste of 
water, it is necessary that the amount of water turned 
into the system be just equal to the sum of all the de- 
liveries from the system. If more than the desired 
amount of water is delivered to the system, the excess 
will be lost through a wasteway or by overflowing one 
or more of the baffle stands. 


Open systems generally are designed with maximum 
pressure heads of about 25 ft. This is to limit the height 
of structures as well as the internal pressure on the pipe. 
Therefore, the smaller lines of such systems may be built 
with low-cost unreinforced concrete irrigation pipe. Pipe 
used in such systems should meet the test and inspec- 
tion requirements of current ASTM Standard Specifi- 
cations for Concrete Irrigation Pipe (C118). Operating 
heads on unreinforced pipe should be much lower than 
the test pressure requirements of those specifications. 
Based on a safety factor of approximately 6 applied to 
those test pressures, the following maximum pressure 
heads (to center of pipe) are recommended: 


LOAN eee Zoli: 
jain SPADE 
het GHA a 
lisitee SS WANier 
ZAIN ee elt. 
we Taee, F  aeaoage. 


Where these heads would be exceeded, or where ex- 
ternal loadings or unfavorable soil conditions are pres- 
ent, unreinforced pipe with thicker walls or reinforced 
concrete pipe should be used. Asbestos-cement pipe also 
may be used within the pressure limitations prescribed 
by ASTM and federal specifications for the various 
classes available. 

To prevent or minimize surging or nonuniform flow 
in an open system, careful consideration should be given 
to the location of structures, air vents and gates. A 
surge may be amplified as the water passes over suc- 
cessive stand baffles. Such amplification of surges may 
be prevented by locating baffle stands at irregular inter- 
vals. A tendency to surging usually can be eliminated 


Fig. 1. Profile of typical open system showing operation of baffle stands. 


by the installation of airtight covers on the stands. In 
effect, these modify the natural periods of oscillation of 
the adjacent reaches of line. Best results are obtained 
when the covers are applied at locations which will cre- 
ate a system with periods of oscillation that increase in 
the downstream direction. The covers should be 
equipped with vents to relieve positive pressures: and 
with vacuum control devices to limit negative pressures 
inside the stands.* 


Full-Pressure System 


The full-pressure pipe irrigation system is similar in 
principle to a municipal water system. In both cases 
it is necessary merely to open a delivery valve to get 
a desired flow of water. Such systems usually are some- 
what more expensive to construct since they require 
high-head pipe. Several factors tend to offset the high 
initial cost of pipe for the full-pressure system as com- 
pared with the cost of the open system. Probably the 
most important factor is that the full-pressure system 
eliminates waste of water and the necessity for drainage 
at the ends of laterals. The size of pipe required for 
full-pressure systems is reduced by two circumstances: 
(1) Valves and other fittings result in less head loss than 
do control structures for open systems; and (2) the 
higher-class pipe used has better hydraulic character- 
istics than the pipe customarily used in open systems. 

In a full-pressure system all flow from the pipelines 
may be stopped by closing all the gates and valves. The 
entire system, therefore, must be designed for full in- 
ternal pressure head measured from the maximum water 
surface at the reservoir, canal or other source of supply, 
plus waterhammer unless positive controls against its 
occurrence can be provided. Deliveries must be designed 
to operate properly under both the maximum head pos- 
sible and the minimum head available at full capacity 
operation of the entire system. 

Topographic factors, which would affect the feasibil- 
ity and cost of land preparation for surface irrigation, 
may dictate the use of sprinklers. Sprinkler mainlines 
and laterals may be operated directly from underground 
concrete pressure lines that are properly designed for 
such use. 

Valves in high-pressure lines may be subject to cavi- 
tation if the head differential across them is more than 
about 35 ft. See page 15 for a further discussion of this 
problem and special treatment that may be required. 

Precast concrete pipe used in full-pressure irrigation 
systems usually will conform to one of the following spec- 
ifications of the American Society for Testing Materials: 
C361 Reinforced Concrete Low-Head Pressure Pipe 
C76 Reinforced Concrete Culvert, Storm Drain and 

Sewer Pipe 

Asbestos-cement irrigation pipe for full-pressure sys- 
tems may be specified for heads of 50 ft. and higher. 
Available pipe diameters range up to 16 in. for most 
localities. 

*See C. S. Hale, R. E. Glover, P. W. Terrell and W. P. 
Simmons, Jr., “Control of Surging in Concrete Pipe Dis- 


tribution Systems,’’ Journal of the American Concrete Insti- 
tute, Vol. 25, No. 7, March 1954, pages 273-584. 


Semiclosed System 


The “‘semiclosed”’ pipe irrigation system combines 
some of the most desirable qualities of the open and 
full-pressure systems. Inexpensive unreinforced pipe can 
be used because the internal pressures in the lines are 
limited by constant-head float valves. Operating charac- 
teristics of the semiclosed and full-pressure systems are 
quite similar. However, the semiclosed system seems to 
be most economical for lines where the flow and the 
heads to be regulated by the valves are small. As the 
semiclosed system is limited in quantity of flow by the 
maximum size of available constant-head valves, the 
area served by a lateral is limited. Therefore, the semi- 
closed system is most suitable where the terrain justifies 
short laterals from the main service canal or line. 

Most of the commercially available constant-head 
valves are of two types: single disc or double disc. (The 
latter is also called a ‘“‘balanced”’ valve.) Several other 
types of valves to accomplish control of head are being 
developed. Most of these valves are not designed to 
effect complete watertight closure but simply to control 
the static head in-the line downstream. If positive clo- 
sure of the line is desired, some other means— gate valves 
or slide gates, for example—must be employed. 


Fig. 2. Schematic drawing of float-valve stand for semi- 
closed system. Height of water in the stand regulates flow 
from pipeline segment upstream into the stand. 


Economic Justification 
of System Used 


Selection of the type of system will depend on an 
evaluation of both construction cost and annual expense 
for operation and maintenance. Lowest total annual cost 
over the expected useful life of the system will deter- 
mine the most economical choice. 


First Cost 


To make a proper comparison of costs, a preliminary 
layout should be made of the several types of irrigation 
systems that would be suitable. Prices for each type and 
class of pipe should be obtained from pipe manufac- 
turers in the area to be served. As a general rule, the 
open (or semiclosed) system using inexpensive nonrein- 
forced pipe will be the least expensive to construct. 


Operation and Maintenance 


Operation and maintenance costs should include all 
salaries, wages, office expense, power consumption, 
equipment depreciation, interest on the investment, and 
any other costs expected in the proper function of the 
delivery system. To indicate the dollar amounts in- 
volved in some of these items, two examples from Cali- 
fornia projects are detailed below. One is an irrigation 
district operating a full-pressure system in the San Joa- 
quin Valley; the other is an open-type system in another 
part of the state. Both summaries are for 1957. 


Full-Pressure System 


Design and construction cost........ $10,617,000.00 
(Constructed 1953-1955) 
Total acres for which service is available..... 56,594 
Prcomserved (1957) ce. sees: ke ce eee es 48,000 
Miles of pipeline operated 
Miles of main laterals, 12-in. to 72-in. dia... ..41 
Miles of sublaterals, 12-in. to 24-in. dia....... BB} 
MLCT MTTUL LOS meee Rule Sele cit aah ay Sah ole’ 174 
Miles of pipeline maintained 
Under maintenance and repair contract.......58 
epllcovered by guarantee. ..3 6... 6m Sena Se 116 
Mineratine heads. © 2.5. Psd ss seas DOTA tOeLoUl tt 
Water deliveries 
Acre-feet delivered to farmers........... 157,591 
Acre-feet for groundwater recharge.........1,919 
Bee CED LOSSES a yt Were ey ds Sead PE Oe 700 
Acre-feet maximum delivery in one month. 30,877 
Masamum delivery rate; cisi.4.0 6 J. se, 545 
Pumped deliveries, per cent.................. 43 


Parcels served 


PeesaetliaeOnacres imen 2s oe Soe aha nk Cee, 95 
AAEM JIACECS Mo ee acl eh: CO ek tere Gl 67 
SUC mm aMa ere Wut ee oo ys Me Ae Ee es 133 
BS ImLOREZOLACTES aria Su ice Oo Ma ei Shan el: 50 
Pete LO OsACl eS tte hon fa 8 ee A a 25 
OU SACTCs Me ene Miran a 6 re, EA Ret ie LO 4 Syl 

OLAEMDILT CCL Si mene re on te SO ES ORE 501 


Labor 

hesidentiengimeer sere res. sink) teenie 46 oh ce as if 
CPA COxCLET Kk tigen aie eat Wt Rasa rca Bee om ahah a et 1 
Water: masters gy ae wena es ton rants eo cnx at gy 1 
Naintenance- LOreman wees aoe ee ee ees 1 
Hquipmentimecnianicn 04 ote ey ee ee 1 
Ditech: tenders sammy wre ore eee ee ind asic an i: 6 

LL OLG ISIC DOT teehee ethene Bont. he ae ae ita 


Cash disbursements (excluding water 
purchases and refunds) 


Administrative expenses (salaries, fees, 
Current expenses)". ie eee) ye eee $22,780.62 


Operating expense 
Salavies"andwages.-.. 408...) 06 sen $ 40,056.70 


Hléetrict powers ean wees eee 83,432.31 
Repairs and maintenance............ 8,788.49 
Fuelrand lubricants eos. oe SO (Liat 
General operating supplies........... 3,541.40 


Wibewel anbays) lew, . ce wicccocdoosecuds see aves 


Payroll itaxce te mei: 12 ee eo eee 812.70 

Telephone and telegraph............ 1,130.44 

Insurance and miscellaneous 

EX PETISES somite bOnets aenetitcan cht ey ERs 2,489.21 
Total operating expenses........... $143,329.97 


Capital outlay 
Prpelinesfaclitics sama sere tere oo $ 5,897.21 


Operating equipment............... 1,075.59 
Automotive equipment.............. 3,264.66 
Biildings See pecan ig ios teense 1,209.16 
Office equipimenta en tn ma uate ren, 884.00 

LOCI ECO DLCCLBOUUO) see tae eee $ 12,330.62 


Other disbursements 
Pension trust fund payments 
(including employes’ share).......... Gh TLD SS Shea 
Employes’ payroll taxes and insurance 


(including employes’ share).......... 6,779.43 
Assessment overpayment refunded.... 84.97 
$ 17,862.91 
Total operating and 
TROLTILLCM ONCE, COSL at a ee $196,304.12 
Electric power for pumping.......... — 83,432.31 
Total operating and maintenance 
COSLMEXCLULG LL SaDOLUET a wn eee $112,871.81 
Open System 
Design and construction cost........ $13,500,000.00 
(Constructed 1947-1954) 
Total acres for which service is available..... 72,662 
ACES IGELVEC HLOO.) eawe hase k sone oeha 0 ce auin acute 47,465 
Miles of pipeline operated.................... 475 
Miles of pipeline maintained by 
GISTTICUSPEISONNGL Awe as Mee area 2.4 aid cave Pe os 475 
Operating heads..........Generally less than 20 ft. 


Water deliveries 


Acre-feet delivered to farmers............ 282,350 
Acre-feet of maximum delivery in 
one:month 3%. 335.00 .6h ee eee ee 34,809 


Acre-feet of maximum delivery in one day. . 1,480 


Parcels served 


Nearly all deliveries made to 40-acre parcels 


Labor 
Water delivery 
Watermaster:\, 522: 5 2 Se eee 1 
Watermaster assistant... -- une ee 1 
Water: clerks 0a eee 3 
Chief hydrosrapher 2 eee ee ee iL 
Hydrographersis.. S455 (ae eee 3 
Zanjeros:.+ a2 OO ee eee 12% 
Distribution system maintenance 
General foreman (4% of 1 man’s time)....... Wy 
Pipe repalr’ Crew 54 ee eee ee 2 
Meter. servicemen '.5 29. 20 a ee ee 2 
Sereen cleanertay) 30 ee ee eee 1 
Total. labor: force ee 26% 


Cash disbursements 


Maintenance of distribution system 


Supervision. .c. Gagne aoe $ 6,318.46 
Salaries and wages--..>-5.- 555-45 - 30,916.70 
Vacation ae... its ee ee 4,639.25 
Sick leave cas sises tee ee 1,115.29 
Payroll taxes and insurance.......... 1,720.45 
Materials‘and supplies). 10,969.97 
Outside repairs and maintenance. .... 430.15 
Utilities; 3 Sco aan eee seme ae 26,457.68 
Equipment; Useqn 4 ee eae 20,036.75 
Telephone and telegraph............ 732.00 
Total maintenance expense......... $103,336.70 

Water delivery 
SUDELVISION enc. 4 ae ee ee $ 7,706.48 
Salaries oF ae hea ae nee ee 70,447.16 
VaCatloniaok 6. eee a eee 20,291.00 
Sick leaves sc. escrec eee eee 265.00 
Payroll taxes and insurance.......... 3,133.98 
Materials-and supplies;: 4.5 ee 791.38 
Outside repairs and maintenance..... LSOeLe 
Equipment use. a.0 0) ee eee 36,056.43 
Insurance and bonds................ 80.00 
Praveliog vectors eee ee eee 4.10 
Total water delivery expense........$141,965.54 
Prorata shop and storeroom expense... .$ 14,027.33 

Prorata general administrative 

and overhead expense................. $110,718.74 

Capital outlay 
Lateralextension=. «= (4024 ee $ 3,941.91 
Total 2u3n5 cooky. ee eee $373,990.22 


To assist in the evaluation of the operation and main- 
tenance costs in the preceding examples, the following 
summary is presented: 


Full-pressure Open 


system system 
Acres!Servedijiun., cet eee 48,000 47,465 
Separate parcels served..... 501 1,180 
Average size of parcel 
served. acres. = esr eee 96 40 
Acre-feet of water delivered... 157,591 282,350 
Average delivery per 
parcel, acre-feet............ 324 240 
Average delivery per 
acre, acre-feet............. 3.28 5.95 
Miles of pipeline operated. . . 174 475 
Miles of pipeline maintained. 58 475 


Average cost of operation and maintenance 
Full-pressure Open 


system system 
Including Excluding 
power power 
Per acre served....... $ 4.09 $ Zone 8.17 
Per acre-foot delivered . 126 0.72 sf 
Per parcel served...... 3,926.00 2,253.00 3,288.00 


Although these two districts are quite similar in size 
and location, they are significantly different in number 
and size of parcels and in water requirements. An engi- 
neer should carefully consider these and other factors, 
such as topography, climate, and types of crops, as he 
prepares an estimate of annual costs for comparison of 
several possible irrigation systems. 


Hydraulic Design 


Criteria 


The basis for design of any irrigation system is the 
quantity of water to be delivered at each individual 
turnout, the required pressure head at that point, and 
the rotation of deliveries to the several delivery points 
on the system. The rate of delivery and required pres- 
sure head depend on the area to be served, the type of 
soil, character of crop to be grown, and type of farm 
distribution system that will be used. The rotation— 
that is, the order, frequency and duration of individual 
deliveries—establishes the number of turnouts that can 
be served by one measuring device and the required 
capacity of the line. 

Most of the following information on design of pipe 
irrigation systems applies to any of the systems de- 
scribed previously, unless it is specifically or obviously 
limited to only one or the other. 

Required capacities of irrigation pipelines will depend 
on the number and rotation of deliveries and the capaci- 
ties of the various farm turnouts. The procedure for 
combining turnout requirements to determine line ca- 
pacities is basically the same in all systems, but numeri- 
cal values of the several factors may differ widely in 
various localities. The following set of rules will serve 


to illustrate the procedure and will help an engineer 
formulate rules for his specific project. Note that these 
rules are for one particular system only. They must not 
be used at any other location unless careful study and 
analysis show that they are applicable. 


Rule Area served, Pipeline capacity, 
acres cfs 
Lie 0 to 120 3 
43 120 to 240 6 
a 240 to 1,000 A/50 + 3 
4. 1,000 to 1,150 23 
5; over 1,150 A/50 


Rule 2 should be modified to provide A/50 + 3 cfs 
for 120 to 240 acres when the line serves more than two 
nonrotational deliveries or more than two sets of rota- 
tional deliveries. 

If the area served from a single supply line exceeds 
about 3,000 acres, a further reduction in pipe capacity, 
as determined by Rule 5, frequently is allowed because 
of the diversification of crops in the larger area. This 
reduction will depend largely on the engineer’s evalua- 
tion of the factors affecting the water requirement. The 
theoretical requirement as computed by Rule 5 seldom 
would be decreased by more than 25 to 30 per cent, 
and to this extent only when the area served is 100,000 
acres or more. 

Fig. 3 illustrates the application of these rules to por- 
tions of a pipe distribution system. 

It is assumed that each delivery, indicated in Fig. 3 
by a short diagonal line, has a capacity of 3 cfs and, 
therefore, each segment of the system must have a ca- 
pacity of at least 3 cfs. 

Segment (3)— (2) has a capacity of 3 cfs, since it sup- 
plies only 3 deliveries that are rotational. 


Fig. 3. Schematic plan of hypothetical pipe irrigation system. 


(1) A=20 (2) A=90 


20A 


/ 
Nez. 
Rotational deliveries —~ _ 


40A 40A 


A = Acres served 
Q= Flow,cfs (8) 
“= Delivery 


(3) 


Nonrotational deliveries4 


Segment (4)—(3) has a capacity of 6.4 cfs, as com- 
puted by Rule 2 modified. 

Segment (5)— (4) has a capacity of 8 cfs, as computed 
by Rule 3. 

Segment (7)—(6) has a capacity of 22.4 cfs, as com- 
puted by Rule 3. 

Segment (8)—(7) has a capacity of 23.0 cfs, as com- 
puted by Rule 4. 

In establishing the criteria and planning an irrigation 
system, consideration should be given to the possibility 
of future changes in the ownership of and farming plans 
for the area. If division of existing farms into a larger 
number of smaller units appears probable, this should 
be considered in planning and designing the irrigation 
system. 

For efficient and convenient irrigation on the farm, 
the water surface at the point of delivery should be high 
enough to provide a minimum head of 2 ft. above the 
ground surface at any point along the high side of the 
farm. The head loss in the farm pipeline or ditch, which 
must be considered in computing the necessary delivery 
elevation to meet this requirement, will depend on the 
rate of water delivery and the type of pipe or ditch lin- 
ing used. Delivery point elevations, as established by 
these criteria, should be satisfactory where a pipe farm 
irrigation system is used, but probably are higher than 
necessary for a surface ditch system. Delivery eleva- 
vations should be carefully considered and should be 
lowered if they would severely penalize the remainder 
of the distribution system. If this is not feasible, pump- 
ing should be considered as an alternate solution. 


Flow in Pipelines 


The hydraulic requirements of the line are computed 
by taking into account required delivery elevations, ac- 


A=\70 (4) A=250 (5) 
a 
XN 
N 
\ 
7 
40A oa 
a 
oo / 
woe 
pain 
he 
/ 
ji 


A=!050 (7) 


A=970 (6) VY 


cumulated demand flow, pipe friction and other losses. 
Computations are started at the delivery point farthest 
downstream. The maximum required pressure gradients 
and flow capacities of the various lateral lines are con- 
trols for the main lateral, canal, or pumping plant serv- 
ing them. Pipe sizes and gradients must be such that 
the required quantity of water will be available at the 
required head. 


Pipe and Structure Losses 


Tests of head losses in concrete pipelines have been 
made by a number of investigators. Friction loss coeffi- 
cients, to be used in standard formulas for the flow of 
water in pipes, have been developed on the basis of 
these tests and observations. 

Flow formulas* developed by Fred C. Scobey, and 
coefficients of friction recommended by him, are widely 
used for the hydraulic design of irrigation pipelines. 

V =C,H”*d°-5, and 
Q =0.00546C,Af°*d?-?5, in which 
d =inside diameter of the pipe, in inches; 

H =loss of head due to friction, in feet, per 1,000 ft. 

of pipe; 

C, =coefficient of friction for the type and size of pipe 

and method of jointing; 


See HW. Kine. Handbook of Hydraviies (clhird de 
tion), page 178. 


Fig. 4. Flow of water in concrete pipelines by Scobey’s formula: Cs 


100 


V =velocity of water in the pipe, in feet per second; 

Q =flow, in cubic feet per second. 

Recommended values of C, for several classes of pipe 

are as follows: 

C, =0.310—for dry-mix (tamped or packerhead) con- 
crete pipe not more than 21 in. in diam- 
eter and in pipe units not more than 3 ft. 
long, in which mortar joints are not fin- 
ished by hand on the inside of the pipe. 

C, =0.345—for wet-mix pipe not more than 21 in. in 
diameter and in pipe units not more than 
3 ft. long; and for dry-mix pipe in pipe 
units at least 4 ft. long, with carefully 
smoothed interior mortar joints or rub- 
ber-gasket joints without interior mortar 
finishing. 

C, =0.370—for pipe at least 24 in. in diameter and 
in pipe units at least 8 ft. long. The units 
should be sufficiently uniform in size and 
shape that there will be only minor off- 
sets in the interior surfaces when the 
pipeline is finished. 

C, =0.400—for pipe made of wet-mix concrete by the 
cast and vibrated methods. Pipe units 
must be at least 12 ft. long and the in- 
terior joints carefully finished by hand 
troweling and evenly washed with cement 
mortar. 


] 
> 
jee) 
Lt 
S 


SOME ES 
PLONE 


CAVA GE 


Flow, cfs 
O 


PATS SPAIN Awe 


30 40 50 10 20 
Gradient, ft. per |,OO0O ft. 


Pp Nt TATE ON NNT Ni BS 


pipelines by Scobey’s formula: Cs = 0.345. 


radient, ft. per |, 
ete pipelines by Scobey’s formula: Cs = 0.370. 


Fig. 5. Flow of water in concrete 
300 


Fig. 6. Flow of water in concr 
2000 


The Chezy-Kutter and Manning formulas* also may 
be used for the determination of head losses in con- 
crete pipelines. For application to pipe problems, the 
Manning formula usually is written in one of the fol- 
lowing forms: 


=——— d%s%, in which 
n 


s=drop in hydraulic gradient, in feet, per foot; 
n =coefficient of roughness of the pipe. 


Recommended values of n for use in the Manning 
formula range from 0.010 for the very best and smooth- 
est concrete pipe to 0.014 for dry-mix pipe with interior 
joints not finished by hand. 

The coefficients given above include allowance for 
minor curvature and gradual bends in pipelines. If ex- 
cessive curvature or sharp bends occur, additional al- 
lowances for hydraulic losses should be made, as indi- 
cated in Fig. 7. 

Hydraulic losses for specific conditions and structures 
frequently encountered in irrigation systems are listed 
in Table 1. 


*H. W. King, Handbook of Hydraulics (Third Edition), 
pages 174 and 182. 


Fig. 7. Loss of head due to bend in pipeline. 
26 


2 
Hy =Ky- 


a Single angle miter bends 


Type of lose es 2 


Taper, increasing diameter 0.15 A; 
Taper, reducing diameter 0.10 H, 
Entrance, reservoir or structure 
into pipeline t 
Exit, pipeline into structure 102s 
Tee, mainline 0.0 
Tee, side outlet 25. 
Gate valve 0.20. A, 
Propeller-type line meter 
4-in. meter, 0.0 to 0.6 cfs 1.0 ft 
6-in. meter, 0.7 to 1.4 cfs 1.0: fte 
8-in. meter, 1.5 to 2.0 cfs 0.42 ft 
12-in. meter, 2.1 to 3.0 cfs 0.20 ft 
18-in. meter, 8 to 12 cfs OL 3te 
20-in. meter, 12 to 15 cfs O L3tte 
24-in. meter, 16 to 22 cfs OU. COG 
Vertical flowmeter stand 1.0 ft 
Traveling water screen Ot its 
Constant head valve 5,0 Ait 


**These values were taken from H. W. King, Handbook 
of Hydraulics, and from Design Standards for Pipe Dis- 
tribution Systems and Closed Conduits, U.S. Bureau of Rec- 
lamation. 
+See Fig. 8. 
ttProbable maximum; use manufacturer’s recommendations. 


2 
H, = Total head lost in bend 


Ky=0.25(55) 


el 
Kp= Bend coefficient (from chart) 


V = Velocity 


aoe 
=- 


g = Acceleration of gravity =32.2 


©2 ahd 10° IS? 202 op 30° Rolot 40° 45° 
Deflection angle A 


10 


50° 55° 60° 65° 70° ag 80° 85° 90° 


10.0 


5.0 


4.0 


3.0 


2.0 


Head loss, ft. 
(=) 


0.5 


04 


0.3 


0.2 


0.1 é 4 
Fig. 8. Head losses at | 2 3 4 
entrances to pipeline. 


Fig. 9. Typical division box incorporating sharp-crested 
weir for measuring flow. 


0) 20 30 40 50 100 
V,ft per second 


Pipeline Structures 


Water Measuring Devices 


Accurate measuring assures equitable water distribu- 
tion to the users and provides good control of the appli- 
cation of irrigation water to their crops. For many years 
the simple, sharp-crested weir has been used to measure 
and regulate flows in both open-ditch and concrete pipe 
systems. Because of its simplicity, the sharp-crested 
weir probably is the most economical measuring device 
in use today. In many cases sand-trapping facilities 
have been incorporated into weir boxes. 

Under some conditions—for example, where water 
supplies are limited—weir measurements may not be 
sufficiently accurate or dependable. Mechanical measur- 
ing and totalizing meters have been developed for such 
cases. The vertical flow meter set on top of a riser pipe, 
which is surrounded by a large standpipe, is one form 
of totalizing meter for farm delivery units. Where the 
hydraulic gradient below the meter would be too great 
for an economical flow meter installation, line meters 
have been used. Regulation of the flow usually is pro- 
vided by an irrigation-type gate valve installed in the 
pipe leading to the meter stand. 


11 


Aas 


Je a St, wes 
& ae inn * x ys 4 
hes . ye iy ae ey os ‘ 
oy on e il a : S s 


Fig. 10. Baffle and flow meter stands of precast concrete 
pipe under construction. Note use of precast concrete bases 


for these stands. U.S. Bureau of Reclamation photograph 


Trash or Moss Screens 


Whenever water is taken from a reservoir or canal 
into a pipe system, floating and otherwise transportable 
debris must be removed if the pipelines are to operate 
properly. Screens may be installed either in the turnout 
structure itself or in a special screening box just below 
the turnout. To ensure ample screen area, the velocity 
through the screen is limited to about 0.5 ft. per second 
based on the gross area of the screen. Double screens 
usually are provided; this permits one to be cleaned 
while the other is being used. An installation may con- 
sist of several successive screens. In this case, each layer 
has a smaller mesh than the preceding one. Some screens 
are equipped with mechanical cleaning devices. 


Sand Traps 


Whenever excessive quantities of sand or silt are ex- 
pected to be in the water entering a pipe system, a sand 
trap should be provided at the turnout from the canal. 
Sand traps may be any type of structure that will (a) 
slow the water sufficiently to permit the transported 
material to settle out, and (b) be readily cleanable. 


Check Structures 


Baffle stands serve the same purpose in open-pipe irri- 
gation systems that check structures do in canal sys- 
tems. The essential element of a stand is the baffle wall 
that checks the hydraulic gradient to an elevation suffi- 
cient to make deliveries between the baffle and the next 
upstream control. The top of the baffle should be 0.3 ft. 
above the maximum water surface required by the turn- 
outs for which it provides checking. The stand itself 
should be high enough to provide about 2 ft. of free- 
board above the water surface at the maximum flow 
over the baffle, and should extend at least 4 ft. above 
the ground. The head required at a baffle to pass a spe- 
cific flow may be read directly from Figs. 12 or 13. 

To prevent flow of water over the baffle and thus 
minimize the possibility of surging, a gate valve some- 
times is installed near the bottom of a baffle wall as in 
Fig. 10. In operation, this gate is closed just enough to 
check the upstream water surface about to the top of 
the baffle with little or no overflow. 

Because of their simplicity and low first cost, pipe 
stands should be used for these structures whenever 
possible. Box stands are used only where a pipe stand 
would be unsuitable. Pipe stands usually do not provide 
sufficient room for installation of gates or other operat- 
ing equipment. 


Fig. 11. Traveling moss screen typical of those used in a western state. Moss and other debris is carried up the incline 
and dumped on the belt which conveys it to a waste pile at one side of the canal. 


Fig. 12. Flow of water over suppressed weir. 


Head (H) on weir, ft. 


5.0 


40 


3.0 


20 Ee r + 


05 W i 


0.4 T ] i 


=3.367LH* = 
03 i] 


S 


| zZ 3 4 5 10 20 30 40 50 100 150 200 
Flow (Q), cfs 


Fig. 13. Flow over submerged weir. 


Downstream depth in feet 


D 


7 


g = Discharge per foot of weir crest 


Curves prepared using the Herschel 

formula. See King, Handbook of Hydraulics 

(1939) pages 98-99. 
at 


= = 4 


i 


Z = Head loss in feet 


13 


Fig. 14. Typical control stand with gate valve at base of 
baffle to bypass a portion of the flow. 


The size of either box or pipe stands usually is de- 
termined by the size of the pipelines, by limiting the 
velocity of vertical flow on either side of the baffle to 
about 4 ft. per second, or by the space needed for in- 
stallation of equipment. Velocity of flow into or out of 
the stand should be limited to about 8 ft. per second. 


Fig. 15. Suggested details for air vent. 


ei 6" min. 


ca 
Hardware cloth, xa mesh 


i i 


zs £ 
a= 
ro) Asbestos cement pipe 
aw 3"dia. to |O' high 
. 4"dia.10' to 15' high 
Hydraulic 6"dia.15' to 25 high 
gradiant 


Natural ground surface 


15 max.without guy stays 
Guy stays required for heights above |5 


12"min. 


art 
4 Est min, 


: Raa s at On eet One 
L Width of trench | 


14 


Collection and Division Boxes 


A collection box should be provided at the upper end 
of a lateral pipeline when its turnout from the mainline 
or canal has more than one line of pipe. If the turnout 
flow is to be divided among several pipe laterals or 
deliveries, a division box would replace the collection 
box. A division box is also used wherever several later- 
als, each too large to be served by a tee, take off from 
the mainline. 


Vent Structures 


An air vent should be provided wherever air may ac- 
cumulate. This may occur at high points in the line or 
at breaks in grade, or downstream from a gate or valve 
where the vacuum may be high enough to overload the 
gate leaf or cause cavitation damage. Satisfactory air 
vents may be constructed of precast concrete or asbes- 
tos-cement pipe. Where venting only is required, a 6-in. 
diameter vent is adequate. However, if access to the 
pipeline is desired at this point, the vent should be at 
least 30 in. in diameter. In any case the vent should 
be high enough to provide at least 2 ft. of freeboard 
above the hydraulic gradient at that point. Vents con- 
structed at horizontal angle points in the line should 
have their bases designed to serve also as anchors or 
thrust blocks. 

For heads higher than about 25 ft. it usually will be 
more economical to use air valves than vent structures. 
These should be a type of valve that will release air 
under pressure, as well as while the line is filling. 


Gates and Valves 


Gates and valves are used to regulate the flow in 
pipe irrigation systems and to sectionalize the system 


Fig. 16. Typical air release valve. 
U.S. Bureau of Reclamation photograph 


Note: Plot based on 


Hy-H, 
Ke V 


= Cavitation index 
Hr-Hp 


ih 
| 
| 


H= Pressure head |2 dia. downstream 


H,=Total head 2 dia.upstream 


Ayy= Vapor pressure relative to 


atmospheric pressure (assumed 


to be -31 ft.) 
-—+—+ 


+ 1 


Zone A - No cavitation. No protection needed. 


+ Zone B - Mild cavitation at end of valve. Protection 
probably not needed. 


Total head upstream of value(//7) ,feet of water 


(Protective lining or sudden enlargement.) 


Zone D - Severe cavitation with damage in downstream 
pipe. Protection needed against cavitation 


moving downstream. (Sudden enlargement) 


60 80 100 120 


Pressure head below valve (46), feet of water 


Fig. 17. Cavitation characteristics of gate valves in pipelines. 


so that a break in one area will not require shutting 
down the entire system. Gate valves usually are used 
in full-pressure or semiclosed systems, and either gate 
valves or slide gates are used in open systems. Gate 
valves are somewhat more convenient to use; they mini- 
mize leakage and eliminate the need for a gate structure. 
Gate valves and the pipe immediately downstream 
from them may be subject to cavitation if the head 
differential across the valve is more than about 35 ft. 
The cavitation chart, Fig. 17, will help the engineer de- 
termine whether special treatment of the pipeline im- 
mediately downstream from the valve is needed.* 


Drains and Manholes 


Drains or blow-offs may be installed at the low points 
of pipelines to permit pumping out those portions of 
the lines that cannot be drained by gravity. Manholes 
to provide access for inspection and maintenance are 
installed at intervals of 4% to 1 mile in the larger-size 
lines. Additional manholes sometimes are provided by 
the contractor for use during construction of the line. 


Pipe Manufacture 


Concrete pipe are manufactured by three processes 
which are usually described as (1) cast-and-vibrated, 
(2) centrifugally spun, and (3) machine-made. 

*See J. W. Ball, ‘‘Cavitation Characteristics of Gate 
Valves and Globe Valves,”’ Transactions of the American Soci- 


ety of Mechanical Engineers, Vol. 79, No. 6, August 1957, 
pages 1275-81. 


Concrete used in the cast-and-vibrated process is 
quite similar to high-strength structural concrete but 
of somewhat lower slump. Density is obtained by high- 
frequency vibration, applied either to the concrete or 
to the exterior of the forms. 

The slump of concrete for machine-made pipe often 
is zero, and sometimes the concrete is even drier than 
that required for zero slump. Most unreinforced concrete 
pipe is made in either ‘‘tamped”’ or ‘‘packerhead”’ ma- 
chines, and density is obtained by actual mechanical 
compaction of the concrete. 

In the centrifugal process, density is obtained by cen- 
trifugal action, sometimes accompanied by rolling or 
vibrating. Concrete used in this process should have 
approximately zero slump to prevent segregation. 

Curing of concrete pipe is essential. Curing usually 
involves sealing the concrete surface with a membrane, 
applying moisture continuously for at least 7 days, cur- 
ing by moist steam, or by some combination of these. 
Drying out of the pipe immediately after casting and 
before curing is started must be prevented. 

Gradation of the aggregates and the proportion of 
fine to coarse aggregate probably affect the economy 
and quality of concrete pipe more than any other step 
in their manufacture. Some specifications require a min- 
imum cement content and a minimum percentage of 
coarse aggregates. 

Conformance to the applicable ASTM or federal spec- 
ification and the use of properly designed mix will en- 
sure satisfactory pipe. 


15 


‘| Zone C - Mild to severe cavitation with damage confined 
to end of valve. Protection needed near valve. 


Construction 
Bedding 


Concrete pipelines for irrigation usually are laid in 
such shallow trenches that special bedding practices are 
unnecessary. If the trench is excavated accurately to 
grade in fairly uniform soil, the pipe may be laid directly 
on the trench bottom. Some contractors prefer to pre- 
pare the trench bottom by spreading a thin (14 -in. max- 
imum) cushion of sand or fine earth. 

Wherever possible, trenches should be excavated with 
straight sides and wide enough to permit proper laying 
of the pipe and finishing of the joints. Clearance should 
be at least 6 in. on each side of the pipe for diameters 
up to 16 in. and 8 to 12 in. for larger pipe. 

Pipelines should be laid deep enough that they will 
not be displaced or damaged by volume changes in the 
foundation or backfill soil caused by variations in tem- 
perature or moisture content, or by the movement of 
farm equipment or other vehicles over the pipe. In per- 
vious soils not subject to heavy surface loads, extreme 
changes in moisture content, or deep freezing of the 
ground, a minimum cover of 2 ft. over the top of the 


Bedding 


Depth of backfill above top of 


Outside diameter ; 
conduit, feet 


of conduit, 

inches 2 4 6 8 10 
16 10.3 3.4 1h O22 Ost 

30 16.5 6.1 3.0 1.8 1st 

44 20.0 8.4 4.3 2.5 1.6 

58 ray 10:1 5.4 3.3 2. 

72 22.6 11.4 6.3 3.9 2.6 

100 23.4 1229 Tak 5.0 3.5 


Internal pipe diameter, inches 


ASTM Specifications 

Class Factor 10 12 15 18 21 24 30° 36 48 60 W72™uEedeee 
C118 Irrigation Le 0.8 6.7 6.7 7.0 7.2.73 — — — — =e 
Safety factor =1.5 C HN 8:0 9.9 99.6 9.8 9.699.592 
C76 Class II D 1h — 63 7.2 79 8.7 9.2 10.3 86 11.5131 145m ieee 
Safety factor =1.0 C ten — 8.8 10.3 11.2 12.0 12.8 13.9 12.9 14.7 16.3 17-6eioseeee 
Wall B B B B B B B B SB Bee 
C76 Class III D ball — 8.7 9.8 11.0 11.8 12.5 13.7 12.7 14.7 16.3 17.8616 meee 
Safety factor =1.0 1.5 — 14.3 16.5 18.2 19.2 20.0 20.7 17.1 19.7 21.1 22.3523 ;q—eeeee 
Wall B B B B B B B B B Ga 
C76 Class IV a — 17.7 20.6 22.4 23.1 20.7 22.5 18:4 20.6 22.4 247] =ope 
Safety factor =1.0 C 1.5 — *NL NL NL NL NL 82.8 28.3 30.4 31.8 33.1330 
Wall B= B. (BS %7Bs (CoMC 35C8 CaO ae re 


*NL=No limit to bottom of pipe. 


This table was computed by the Marston formula, We— Cr Bas 


for C118, 0.01-in. crack for C76) 


Allowable load on pipe was based on pipe strength (ultimate 


divided by the safety factor indicated and multiplied by the bedding factor. Trench width 


of top of pipe assumed = B, + 16 in. for internal pipe diameters up to and including 33 in., and B, + 24 in. for internal diam- 


eters greater than 33 in. (B, external diameter of pipe.) 


16 


pipe is recommended. In heavier soils subject to volume 
change due to freezing or changes in moisture content, 
it is advisable to provide a minimum cover of 3 to 5 ft. 

Unless the pipeline is located under a road or rail- 
road, any of the classes of pipe discussed in this booklet 
probably will be strong enough if reasonable care is 
exercised in bedding and backfilling. Table 2, based up- 
on the Marston formula for various classes of pipe 
bedding, shows the approximate permissible depths of 
cut to bottom of concrete pipe. The values given in 
these tables were computed on the strength of the con- 
crete pipe, as determined by the three-edge-bearing test, 
multiplied by a load factor that depends on the class of 
bedding used, and divided by the indicated safety factor. 

In addition to the weight of the backfill material, any 
load on the surface over the pipe increases the load on 
the pipe. Table 3 gives the percentage of such loads 
transmitted to the pipe for various diameters and 
depths of embedment. This table was prepared by use 
of the formula and methods described by Spangler and 
Hennessy. * 

Note that except for large conduits the percentage of 
load transmitted to the pipe is insignificant if the depth 
is greater than 6 ft. Where the surface loads are rather 
heavy, as when a relatively shallow pipeline is under a 
highway or railroad, they should be added to the back- 
fill load to determine the required class of pipe and 
bedding condition.** 


Joints 


Proper jointing of precast concrete pipelines is one 
of the most important steps in the construction of a 
satisfactory irrigation system. Cement mortar is most 
commonly used for joining short lengths of the smaller- 
size plain or reinforced concrete pipe. Some type of rub- 
ber gasket usually is used to seal joints in pressure lines, 
low-head lines with 6-ft. or longer sections and asbestos- 
cement pipelines. 

Mortar Joints. The great majority of all mortar 
joints in concrete pipelines are made by a rather well- 
established procedure that involves spreading cement 
mortar on the two sections of pipe, forcing them to- 
gether, and completing the joint by interior wiping or 
brushing and exterior banding. In recent years pneu- 
matically applied mortar joints have become popular, 
and special equipment for making such joints has been 
made available. Another recent development in this 
field involves pouring cement grout into a fabric diaper 
which is wrapped completely around the pipeline at the 
joint location. The grout should be poured from one 
side until it has flowed under the bottom of the pipe, 


*M. G. Spangler and R. L. Hennessy, “‘A Method of Com- 
puting Live Loads Transmitted to Underground Conduits,”’ 
Highway Research Board Proceedings, Vol. 26. For a more 
detailed discussion of loads on underground pipelines, see 
Concrete Sewers, pages 22-23, available only in the United 
States and Canada on request to the Portland Cement As- 
sociation. 


**See M. G. Spangler and R. L. Hennessy, ‘“‘A Method 
of Computing Live Loads Transmitted to Underground 
Conduits.”’ 


then from the opposite side to fill the diaper completely. 
The porous diaper fabric permits the escape of air and 
excess water from the mortar. The resulting joint is 
dense, free of voids and watertight. 

The procedure for laying pipelines with ordinary mor- 
tar joints has developed from experience over the years. 
It is used with only slight modifications by most ex- 
perienced contractors. 


« 


Fig. 18. Constructing pneumatically applied mortar joint 


in 42-in. pipeline. U.S. Bureau of Reclamation photograph 


> oe aed its. ne Be 


Fig. 19. Constructing diaper joints in 42-in. pipeline. Note 
band reinforcement of wire fabric. Diaper joints are hand 


finished at the top of the pipe. 
U.S. Bureau of Reclamation photograph 


bg 


*, << 


ao Re 


Fig. 20. Groove end of concrete irrigation pipe is filled 
with portland cement mortar. Workmen should wear rub- 
ber gloves to protect their hands. 


The sections of the pipe are unloaded along the trench 
and then tilted into it, groove end up. The tongue end 
of the pipe section already in place is cleaned and 
wetted, and mortar for making the exterior band is 
placed in a depression made in the subgrade at the 
joint location. 

The groove end of the next section of pipe to be laid 
is wetted and filled with laying mortar. The pipe is then 
tipped over carefully so as not to dislodge the mortar 
and is shoved over the tongue end of the pipe previ- 
ously laid to make a snug fit. Mortar is squeezed out of 
the joint on both the inside and outside of the pipe. 
Because extruded mortar would obstruct the flow of 
water, the inside of the pipe is brushed smooth of any 
surplus mortar with a long-handled brush. This is done 
after the pipe is placed true to line and grade. 

External bands of mortar should be used at all mortar 
joints in concrete pipelines. They should completely sur- 
round the pipe, and should be not less than % in. thick 
at the joint and feathered out for approximately 2 in. 
oneach pipe section. The workman who puts on the 
bands customarily works not less than two nor more 
than five sections back of the men who lay the pipe. 
This is to make sure there will be no movement of the 
pipe after the band is applied, since such movement 
would loosen or crack the band. The area to be covered 
by bands is cleaned and wetted; then the mortar is ap- 
plied and pressed down over and into the joints. Mortar 
for the bands should be applied and pressed firmly into 
place by hand to secure a thorough bond between the 
pipe and the band. Rubber gloves are worn to protect 


the hands. The band is finished by brushing or light 
troweling. 


18 


TS aad 


Fig. 21. Pipe with groove end filled with mortar is shoved 
up tight over tongue end of previously laid pipe section. 


Tongue end of pipe has been cleaned and wetted. 
University of California photograph 


ee 


Fig. 22. Mortar bands are finished by light troweling or 
by hand. 


Cement for laying and banding mortar should com- 
ply with current ASTM Standard Specifications for 
Portland Cement (C150) or Standard Specifications for 
Air-Entraining Portland Cement (C175). The mortar 
is composed of not less than 1 part cement to 2 parts 
of clean, well-graded sand that will pass a No. 8 sieve. 
Hydrated lime, fire clay, diatomaceous earth, or other 
suitable inert material may be added in a quantity not 
to exceed 10 per cent of the cement by volume. The 
laying mortar should be of such consistency that it will 
adhere to the ends of the pipe and be squeezed out of 
the joint when the pipe sections are placed together. 

The mix for the banding mortar should be the same 
as that specified for laying mortar. It should be plastic 
and of such consistency that the band will adhere to 
the side of the pipe. The external surface of the pipe 
should be cleaned and wetted to ensure proper bond 
with the band. There should be a continuous union be- 
tween the joint mortar and the band mortar. 

As the pipeline is completed it is given an initial 
covering of moist, fine earth or sand to protect the 
joints from drying and to help the mortar cure properly. 
The covering is applied carefully to avoid injury to the 
fresh mortar joints and is from 6 to 12 in. deep over the 
pipeline. All openings in the pipeline are covered with 
burlap or paper and then with moist earth or sand. This 
prevents drying of the joint mortar by circulation of air 
within the line. For the same reason, the line is sealed 
at the end of the day’s work. Water should be placed in 
the pipeline within 36 to 72 hours after laying so that 
the line will expand while the mortar joints are still green. 

A very small percentage of unreinforced concrete pipe 


irrigation systems have been damaged by longitudinal 
splitting along the top and bottom of the pipeline or by 
circumferential cracks in the mortar joints. Longitudi- 
nal splitting usually is caused by excessive longitudinal 
compression. These compressive stresses are induced in 
the line by wetting of the concrete. Longitudinal split- 
ting usually has occurred in desert areas where the pipe 
have been laid in an extremely dry condition or have 
been permitted to dry out after laying but before water 
is introduced into the line. 

On the other hand, circumferential cracking is caused 
by the longitudinal tension that results when a pipeline 
is allowed to dry out during the nonirrigation season or 
when unusually cold water is turned into the line. 

Long experience with the construction and operation 
of pipe irrigation systems indicates that these two types 
of trouble can be prevented by observing the following 
rules in their construction and use: 

1. Use moist soil for initial backfill, as described in 

detail in the preceding section. 

2. Minimize air circulation through the line by proper 
design and operation and by keeping all openings 
covered whenever possible, both before and after 
the pipeline is placed in operation. 

3. Put water into the line as soon as possible, but not 
under pressure, and if possible keep water in the 
line when it is not being used for irrigation. 

4. Do not use expansion joints or other construction 
features that might eliminate longitudinal com- 
pression. Adherence to the first three rules listed 
above will ensure that such compression will not 
be excessive. 


Fig. 23. Constructing 42-in. diameter reinforced concrete pipeline with rubber gasket joints. 
U.S. Bureau of Reclamation photograph 


to 


Rubber Joints. In recent years rubber gasket joints 
have been increasing in popularity for use in concrete 
pipe irrigation systems. Several types of rubber joints 
have been developed and used, all of them depending 
for sealing action on the compressing effect of two con- 
centric cylindrical surfaces—bell-and-spigot or tongue- 
and-groove—on the rubber gaskets. Some of these joints 
provide grout spaces inside or outside the pipe, or at 
both locations. For small-diameter pipe the inside grout 
space usually is filled by buttering the end of the pipe 
in place before the next section is laid. The excess mor- 
tar squeezed from the joint is wiped off and removed 
from the pipe. 

Each joint should be carefully checked after comple- 
tion to make sure that the rubber gasket is properly 
seated and has not been forced out of its proper position. 
With some types of joints, the position of the gasket 
can be checked from the outside by inserting a small 
metal ‘‘feeler’’ into the annular space between the bell 
and spigot. 


Backfilling 


Trenches may be completely backfilled immediately 
after jointing of the pipe, while the mortar joints, if 
used, are still plastic. If backfilling is not completed 
then, it should be postponed for at least 24 hours after 
completion of the jointing operation. The backfill should 
be placed carefully on each side of the pipe simultane- 
ously to avoid lateral displacement of the pipe and pos- 
sible damage to the joints. 

Backfill may be compacted, puddled or consolidated 
by vibration. Material containing too much clay cannot 
be puddled or vibrated but must be compacted by me- 
chanical tamping or rolling. The material should be de- 
posited in horizontal layers not more than 6 in. thick 
after compacting. Compacted backfill to qualify as 


Fig. 24. Compacting previous backfill by jetting and vibrat- 


ing. Note excess of water in backfill being placed. 
U.S. Bureau of Reclamation photograph 


20 


Class B or Class C* must be of granular materials. Non- 
granular backfill, even though compacted or puddled, is 
adequate only for Class D bedding and backfill. 

Silt or silty sand may be compacted by puddling, but 
since such material is not granular and does not com- 
pact to a high density under puddling action, this pro- 
cedure likewise is adequate only for Class D bedding 
and backfill. The material is deposited in the puddle or 
pond of water in layers approximately equal in eleva- 
tion on the two sides of the pipe. During the puddling 
process the material should be agitated with poles, 
shovels or other tools so that complete filling is obtained 
between the pipe and the natural soil. The depth of 
water in the pond should not exceed 1 ft. During the 
puddling process care should be taken to prevent float- 
ing or lateral displacement of the pipe. 


Fig. 25. Compacting backfill around 84-in. reinforced con- 


crete pipeline with vibratory rollers. 
U.S. Bureau of Reclamation photograph 


Where conditions are such that the quality of bedding 
and backfilling materially affects the structural design 
and hence the cost of the pipe (usually the case when 
large-diameter pipe are installed in deep trenches), con- 
sideration should be given to the use of consolidated 
rather than compacted or puddled backfill. Free-drain- 
ing sandy or gravelly soils may be readily consolidated 
to high density by vibration, and the resultant bedding 
often is comparable with concrete cradle bedding, Class 
A. An advantage of the consolidated backfill method is 
that no shaping or other preparation of the foundation 


*See Concrete Sewers, page 24, available free on request 
to the Portland Cement Association only in the United 
States and Canada. 


is required because the materials can be flowed around 
and under the pipe by this process. In some cases, de- 
pending on the availability of materials and size of the 
job, contractors have elected to use consolidated back- 
fill materials and procedures because of their economy, 
even though compaction by tamping or puddling was 
permitted.* 

Internal vibrators generally are used to consolidate 
backfill. The depth of layers after consolidation is usu- 
ally limited to the penetrating length of the vibrators. 
The materials must be thoroughly saturated as they 
are vibrated. The minimum density requirement for this 
method usually is specified as 70 per cent relative den- 
sity.** Higher density requirements may be specified 
for fine sands. Proper selection of materials is important 
for successful results. Excessive amounts of silt and clay 
will plug the voids between the sand and gravel particles 
and thus prevent drainage during vibration. 


Jacking Concrete Pipe 


Pipe must occasionally be installed under a highway 
or railroad without interruption to traffic. This may be 
done by tunneling or by jacking concrete pipe beneath 
the roadway as the face material is excavated either by 
augering or by men working inside the pipe. Concrete 
pipe up to 96 in. in diameter have been successfully 
installed by this method.t 


*Additional information on this process will be found in 
“Experiences with the Consolidation of Pipe Bedding by 
Vibration on the San Diego Aqueduct”? by W. G. Holtz, 
published in Second Pacific Area Meeting Papers, ASTM 
Special Technical Publication No. 206, 1957. 

**See ASTM Designation D653, Standard Definitions of 
Terms and Symbols Relating to Soil Mechanics. 

tFor more details see Jacking Reinforced Concrete Pipe- 
lines, available free on request to the Portland Cement As- 
sociation only in the United States and Canada. 


fe 7 e 


g 
= Ses fal 
Fig. 26. Jacking 42-in. diameter reinforced concrete pipe 
under railroad. 


U.S. Bureau of Reclamation photograph 


Fig. 27. Placing 12-in. diameter asbestos cement pipeline 
for irrigation system. 


Asbestos-Cement Pipe 


For many years asbestos-cement pipe, particularly in 
the smaller sizes, have been used in municipal water 
supply systems. Their economy and successful perform- 
ance in that field prompted their use in some of the 
smaller-diameter, high-pressure irrigation lines, partic- 
ularly where sprinkler systems were operated directly 
from the underground pipe system. Asbestos-cement 
pipe have proved to be appropriate for such uses be- 
cause of their light weight, fast installation with rubber 
gasket coupling, permanent high carrying capacity, and 
high resistance to corrosion and electrolytic attack. As- 
bestos-cement pipe have been used recently for portions 
of several full-pressure pipe irrigation systems. 


Testing Pipe Systems 


Pipe systems, or portions of systems, may be tested 
under the full design working pressure, or at some lesser 
pressure in the case of very high pressure lines. Lines 
made with cement mortar joints or those that include 
cast concrete structures or appurtenances should not be 
tested until at least 7 days after installation of the joints 
or the concrete. The pipeline should be filled with water 
and permitted to stand full for about two weeks to sat- 
urate the pipe thoroughly before the test. The test 
period should be 24 hours, during which time the water 
pressure should be maintained constant. Leakage dur- 
ing a 24-hour period from lines jointed with rubber 
gaskets should not exceed 200 gal. per inch of internal 
diameter of pipe per mile. Leakage from mortar-jointed 
lines should not exceed 300 gal. per inch of internal 
diameter per mile. Any leaks that show up should be 
repaired regardless of the observed rate of leakage. 
Seasonal cold water should not be used for making 
these tests. 


21 


Fig. 28. Completing a large control structure with multiple connections. 


Concrete for Structures 


Concrete suitable for pipe irrigation structures and 
appurtenances is little different from that required for 
culverts, bridges, or other structures. It should be a 
properly designed air-entrained mix of structurally 
sound and well-graded aggregates with a portland ce- 
ment paste having a water-cement ratio of not more 
than 6 gal. of water per sack of cement. For concrete 
that may be exposed to runoff water draining from irri- 
gated land, which would be the case with most irrigation 
structures, the use of Type II cement is recommended 
for improving the resistance of that concrete to sulfate 


22 


attack.* Proper placement of the concrete in the forms 
and adequate consolidation by vibration or other means 
cannot be overemphasized. All concrete or cement mor- 
tar used in the construction of pipe systems should be 
properly cured and protected against freezing so that 
it may attain the maximum possible strength, durability 
and watertightness. * * 

*Type II modified portland cement, complying with 
ASTM Standard Specification C150, is intended for use 
where sulfate concentrations are higher than normal. 

** More complete information on this subject is contained 
in Design and Control of Concrete Mixtures, available free 


on request to the Portland Cement Association only in the 
United States and Canada. 


ADDITIONAL REFERENCES 


“Canals and Related Structures,’’ Design Standard No. 
3 of Reclamation Manual, Bureau of Reclamation, U.S. 


Department of the Interior, Washington, D.C., April 
1952. 


Concrete Pipe for Irrigation, by Arthur F. Pillsbury, 
Circular 418 (1952), College of Agriculture, University 
of California, Davis, Calif. 


Irrigation with Concrete Pipe, Portland Cement Associa- 
tion, 1952. 


Lining Irrigation Canals, Portland Cement Associa- 
tion, 1957. 


Linings for Irrigation Canals, Bureau of Reclamation, 
U.S. Department of the Interior, Denver, Colo., July 
1952. 

‘Use and Economy of Concrete Pipe Irrigation Sys- 
tems,’ by A. B. Reeves, Proceedings, American Society 
of Civil Engineers, Volume 81, Separate No. 622, 
February 1955. 


23 


24 


The activities of the Portland Cement Association, a national organization, 
are limited to scientific research, the development of new or improved 
products and methods, technical service, promotion and educational effort 
(including safety work), and are primarily designed to improve and extend 
the uses of portland cement and concrete. The manifold program of the 
Association and its varied services to cement users are made possible by the 
financial support of over 70 member companies in the United States and 
Canada, engaged in the manufacture and sale of a very large proportion 
of all portland cement used in these two countries. A current list of member 
companies will be furnished on request. 


The drawings in this publication are typical designs and should not be 
used as working drawings. They are intended to be helpful in the prepara- 
tion of complete plans which should be adapted to local conditions and 
should conform with legal requirements. Working drawings should be pre- 
pared and approved by a qualified engineer or architect. 


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Today many communities are discharging raw sewage into a 
water course or lake, endangering their own or their down- 
stream neighbors’ source of water supply. Not only does this 
practice create a grave health hazard—it has many other harm- 
ful effects. Look at the damaging results of water pollution 
shown in the sketch below and judge whether any community 
can afford the price it must pay for lack of adequate sewage 
treatment facilities. 


Hea adhe Patra heen Wik ae Sewn N sac Ne hepevare | 


ruined recreational areas 
x | ! 


decreased industrial | 
water supply 


IRS ese Oe ore sins eRe OW 


Water pollution... 

* creates a serious health hazard. Sewage contains 
bacteria in large numbers, some of which are extremely 
dangerous, such as those causing typhoid fever, cholera 
and dysentery. Some scientists believe that such dis- 
eases as polio and undulant fever may also be trans- 

| mitted by contaminated water. 
| * makes the water offensive to sight and smell. 

* injures fish and wild life. Pollution reduces the sup- 
ply of oxygen in the water to such an extent that fish, 
shrimp, clams, oysters and other aquatic life cannot 


survive. Wild life such as animals and birds shun pol- 
luted waters because their feeding areas are destroyed. 

° destroys such recreational uses of water as swim- 
ming and boating. 

° may force industry to find new locations because of 
excessive cost of water processing. 

° reduces the value of waterfront property because of 
noisome odors and unsightly deposits. 

Finally, because of pollution another body of water 
is made useless at a time when our nation is striving to 
conserve its water resources. 


; 
sewage treatment benefits the community | 
, 


In dramatic contrast with the incalculable damage expansion and decentralization, | 
done by polluted water are the many benefits—both often depends on a town’s ability 
direct and indirect — that sewage treatment facilities industries. And industries give to 
offer to a community’s health and welfare. clean, healthful environment. Son 
umes of clean water for processing 

Sewage treatment... When they have to treat their ow 
° protects public health. Concentration of population will naturally select areas where 4 
brings with it the problem of public health protection. imum. Towns without adequate sey 
Even when treated, no water supply is absolutely safe ities cannot compete with towns th: 
if it comes from grossly polluted waters. When pollu- ° provides recreational activities, 
tion becomes excessive and water treatment facilities the product of modern society—h; 
are overloaded, there is grave danger of epidemics. demand for recreational activitie 
Sewage treatment protects surface and ground water lakes invite fishing, boating and sy 
supplies — both the community’s and its downstream ° conserves all forms of wild lit 
neighbors’. essential for wild life propagation. 
° stimulates community growth. People are attracted Because of these—and many othe 
to a community where their health is protected by a communities have found that stop} 
safe supply of water. only an obligation to their neighbor’ 


* attracts desirable industry. In this era of industrial happier, healthier, more prosperou: 


This 3-million-gal. sewage treatment plant in Panama City, F | 
consulting engineers, Jack: 

From the left, pairs of tanks a 

primary settling and digesters. Slud; 

while bar screer 


how a sewage treatment plant works 


A Sewage first passes through a bar screen that catches large objects such as 
rags and sticks. & ] 

B Next, the liquid flows slowly through a grit chamber, allowing sand and gravel a2 Simplified lay 
to settle. of one type 

C The liquid then moves to a settling tank, where the solids settle to the bottom sewage treatment ple 
and are referred to as “sludge.” | 

D The sludge is pumped to a tank for digestion. q 

E After a period of time, the digested sludge is deposited on drying beds. After 
drying, it may be burned, buried, or used for fertilizer. 

F The liquid from the primary settling tank is pumped or allowed to flow by 
gravity to a trickling filter, where it is sprayed on a bed of coarse rocks. 

G After passing through the rock filter, the liquid flows to a secondary settling 
tank to remove any remaining solids. 

H_ Finally the liquid may be chlorinated to kill any remaining bacteria before 
it is discharged into the receiving stream. 


In some cases, it may be possible to discharge the liquid directly into the 
receiving stream after it has passed through the primary settling tanks ( step 
C), and received chlorination (step H). This is known as “primary” treat- 
ment. However, complete treatment is usually required. 


Note: Factors ¢ 
of sewage treatme 
type and quantity 

| 


- growth 
desirable 
tion to a 
arge vol- 
erations. 
yply they 
at a min- 
ent facil- 
ive them. 
re time— 
a greater 
vers and 


aters are 


| benefits, 
ion is not 
ntial to a 


y life. 


1 by Smith and Gillespie, 
nt into operation in 1953. 
y settling, trickling filters, 
ds are in the foreground 
- photograph to the right. 


the cost is low 


The cost of sewage treatment depends on the kind of 
treatment needed, and on the cost for local materials 
and labor. According to the U.S. Public Health Service, 
study of a typical state showed that sewage treatment 
facilities cost, on the average, about five cents per day 
per family. This is a modest price to pay to rid a com- 
munity of the deadly effects of pollution. 


= j 
; , . se oi Ge 
pam Eels: 


ve engineer in selecting the best type Bors maar 
community include cost, population to be served, ae s 
Is the condition of the receiving stream. 


\/ 


v2 


what can you do? 


To assure that your community will have adequate facil- 
ities to safeguard health and welfare, cooperate with 
your city officials by letting them know you favor con- 
struction of a sewage treatment plant. Secure active 


newspaper support. Work through your local clubs and 
civic groups to arouse public opinion to the necessity 
of ridding your community of the danger of pollution— 
once and for all. 


PORTLAND 
CEMENT 
ASSOCIATION 

33 West Grand Avenue 
Chicago 10, Illinois 


The activities of the Portland Cement Associa- 
tion, a national organization, are limited to 
scientific research, the development of new 
or improved products and methods, technical 
service, promotion and educational effort (in- 
cluding safety work), and are primarily de- 
signed to improve and extend the uses of 
portland cement and concrete. The manifold 
program of the Association and its varied serv- 
ices to cement users are made possible by the 
financial support of over 70 member companies 
in the United States and Canada, engaged in 
the manufacture and sale of a very large pro- 
portion of all portland cement used in these 
two countries. A current list of member com- 
panies will be furnished on request. 


Printed in U.S. A. 


Atlanta 3, Ga. 


Chicago 2, Ill. 


Des Moines 9, lowa 


For further information on sew 


507 Mortgage Guarantee Bidg.. 3 
Austin I, Texas 110 East Eighth St. aS 
Baltimore 2, Md. «512 Keyser Bldg. 
Birmingham 5, Ala. 1214 South 20th St. 


Boston 16, Mass. 20 Providence Ste ieien 

4 West Washington St. oe 
50 West Broad St. ee 
721 Boston Bldg. 

408 Hubbell Bldg. 
Helena, Mont. — Mezzanine—Placer Hotel ee 
Indianapolis 4, Ind. 612 Merchants Bank Bldg. 
Kansas City 6, Mo. 811 Home Savings Bldg. 
Lansing 8, Mich. 2108 Michigan National Tower 


Columbus 15, Ohio 
Denver 2, Colo. 


? 


Los Angeles 17, Calif. 816 West Fifth Sh eee 
Louisville 2, Ky. © = 805 Commonwealth Bldg. 
Memphis 3, Tenn. 916 Falls Bldg. a. ae a 


% 


Copyright 1958 by Portland Cement Astociotive ; gee 


_ Milwaukee 2, Wis. 
Minneapolis 2, Minn. _ 
New York 17,N.Y. 
Oklahoma City 2, Okla. 
_ Omaha 2, Neb. 
Orlando, Fla, 
Philadelphia 2, Pa, 
Portland 3, Maine 
~ Richmond 1 


ge treatment plant 


cS 


write to the nearest Portland Cement Association 


p12 ta. 


9, Va. 


C-104 


CEMENT MORTAR LININGS FOR IRON PIPE 


Portland Cement Association 
33 West Grand Avenue 
Chicago 10, Illinois 


May 1953 


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CEMENT MORTAR LININGS FOR IRON PIPE 


American experience with cement-lined iron pipe 
began in the eastern states over a century ago. In an effort 
to prevent corrosion of water mains, thin sheet iron pipes 
about 1/16 in. in thickness were coated on the inside and 
outside with a 1/2-in. to 3/4-in. thickness of cement 
mortar. In spite of their structural deficiency, some 
sections of this coated pipe were found in excellent con- 
dition with unimpaired carrying capacity after more than 
70 years of service. 

It was not until 1921 that an attempt was made to 
line cast-iron pipes with cement mortar. Experience and 
tests to date indicate that there has been no impairment of 
the carrying capacity of these pipes, even in areas where 
highly tuberculating water is handled, 


The principle advantage of lining ferrous pipe 
with cement mortar is to prevent corrosion which impairs the 
Guality of the water and reduces carrying capacity of the 
pipe lines through tuberculation. Untreated iron corrodes 
in water by pitting. Over each pit a tubercle is formed by 
the reaction of the dissolved iron and the oxygen in the 
water in combination with iron bacteria. This tubercle in- 
creases to many times the size of the pit. This condition 
decreases the cross-sectional area of the pipe and increases 
the friction loss, which in time reduces carrying capacity 
and increases pumping costs. The loss in capacity may often 
amount to as much as 30 to 50 per cent or more in 15 years. 
Portland cement mortar linings provide a smooth covering that 
(1) prevents incrustations on the pipe interior, thereby 
maintaining its original cross-section, and (2) mitigates 
taste, odor, and plumbing stain. 


When metal pipes in contact with water undergo 
corrosion some of the metal goes into solution with the 
water causing sediment to form and increasing the turbidity 
of the water, especially in dead ends. Small quantities of 
iron rust in the water will impart a discoloration which 
stains plumbing fixtures, and clothing. Taste is affected 
when the concentrations of iron solutions in water are 
approximately 0.5 to 2 ppm. Odors are usually caused by 
bacteria that reduce the sulphates in water to hydrogen 
sulfide. This results in a rotten-egg odor in dead ends, 
even though the raw water contains no appreciable amounts 
of hydrogen sulfide. 


The elimination of tuberculation in cement-lined 
pipe is a distinct advantage in the design of the distribution 
Systems. The friction coefficient "CC", used in the Hazen and 
Williams formula, remains at 140 instead of being reduced to 


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70 or &0 by tuberculation over a period of years. There- 
fore, it is unnecessary with cement-lined pipe to use a 
larger diameter to compensate for reduced cross-section 
and increased friction loss during the life of the pipe. 
While the first cost of a lined pipe may be more than an 
unlined pipe, over a period of years the lined pipe will 
be found the more economical if pumping, maintenance, 
interest and depreciation costs are considered. 


Cement-mortar linings will prevent leakage from 
small holes in iron pipe caused by electrolytic action. 


Experiments by the City of Detroit have shown that 
3/8-in. cement mortar linings in a 4@-in. diameter steel 
pipe effectively sealed small openings up to 4-in. diameter 
under pressure of 300 psi; in these same experiments 5/8-in. 
thickness linings were effective in sealing openings up to 
6 in. in diameter under the same pressure. 


Thickness of Linings 


The American Standard Specifications for Cement 
Mortar Lining for Cast Iron Pipe and Fittings (A21.4-1953), 
gives the following reguired thickness for cement mortar 
iiningss 


Inside Diameter Minimum Thickness 
opel ge lays! of. Linin Hr 
BieeO, hicpeil. 1/8 in< 

WA ener 275) ceate 3/16 in. 
SiO) aon WAST Mech alee Dh Ay alain 


A plus tolerance of not more than 1/8 in. is permitted on all 
sizes of pipe, and not more than 1/4 in. on all sizes and 
patterns of fittings. 


Mixture 


The cement lining not exceeding iy as ins.) in) thickness 
usually consists of a mixture of one part of portland cement 
to one or one and a half parts of sand, by weight. The sand 
must be clean, of good quality and well graded with 100 per 
cent passing a sieve having a clear opening equal to one-half 
the minimum thickness of the lining and with not more than 
5 per cent passing No. 100 mesh sieve. 


Applying Cement Mortar Linings to New Pipe 


Application of mortar linings to new pipe is 
usually done by the pipe manufacturer. The pipe is scraped 
to remove any projections which might protrude through the 
lining and then is thoroughly cleaned by wire brushes and 


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rubber squeegees. A measured amount of cement mortar is 
inserted into the pipe. The pipe is then vibrated and 
rapidly spun at peripheral speeds up to 600 ft. per 
minute. This compacts the lining, giving it a dense, 
smooth surface of uniform thickness. Special methods for 
lining fittings have been developed. All parts of the 
lining should be kept constantly damp for at least 24 hours 
after the lining is placed and as much longer as may be 
necessary to control separation and cracking. In some 
instances a membrane seal coating is applied as a curing 
medium, 


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Applying Cement Mortar to Old Pi 


The problem of restoring the capacity of existing 
water mains lost through tuberculation, has resulted in 
increased interest in lining old pipe lines. Cleaning alone, 
while temporarily effective, will not prevent recurrence of 
capacity loss nor will it preserve the life of the pipe. 
Cement lining applied at the time of cleaning will do both. 


Old pipe lines 16 in.,and greater, internal 
diameter have been lined-in-place py the following methods. 
Openings in the pipe lines to permit access of the workmen 
and machines are made at intervals of 500 to 1,000 ft. by 
removing 6- to 10-ft. sections of pipe. Pipes are cleaned 
by mechanical grinders or metal scrapers followed by wire 
brushes. Pipe lines 24 in. in diameter and over are then 
lined with cement mortar by an electrically driven machine 
which travels through the pipe. After mixing on the surface, 
the mortar is then delivered to the lining machine in the 
pipe by various methods depending upon the diameter of the 
pipe. For pipe lines of 36-in. diameter or greater, 
specially designed manually operated buggies can be used. 
For pipe lines 24 to 36 in. in diameter, the mortar is con- 
veyed by electrically power-driven buggies. These have 
also been used in larger diameter pipe. Cement mortar is 
then fed at a constant rate through the lining machine which 
throws the mortar against the walls of the pipe. The thick- 
ness of the lining can be controlled by the speed of the 
machine. The lining machine is equipped with revolving steel 
blades which trowel the mortar on walls to a smooth finish. 


Since 24-in. diameter pipe is about the smallest 
the average man can work in, a specially designed machine has 
been developed which operates by remote control for lining 
in place pipe as small as 16 in. in diameter. Mortar is 
pumped to this lining machine through a hose. The speed of 
the machine and the rotation of the head and trowels are 
controlled from the surface. Surplus or deficiency of 
mortar at the machine is indicated to the operator on the 
surface by a signal device. Thus positive control is assured 
for maintaining a uniform thickness of lining. 


ia 


Curing of the lining is effected by immediately 
closing a completed section to the circulation of air and, 
as soon as the mortar has hardened sufficiently, filling the 
pipe with steam or water or in the larger diameter pipe by 
covering the lining with a suitable liquid membrane sealing 
compound. Curing should continue for at least 24 hours, 
after which the pipe may again be placed in service. 


Old pipe lines 24 in. internal diameter and less 
have been lined successfully by exhuming and applying the 
mortar lining at a central plant by methods and machines 
Similar to those used in lining new pipe. The method used 
at Atlanta, Ga., is described by Paul Weir, general manager, 
Atlanta Water Works, in an article "New Linings for Old Pipe", 
published in WATER WORKS ENGINEERING, June 17, 1942. 


Pipe lines of 4- to 1l4-in. internal diameter have 
been lined in place by the following method. Openings 4 to 
6 £t. in length at intervals of 200 to 500 ft. are made in 
the pipe line through which cleaning and lining machines can 
be inserted and removed. All corporation cocks are removed 
and plugs screwed into taps. All valves are removed and legs 
of tees and crosses plugged. The line is then thoroughly 
cleaned by scrapers and brushes pulled through the pipe by a 
cable or forced through by water pressure. After this a prover 
is drawn through the pipe so that the pipe is clear of all 
obstructions. A predetermined amount of portland cement 
mortar of proper consistency is then placed in the line. Next 
a mandrel of proper size is drawn through the pipe at the rate 
of 12 to 20 ft. per minute. This steel, tapered mandrel 
forces the mortar against the walls of the pipe at a con- 
siderable pressure. Bends and other special fittings are 
lined by mandrels designed for that purpose. The day after 
the lining has been placed the pipe can be put back into 
service. 


Conservation Bureau 


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Bibliography 


1909 Patent or onatian Ball, granted Dec. 15, 1843, 
New England Water Works Proceedings, Vol. 23, 
Wier Ud. 


1926 LD SOL dire tis 5 
"Experience with Cement Lined Cast-Iron Pipe," 
Journal, American Water Works Association, 
WOU. LO, pecker: 
October 1926 


1938 Harkness, Bruce, 
"Cleaning and Cement-Lining Existing Water Mains 
Aion econ 
Water Works and Sewerage, Vol. 85 No. 3, p. 182, 
March 1938 


1939 "American Standard Specifications for Cement Mortar 
Lining for Cast-Iron Pipe and Fittings," 
Serial Designation A21.4-1953. Approved by 
American Standards Association, 
January 1953 


1940 Weir, Paul, 
"The Effect of Internal Pipe Lining on Water Quality," 
Journal American Water Works Association, Vol. 32, 
Deel DA 7 
September 1940 


sBSp Ags Jones, Seaver, H., 
"Development of Cement Lining for Water Mains," 
Journal American Water Works Association, Vol. 33 
ie hy RR 
October 1941 


1942 Wein, Paul, 
"New Linings for Old Pipe," 
Water Works Engineering, Vol. 95, p. 650, 
June 17, 1942 


1946 Wolfe, Thomas F., 
"Advantages of Cement Linings for Cast-Iron Pipe," 
Journal American Water Works Association, Vol. 38, 
Sip AR A 
January 1946 


1946 Jones, Gerald W., 
"Mechanically Applied Cement Mortar Used to Re-line 
31-in. Water Main," 
Engineering News~Record, 
October 17, 1946 


angt, ® A 4 nN 
. a 
, my i, 
* . ‘ 
‘ 
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. ‘ y in 
r RANE to 


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+ aah A a ed = 
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ee C re . 
; 
= 4 Goa ete ah ea F 
. i ealaii . 
ie 
qos can ae 
. i 
» oa 
Y i oH « . > 
mT . 
“ anf 
eit aed , 
| fs 
Ty: 
A oy 
. a es ars | 
Ra . . 
Cente x a4 
oo ; cre as OPS oe 
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z = 4 
. cs . ” 
ate x 
* “ a9 
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* - 
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Pp ks . ' 
"Ar ‘ 
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1947 


1948 


1949 


1949 


1949 


L949 


1950 


ao 


1950 


LJo2 


1953 


Jordan, Harry 8, 
"Costs of Corrosion to the Water Industry," 
Journal American Water Works Association, Vol. 39, 
NOW SG Ppiese libero. 
August 1947 


Lea, W.de,; 
"Discharge Coefficients for Water Pipe, their 
Preservation and Restoration," 
Water and Sewage Works, pp. 320-324, 
Sept. 1948 


Dean, John B., 
"Lining 62" and 36" Pipe Returns 13% on Cost," 
PUpESCMWOrKS Ds, 20 5 
January 1949 


Leedon, Laurie M., 
"Newark Cleans and Lines 60-in. Water Main," 
American City, 
May 1949 


Murphys iili's, 
"How Two Unique Machines Clean and Place Cement 
fimo geile ye in. Water Main, 
Pacific Builder and Engineer, pp. 60-62, 
August 1949 


Fitts, Nelson F., 
"Cement Lining and Guniting a Water Main for 
Longer Life," 
BOP eLCmuOnis «VOL HO0., Nowikiyap. 22; 
November 1949 


Moore, mews, ocears, We. H. and, Rubin, b., 
"Fundamentals of Corrosion and its Mitigation" ( A 
report of the "Committee of Developments in our 
Knowledge of Corrosion and its Mitigation" presented 
at NEWWA in 1949), 
Water and Sewage Works, p. 85, Feb. 1950 and p. 157, 
Apel 5y 


Anon., "Cleaning and Lining Mains in Place," 
Water Works Engineering, p. 220, March 1950 and p. 300, 
Aprade o> 0 


Skinker, Thomas J., 
"Pipe Lining Program at St. Louis," 
Amsrican=City p. dl, 
November 1950 


Tausig, J. Wright, 
"Cement Mortar Pipe Linings," 
FOoucne MAO d Volos, Now ty pps d5—20, 
September 1952 


Kennedy, R.C., 
"Cement-Mortar Linings and Coatings for Steel Pipe," 
Journal American Water Works Association, pp. 113-115, 
February 1953 ie 


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Copyright 1959 by Portland Cement Association 


SURFACE ESTHETICS... 


~~ 


Art and technology in architecture are re- 
turning as the most exciting architectural 
story since medieval man built the lofty 
Gothic cathedrals in Europe. This is a new 


“age of moving dynamic shapes and forms 


colorfully expressing the delight of man’s 
achievement. 

A marvel of this new age is the concrete 
curtain wall—a milestone in the evolution of 
surface esthetics in American architecture. 
These versatile and plastic surfaces, which 
combine form and color with structural ap- 
pearance, offer exciting visual experiences 
that are lacking in other less plastic and 
durable surface materials. Concrete, the 
Cinderella material of the times, offers to 
architecture a dynamic new dimension in 
the multicolored, patterned and textured 
curtain wall. Sculptural wall and panel sur- 
faces, by integration of form, function and 
material, impart new and economical trends 
to surface esthetics. 

Walls still must provide insulation and 
low-cost protection from the elements. 
However, it is now expected that walls will 
fulfill these requirements with a cross-sec- 
tion and weight reduced to new lows, com- 
mensurate with proper performance. These 


new “curtain walls’’ also have to be quickly 
and easily erected. Developing a curtain 
wall that combines these qualities has been 
a challenge for architects, engineers and 
wall panel producers. 

This booklet is intended to show how con- 
crete curtain walls combine the diverse ad- 
vantages desired in this type of construc- 
tion. Your local precast concrete wall panel 
producer will be happy to give you full 
particulars on such matters as available 
colors and textures, handling and attach- 
ment details, and costs. 

The range in shapes, sizes, designs, tex- 
tures and colors offered by concrete wall 
panels is unparalleled in this work. Not only 
are the geometric, straightline shapes and 
designs possible, but practically any free 
form can also be realized. Colors range from 
white and delicate pastels to dramatic deep 
hues sure to dramatize any structure. Tex- 
tures vary from glassy smooth to rough and 
bold. 

Concrete curtain walls ensure staunch 
protection from the elements. Many per- 
fected airtight and watertight joint details 
have been developed. Panels are securely 
attached to the structure. Fenestration can 


be designed in many ways. Excellent in- 
sulating properties minimize uncomfortable 
radiation of cold along the perimeter of the 
building and prevent expensive summer 
heat gain in modern air-conditioned towers. 

The use of lightweight concrete and per- 
fected connection details makes concrete 
wall panels easy to transport, handle and 
erect. Lifting inserts and attachment de- 
vices can be cast into the panels to minimize 
erection time and effect greatest stability to 
the connection. 

Cross-sections of concrete curtain walls 
are often narrower than those of other ma- 
terials because they require little, if any, 
backup. In many cases, the inside face of 
the panels can be left as furnished or merely 
painted. If a plaster face is desired, it can be 
applied to the inside panel surface. 

All of these factors figure in the question 
of cost. When comprehensive studies are 
undertaken of everything that affects the 
cost of several types of curtain walls, con- 
crete emerges as the one truly economical 
material. For the architect, it means that 
concrete is a newer, lower-cost curtain wall 
material offering an unprecedented freedom 
in design. 


CA pair of giouits in leyac 


Precast panels sheathe this pair of towers—the 42-story 
Southland Life Insurance Co. office building and 28-story 
Sheraton-Dallas hotel. Curtain walls on these buildings are 
similar. Sidewalls have spandrel panels with Italian glass mosaic 
tile cast in the surface. Endwall panels were cast with a mix 
containing white quartz aggregate and white portland cement 
matrix. 

Erection of the panels was simple, fast and low in cost. The 
units were simply lifted from trucks, fastened to the frame and 
the joints sealed. 


SOUTHLAND CENTER, Dallas, Texas 


ARCHITECT-ENGINEER: Welton Becket, FAIA, and Associates, Los Angeles, Calif. 
CONTRACTOR: J. W. Bateson, Dallas, Texas 
PANEL FABRICATORS: Wailes Precast Corp., Los Angeles, Calif., and Dallas, Texas 
(exposed-aggregate panels) 
McDonald Bros. Cast Stone Co., Fort Worth, Texas 
(glass mosaic faced panels) 


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In character with the fun-loving spirit of its renowned loca- 
tion, the curtain wall of this Las Vegas hotel is eye-catching in 
its panoply of colorful patterns. The multicolored aggregates in 
the precast exposed aggregate panels make this building note- 
worthy even in a city known for its self-advertising structures. 

L-shaped panels were used; windows were set in the resulting 
openings and sunshades placed above them. Only in concrete 
could panels of this unusual shape and with these brilliant 
colors be made economically. Despite a shipping distance of 450 
miles, these precast panels proved competitive. Panels were 
hoisted directly from the trucks into position on the building. 


FREMONT HOTEL, Las Vegas, Nev. 


ARCHITECT: Wayne McAllister and William Wagner, Los Angeles, Calif. 
STRUCTURAL ENGINEER: John A. Martin, Los Angeles, Calif. 
CONTRACTOR: Robert E. McKee General Contractor Inc., Los Angeles, Calif. 
PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah 


tor Luj~unisus aportmente, 


The handsome spandrel panels on this exclusive apartment 
building were erected at the rate of a floor per day. These 24- 
in. to 5-in. thick facing units were cast from about 3 to 6 ft. 
wide and in several lengths up to 24 ft. 

Alternating strips of precast exposed aggregate panels and 
windows lend pleasing horizontal lines to this 10-story building. 
Although luxurious in appointments, this structure was built 
economically. Materials costs were low and the use of a rein- 
forced concrete frame and precast wall panels made it possible 
to erect the building from foundation to roof in only 66 days. 


3660 GRAND APARTMENTS, Des Moines, Iowa 
ARCHITECT: Brooks Borg, Des Moines, Iowa 
CONTRACTOR: The Weitz Company, Des Moines, Iowa 
PANEL FABRICATOR: Mid-West Concrete Industries, Inc., Des Moines, Iowa 


Towering 28 stories over Denver is this striking bank-office 
building. Faced with Georgia white marble aggregate panels, it 
is an attention-arresting structure by day and night. Surfaces 
of the wall panels were ground to a smooth finish. 

The four-story base of the structure covers a 400 x 266-ft. plot. 
Over 100,000 sq.ft. of precast panels were used. Panels such as 
these offer the lowest maintenance available in curtain wall 
construction. 


FIRST NATIONAL BANK BUILDING, Denver, Colo. 


ARCHITECT: Raymond Harry Ervin & Associates, Denver, Colo. 
ENGINEERS: Phillips-Carter-Osborn, Inc., Denver, Colo. 
Rhuel A. Andersen, Denver, Colo. 
CONTRACTOR: Meade and Mount Construction Co., Denver, Colo. 
PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah 


10 


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Walls in banks and other financial institutions, in addition to 
fulfilling their usual practical functions, must inspire confidence 
and impart to clients a feeling of stability. In this 15-story 
bank-office building, precast concrete panels present a modern 
facade of imposing proportions. 

Although panels are lightweight and have a relatively narrow 
overall cross-section, the wall has an appearance of considerable 
depth because units were cast with a thickened crown at mid- 
panel. Staggering the positions of the units resulted in a “‘checker- 
board” pattern. From sunup to sundown, shadow patterns of the 
walls are constantly changing. Brilliance is added to the surface 
of the 3,800 panels by the white quartz aggregates. 


WACHOVIA BANK & TRUST CO. BUILDING, Charlotte, N.C. 


ARCHITECTS: Harrison and Abramovitz, New York, N.Y. 
A. G. Odell, Jr., and Associates, Charlotte, N.C. 
ENGINEER: Severud-Elstad-Krueger, New York, N.Y. 
CONTRACTOR: J. A. Jones Construction Co., Charlotte, N.C. 
PANEL FABRICATOR: Mabie-Bell Co., Greensboro, N.C. 


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The harlequin pattern of black, white and grey which key- 
notes this large shopping center is stated in its most commanding 
form on the walls of this department store. Black and white 
aggregates were mixed together for the grey portions of the 
pattern. 

Nine 8x14-ft. rectangular exposed aggregate panels per bay 
formed the triangular surface patterns. Use of lightweight con- 
crete resulted in a low shipping weight and a low “U”’ factor. 
Built-in insulation provided by the panel made it unnecessary to 
provide any backup. The result—a curtain wall with an overall 
cross-section of only 6 in. Concrete panels proved competitive in 
cost even though they were shipped the 1,500 miles from the 
panel manufacturer to the building site. 


WIEBOLDT’S DEPARTMENT STORE, Chicago, Ill. 


ARCHITECT: Barancik, Conti and Associates, Chicago, III. 
ENGINEER: David B. Cheskin, Chicago, III. 
CONTRACTOR: B-W Construction Co., Chicago, III. 
PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah 


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heesing a evsntoim wall 


Walls constitute a major consideration in the 
overall design of any building. In high-rise 
structures, they are of paramount importance 
among the several building components. Cur- 
tain walls have gained considerable acceptance 
in recent years as the best method of supplying 
protection and beauty to buildings that rely on 
a frame for structural support. 

Some of the factors that determine the selec- 
tion of a curtain wall material are such esthetic 
considerations as colors, textures, patterns and 
panel shapes and such practicalities as cost, 
availability, handling and attachment, insula- 
tion, maintenance, and fire resistance. Let us 
examine the record of concrete curtain walls in 
the light of these considerations. 


COLORS 


In concrete curtain walls, architects are of- 
fered the widest choice of colors available in 
this field. Solid colors can be chosen from any 
portion of the spectrum—there are no charts of 
predetermined colors to limit the architect’s 
imagination when he works with concrete. 

But solids are only a small part of the color 
story in concrete curtain walls. Mixtures of 
aggregates of different colors and the influence 
of the matrix color give to an architect a peer- 
less control of the coloristic effect for which he 
is working. With the calculation of the psycho- 
logical impact of colors on humans now more 
of a science than an art, it is only reasonable 
that architects work within a medium capable 
of the nuances achieved by the science. 

Aggregates used in the decorative facings for 
concrete curtain walls have ranged from clam- 
shells to ball bearings for unusual applications. 
Those most frequently encountered, however, 
are of quartz, marble, granite, gravel, ceramic 
tile and various ceramic and vitreous materials. 

Quartz aggregates are generally available in 
three varieties—clear, white, and rose (a light 
pink). Clear quartz is widely used since it adds 
a sparkling surface to panels that depend main- 
ly upon their matrix for color. Therefore, it is 
adaptable to use with any color panel. It may 
also be used in combination with colored aggre- 
gates to emphasize the matrix. White quartz 
ranges from a translucent white, verging on the 
clear type, to a deep milky white widely used 
for curtain wall panels. Rose quartz aggregates 
produce concrete ranging from a delicate pink 
to a warm, aged-looking rose color. 

Marble offers architects the widest selection 
of colors among the natural aggregates, namely, 
green, yellow, red, pink, blue, grey, white and 
black. In most areas, blue and yellow marble 
aggregates are available in pastel hues and the 
other colors in many shades running from light 
to moderately dark. 

Granite, long known for its durability and 
beauty, is available in shades of pink, grey, 
black and white. It is usually composed of 30 
per cent quartz and 70 per cent feldspars. 

In certain sections of the country, a pleasing 
brown or reddish-brown gravel is available. In 
these areas it has been used to produce attrac- 
tive, low-cost wall panels. 

A number of manufactured aggregates are 
available in the United States. These extend 
the range of colors in concrete curtain walls into 
the vibrant, bright shades that prove valuable 
for architectural accents. A comparison of typi- 
cal colors of natural and manufactured aggre- 
gates can be made by contrasting Figs. 1 and 2. 
The latter are generally custom manufactured 
to match samples submitted by the architect. 


Fig. 1. A mixture of marble aggregates in several colors 
produced this panel surface. 


Fig. 2. Vitreous aggregates in several bright colors created 
this colorful design. 


iby 


In this category are such aggregates as those 
made of vitreous and ceramic materials and 
ceramic tile. 

Ceramic facing tiles are available in a dazzl- 
ing array of colors and patterns. The tiles, 
inlaid in neat, regular rows, constitute up to 
90 per cent of the panel’s exposed surface. 
Tiles can be obtained in a wide variety of sizes 
but 1-in. square and 1x1 14-in. tiles are common. 

Ceramic aggregates lend drama to panels 
through the richness and luster of their coloring 
and surface. In common with all the manu- 
factured aggregates, it is possible to get prac- 
tically any color when using a ceramic material. 

Vitreous aggregates and tiles provide the 
most intense colors of the materials commonly 
used for decorative concrete curtain wall panels. 
They are often used for murals, signs, and other 
applications requiring eye-catching beauty. 

The matrix has an important bearing on the 
overall color of the panel. Curtain wall panels 
can be made that depend mainly upon the 
matrix to achieve the desired color. Trans- 
parent quartz aggregate is used to heighten the 
luster and coloring of the panel as well as to 
add a durable surface. 

In panels made with colored aggregates, the 
matrix color can either subtly mute or clarify 
the color. White portland cement is usually 
used in the facing mix to ensure utmost purity 
of color, even in many of the darker shades. 

Coloring of the matrix is accomplished 
through the use of mineral oxide pigments. 
Practically all colors can be obtained in this 
manner, including light to dark shades of red, 
green, yellow and brown. 

Intermediate shades of both achromatic and 
chromatic colors are cast by manipulation of 
the matrix and aggregate colors. Many unusual 
pepper-and-salt and similar effects can be 
obtained by mixing multicolored aggregates of 
fairly large size in a white portland cement 
matrix to eliminate visual merging of the 
colors. In addition to these mosaic-like panels, 
it is possible to achieve luminous colors with 
fascinating color-on-color effects that add in- 
terest and character to otherwise unornamented 
walls. 

Concrete curtain walls can be created in a 
virtually unlimited range of colors. Not only 
are the primary colors readily obtainable, but 
through juxtaposition of mixed aggregates in 
colored matrices, it is possible to produce a 
multitude of mutable hues. 


TEXTURES 


Closely allied with color and materially af- 
fecting it is the consideration of surface tex- 
tures. Naturally, a matte finish will alter the 
apparent color of a panel when compared with 


18 


Fig. 3. A surface texture exposing 1/, to ¥-in. aggregates 
was achieved by the aggregate-transfer method. 


Fig. 4. This exposed aggregate surface was ground to a 
smooth finish. 


one finished smooth. Texture also helps de- 
termine the relative visual importance of a 
wall; for example, moderately rough finishes 
usually are less obtrusive than shiny surfaces. 
The textures of concrete curtain wall panels 
range from a glossy, ceramic-like finish to rug- 
ged textures of bold outlines. 

An exposed aggregate panel commonly used 
for curtain walls has an aggregate reveal of ap- 
proximately 1x in. Reveal is largely determined 
by aggregate size; the greater the maximum ag- 
gregate size, the deeper will be the reveal. It 
can be varied by several casting techniques. A 
retarder can be used on the forms as the panels 
are cast face down. The surface mortar is later 
brushed to expose the aggregate more fully. A 
shallow layer of sand is sometimes placed in the 
bottom of the form to cover partially the deco- 
rative aggregate which increases reveal. Figs. 1 
through 4 are close-ups of exposed aggregate 
panels. Aggregates 2 in. to 3 in. in diameter 
were used for the bold texture on the panels 
illustrated in Fig. 6. 

The question of propinquity of traffic flow to 
curtain walls has an important bearing on the 
extent of aggregate reveal desired. When pan- 
els are to be viewed relatively close, such as 
those bordering walkways, less reveal is needed. 
When panels are to be some distance from the 


main flow of pedestrian traffic, greater reveal - 


will be needed for a rough-textured look. 

Exposed aggregate panels ground smooth 
take on a terrazzo-like appearance. Such panels 
have an attractive sheen that enhances many 
colors. Polished panels of pastel colors tend to 
appear white when viewed from afar due to the 
high reflectance of the surface. Therefore, this 
type of surface is recommended for panels situ- 
ated relatively close to the traffic flow or for 
those of medium or dark shades. 

Ultrasmooth or lightly textured panels can 
be cast through the use of plastic form liners. 
These form liners are made from a _ plastic 
sheeting which is glossy on one side and which 
has an embossed leather design on the reverse 
side. When the concrete is cast against the 
smooth side, the color takes on new depth and 
dimension. Examples of panels cast with plastic 
form liners are shown in Figs. 5 and 18. 

Carpet-like textures of various patterns are 
possible with panels cast against rubber form 
liners. Fig. 7 illustrates a common design ob- 
tained with rubber form liners. 

The foregoing textures are only a few of 
those that are commonly encountered in con- 
crete curtain walls.* A wealth of additional 


*A dditional information on concrete surface tex- 
tures is available in the United States and Canada 
from the Portland Cement Association, 33 West 
Grand Ave., Chicago 10, Ill. 


Fig. 5. Integral colors take on a new depth and richness 
when panels are cast against plastic form liners. 


Fig. 6. Large concrete panels for the Grand Super Market, 
Riverside, Calif., were cast at the job site and lifted into 


place. A rough texture was achieved by exposing large 
aggregates in the panel surface. 


19 


textures are available. For example, some of 
those obtainable through the use of form liners 
include the surface textures of concrete cast 
against striated plywood, roughly sawn boards, 
sand-blasted plywood and the screen side of 
masonite. Panels can also be textured after 
curing by mechanical means such as _ bush- 
hammering, tooling or sandblasting as shown in 
Fig. 9: 

In the matter of textures, concrete curtain 
walls open to architects the widest range and 
greatest opportunities for personal expression 
of any currently available material. 


PATTERNS 


Because of the protean nature of plastic con- 
crete, it is admirably suited to patterning. The 
following three basic approaches are most often 
used to create designs in concrete curtain wall 
panels: (1) high and low relief, (2) colored 
aggregates, and (3) contrasting textures. 

Relief designs of practically any form can be 
achieved with concrete panels. Both straight- 
line geometric patterns and free-form shapes 
of unlimited numbers are possible. 

Straightline figures are most often realized by 
the use of negative patterns made of wooden 
strips or metal molds in the forms. Concrete 
can be cast directly on the patterns or deco- 
rative aggregates can be spread on the forms 
and concrete cast afterward to produce a 
relief design with an exposed aggregate surface. 
An alternate method uses a concrete mix with 
white portland cement paste and decorative 
aggregates for the facing backed up by several 
inches of lightweight concrete. 

Several methods of casting free-form pat- 
terns in concrete curtain wall panels are cur- 
rently being used. The techniques used for 
making straightline patterned panels can also 
be used for free-form decorations. Plaster waste 
molds often prove to be most practical when 
intricate shapes are to be formed. If added 
emphasis is desired for certain portions of a 
relief pattern, aggregates of a color that con- 
trasts with the background can be applied to 
the desired portions of the design. 

Plastic form liners offer the means of obtain- 
ing both straightline and free-form patterns on 
concrete wall panels. After a design has been 
decided upon, a wooden or plaster negative 
pattern mold is made. With the mold and the 
usual vacuum forming technique, it is possible 
to make any number of form liners of the 
thermoplastic material used in this work. 

Virtually any design can be achieved in 
plastic form liner work as long as the following 
three rules are observed: (1) Limit depth of 
design to 1% in. to 1 in. in most cases. (2) 
Maintain a 10-deg. draft on all indentation 


20 


Fig. 7. This precast panel is one of many used to enclose 
a parking garage in Athens, Ga. The textured surface was 
made by casting concrete against a rubber matting form 
liner. Architect: Heery & Heery; contractor: C. C. Robert- 
son, both of Athens. 


Fig. 8. A rough texture created by casting plain concrete 
against alternating panels of sandblasted form boards. 


sides. (3) Keep all edges and corners rounded. 
Relief may be more than 1 in. if the depressed 
area is sufficiently wide. 

There are several methods by which designs 
can be obtained through the use of colored 
aggregates. One technique commonly em- 
ployed outlines the desired pattern with nar- 
row wood or metal strips. The predetermined 
colored aggregates are placed in the appro- 
priate outlined sections, the strips are removed 
and white portland cement concrete is cast 
atop the decorative aggregates. When backed 
up with a grey concrete mix, the result is a 
strikingly attractive curtain wall panel. 

Another means of producing colored aggre- 
gate designs is the aggregate-transfer tech- 
nique. In this method, colored aggregates are 
placed on a plywood form liner coated with 
adhesive. After the adhesive has hardened, 
concrete is cast against the liners and cured. 
Since the bond of the aggregate is greater to 
the concrete than to the adhesive, the aggre- 
gate is “‘transferred”’ to the surface of the con- 
crete when the liner is stripped.* 

The profusion of decorative aggregates of 
varied colors and textures enables architects 
to achieve unique architectural effects through 
patterns using several types of natural and/or 
manufactured aggregates. Full-color designs 
can be anything from a simple circle or dia- 
mond pattern (Fig. 10) to elaborate designs 
(age ul) 

Innumerable patterns are possible through 
the manipulation of concrete surface textures. 
A few of the textures available were mentioned 
in an earlier section. The opportunity for de- 
signs through texture is obvious to any archi- 
tect. Rough form boards can be laid in a ran- 
dom pattern. Rubber form liners might be cut 
into squares and set with their linear texture 
running at 90-deg. angles to contiguous squares. 
Panels cast against the textured side of plastic 
form liners can be arranged in leather-like 
square patterns. The possibilities are unlimited. 

And “‘unlimited”’ is an apt word to describe 
the entire gamut of pattern possibilities open to 
architects specifying concrete curtain walls. 
In no other medium is it possible to enjoy the 
freedom of design through the multiplicity of 
controlled effects—relief, color and texture. 


PANEL SHAPES 


Concrete panel shapes have ranged from the 
ubiquitous rectangular panel to square, dia- 
mond, curved and multiplanar panels. Unusu- 


*Additional information on the aggregate- 
transfer method is available in the United States 
and Canada from the Portland Cement Association, 
33 West Grand Ave., Chicago 10, Ill. 


Fig. 9. Concrete surface textured by bushhammering after 
removal of forms. 


Fig. 10. Color and pattern in these wall panels were 
achieved by a colored concrete matrix and clear quartz ag- 
gregate with the columns accented by covers of thin red 
panels. 


ally shaped panels are much easier to manufac- 
ture in concrete than in other materials due to 
the plasticity of concrete as it is being cast. A 
pleasant departure from severe rectangular 
building shapes is shown in Fig. 12 which 
shows exposed aggregate panels that are sculp- 
tured to the curving lines of a library bay. L- 
shaped panels, such as those in Fig. 13, reflect 
the patterns set up by the sunshades and re- 
sultant shadows that are an integral part of the 
facade of this building. Panels thickened at 
midsection alternated with flat panels and 
windows result in an attractive three-dimen- 
sional wall with a checkerboard pattern on the 
office building pictured on page 13. Fig. 14 
depicts the striking decorative effect obtained 
by erecting square panels diagonally. 

Precast concrete curtain wall grilles have 
won considerable popularity because they com- 
bine beauty and practicality. Two types are 
commonly encountered—punctured concrete 
panels, such as those shown in Figs. 15 and 16, 
and relatively small units erected much the 
same as concrete masonry (see Fig. 17). 

Concrete curtain wall panels can be cast with 
a grillework over all or part of the surface to 
achieve a delicate filigree beauty. Panels are 
most often used when the grillework is not to 
cover an entire wall of a building. For more 
extensive areas, masonry units especially cast 
to create the desired pattern are eminently 
satisfactory. One of the three following face 
sizes is usually specified for these units since 
they conform to the mold boxes of standard 
block machines: 8x8 in., 12x12 in., or 8x16 in. 
A stacked bond is most often used in this work 
since it maintains the geometry of patterns 
and produces unbroken edges at wall openings. 

Thus, in all the design variables—colors, 
textures, patterns and panel shapes—curtain 
walls of concrete prove to be the most versatile 
available for this work. 


COST 


An artist must work within the restrictions 
imposed by his art and himself. Architects, 
too, cannot be swayed solely by the design pos- 
sibilities offered with the use of a material. 
They must also consider such practicalities 
as cost, availability, handling and attachment, 
insulation, maintenance, and fire resistance. 
Fortunately, in terms of practicalities, as 
well as esthetics, concrete curtain walls have 
the scales tipped heavily in their favor. 

Attention has been called several times to 
the value of concrete’s plasticity and sculptural 
qualities in broadening design possibilities. 
These characteristics also simplify the manu- 
facture of precast wall panels, thereby lowering 
their cost considerably. Unusually shaped con- 


22 


sant sae annatememonmmanninaiattas 


Fig. 11. This stylized fish illustrates the free-form de- 
signs that can be achieved in exposed aggregate panels. 


Fig. 12. Curved concrete panels enclose the reading room 
portion of the City Library in Charlotte, N. C. An attrac- 
tive exposed aggregate surface was specified by the architect, 
A. G. Odell, Jr., and Associates. The panels were made 
by Concrete Materials, Inc., for the general contractor, 
J. A. Jones Construction Co. All are located in Charlotte. 


crete panels are not materially more expensive 
than conventional rectangular ones. Even 
elaborate surface designs, such as those shown 
in Fig. 18, can be economically realized by 
several techniques. 

In this country, the labor required to cast 
panels has a considerable bearing on ultimate 
cost. Unornamented concrete panels made 
with gravel and sand aggregates can compete 
successfully with the cheapest type of walling. 
As ornamentation becomes more extensive and 
intricate and as the panel cross-section grows 
more complex, the cost will naturally increase. 
However, a comparison with comparable com- 
peting curtain wall panels (if they are capable 
of the effects and uses of the concrete panels) 
will underline the economy of concrete. 

In many cases concrete wall panels can be 
furnished that constitute the entire wall. This 
eliminates the need for expensive finishing of 
the interior wall surface. It also results in a 
wall of reduced cross-section when compared 
with competing panels with their backup and 
interior finish. Once the concrete wall panel 
has been erected, the wall is completed. 

The materials for concrete wall panels are 
low in cost. The use of white portland cement 
in the matrix will enhance the clarity of colors 
obtained. Coloring the matrix will vary in 
price in proportion to the cost of the mineral 
oxide pigment and the depth of color desired. 
Shades of red, orange, yellow, brown, black 
and grey are especially inexpensive because 
these pigments are low priced and it takes a 
relatively small amount of pigment to color 
the matrix. Brilliant, deep yellows are usually 
difficult to obtain because suitable mineral 
oxides are not readily available. Deep shades 
of blue and green are ordinarily more expen- 
sive; but, since the facing mix is only 1 in. in 
depth, the cost of coloring the matrix is a rela- 
tively minor consideration. 

Decorative aggregates vary in price in re- 
lation to the availability of natural aggregates 
and to the total cost of making manufactured 
varieties. Transportation also figures largely 
in the cost of decorative aggregates. Marble 
aggregates are generally available throughout 
the United States and are low in cost for most 
types. Quartz and granite are slightly higher 
in price than marble since their high density 
makes them more difficult to quarry. Gravel 
naturally is the lowest priced of all aggregates. 
The cost of ceramic materials is from three to 
five times that of marble. Vitreous aggregate, 
supplied uncrushed, costs approximately 10 to 
12 times as much as marble. 

However, even the most expensive aggre- 
gates often are practical because they are used 
only in the 1-in. facing layer. If the aggregate- 


Fig. 13. L-shaped panels with two colors of exposed ag- 
gregate were effectively used with L-shaped canopies accent- 
ing the pattern. 


Fig. 14. This modern library in Bakersfield, Calif., illus- 
trates the use of square precast exposed aggregate panels 
rotated 45 deg. Small precast units were inserted at panel 
corners. The architect was Whitney Biggar, and the gen- 
eral contractor was Guy Hall, both of Bakersfield. Panels 
were made by the C. D. Wailes Co. of Los Angeles. 


23 


transfer technique is employed, which applies 
a single layer of decorative aggregate on the 
surface of the panel, costs are accordingly 
lowered. 

Another factor in cost determination is cast- 
ing technique. As has been noted, aggregate 
transfer is especially economical when expen- 
sive decorative aggregates are used. The choice 
of casting procedure will be dictated largely by 
the physical and economic requirements of the 
project in question. Also, the matters of at- 
tachment and jointing details have an im- 
portant bearing on costs. 

Architects should consult a producer of pre- 
cast concrete wall panels before plans are pre- 
pared. He can provide specific information on 
local concrete curtain wall construction costs 
and practices. 


AVAILABILITY 


Concrete wall panel producers are now lo- 
cated in practically every state, and in most 
well-populated areas there are several panel 
producers. Shipping panels within a 300-mile 
radius is common practice; and panels have 
been transported up to 1,500 miles and re- 
mained competitive. On some large projects 
and those where transportation is difficult, 
panels can be job-cast with subsequent sav- 
ings. In the majority of cases, however, panels 
manufactured in well-established plants prove 
most satisfactory since the greatest amount of 
control and flexibility can be exercised under 
such conditions. 


HANDLING AND ATTACHMENT 


Handling and attachment practices followed 
with concrete wall panels have been perfected 
in the many years they have been in use. Ship- 
ment is ordinarily via trucks. Panels vary 
greatly in size and shape, but the 8x14-ft. 
rectangular panel is commonly specified since 
it is large enough to be economical in erection 
time and yet not too large for ease of transpor- 
tation and handling. Panels cast at or near the 
job site can be larger. If panels must be trans- 
ported for considerable distances, the pro- 
ducers must check such contingencies as heights 
of underpasses and highway load limitations. 
In most cases, contracts for supplying curtain 
wall panels include fabrication, transportation 
and stockpiling at the job site. This practice 
relieves the architect of such burdensome 
details. 

Panels are often lifted directly from the truck 
into final position on the building. Lifting 
can be done by strap slings or by inserts cast 
in the back or edges of the panels. These in- 
serts can also double as fastening devices. 
Panels can be supported by integrally cast 


24 


Fig. 15. Precast grilles with exposed quartz aggregate sur- 
face conceal window areas in the Mormon Temple, Los 
Angeles, Calif. Architect: Edward G. Anderson. General 
contractor: Jacobsen Construction Co. Panel fabricator: 
Buehner Co. All are located in Salt Lake City, Utah. 


| J 
f = 


2 
f = 


1, Fel 
LC ethene 


ee 
7, Fel 


— em 


Fig. 16. An ancient Mayan motif is the basis of design 
for this intricate grille in white exposed quartz aggregate. 


lugs, which eliminate expensive steel shelf 
angles. Many types of fastening details are 
available to accommodate all the possible 
combinations of panels and building frames. 
A few of these details are described in ‘“‘A Few 
Attachment Details’? beginning on page 28. 


INSULATION 


The swift acceptance and wide application 
of air conditioning have greatly increased the 
importance of the insulating value of walls. 
Heating and ventilation engineers estimate that 
it costs up to three times more to cool than to 
heat a given quantity of air. Consequently, 
insulation is an important factor in curtain 
wall construction in all areas of the country. 

Lightweight aggregate concrete used as struc- 
tural backing for curtain wall panels often pro- 
vides sufficient insulation without need for 
additional materials. A panel composed of 5 in. 
of expanded shale aggregate concrete and a 
decorative surface of 1 in. of quartz aggregate 
concrete has a ‘“U”’ value of approximately 
0.34. Additional insulation may be secured by 
plastering the inner panel surface with vermi- 
culite or perlite plaster. Panels 4 in. thick with 
an exposed aggregate facing backed with per- 
lite concrete have a “‘U”’ value of about 0.15. 

Another type with a low ‘‘U”’ value is the 
sandwich panel. These units are composed of 
two thin layers of concrete enclosing a layer 
of insulating material such as cellular glass, 
fibrous glass or foamed polystyrene. The total 
thickness of these panels ranges from 5 to 8 in., 
depending on insulating and structural require- 
ments. These panels are finished attractively 
on both faces so that they constitute the entire 
wall. No further work on the wall is required 
once they have been fastened in place. 

The effective insulation provided by this 
type of panel is shown by the ‘‘U” values 
achieved in sandwich units 6 in. thick with a 
1-in. core of various insulating materials. These 
values range from 0.16 to 0.21 depending on 
the type of insulating materials used. 

Concrete curtain wall panels are secured to 
building frames in a manner that requires no 
connectors or metal mullions to extend through 
the wall. This prevents a path of heat and cold 
transmission from existing between the exterior 
and interior of the building. Prevention of this 
adverse effect is one of the reasons why a build- 
ing clad with concrete panels is more economi- 
cal to heat and cool. 


MAINTENANCE 


Imagine subjecting a construction material 
to 145 freeze-thaw cycles per year, submerg- 
ence in sea water twice daily, and exposure to 
the wind and other rigors of a Maine seacoast. 


<3 


Te aT 


Ps. ad 

ett 
a ee er 

ENN 


x 
My 
Dy 


iF 
€ 


Ay 
Leann 
MLL 


Fig. 17. Precast concrete grille units were set up much as 
is concrete masonry to create the striking curtain walls for 
these college dormitories. 


25 


It is under such conditions that a number of 
precast concrete specimens are undergoing a 
test at Treat Island, Maine. After five years of 
exposure (663 freeze-thaw cycles) there was 
still no sign of deterioration of practically all 
of the air-entrained concrete specimens. Such 
resistance to the effects of weathering dramat- 
ically illustrates the durability and low mainte- 
nance needs of concrete wall panels. 

Since most of the surface area of an exposed 
aggregate panel is composed of the rugged 
aggregate and because matrices in these panels 
usually test over 6,000 psi, concrete panels are 
both long-lasting and fadeproof. Quartz aggre- 
gate has a hardness rating of 7.0 on Moh’s 
scale, approximately that of carbon steel. 
Granite, composed of 30 per cent quartz and 
70 per cent feldspars, has a rating nearly as 
high as quartz. Gravel and marble vary in 
hardness from 3.0 to 7.0 on Moh’s scale. Vitre- 
ous aggregates are rated at approximately 5.5. 
No tests have been conducted on ceramic 
aggregates but it is believed that their hard- 
ness would be about that of high-grade marble. 
Thus, it is apparent that decorative aggregates 
have an expected span of usability ranging 
from 50 to over 200 years! 

Moisture absorption rates for quartz, granite, 
marble and gravel vary from 0.05 to 0.50 per 
cent—a completely negligible amount. Mois- 
ture absorption rates of vitreous aggregates are 
too low to measure accurately. The moisture 
absorption qualities of ceramic aggregates are 
related to their chemical composition and 
length of burning. Since an extremely dense 
cement paste is used, moisture absorption over 
the entire panel is kept to a very low figure. 

Because thermal volume changes in concrete 
panels are exceptionally small, movement at 
joints is kept to a minimum. When a sealant 
containing Thiokol liquid polymers is used, an 
ideal maintenance-free joint is achieved. Once 
a concrete curtain wall has been erected, archi- 
tect and owner can be sure that the long-range 
cost picture will be as pleasant as the im- 
mediate one. 


FIRE RESISTANCE 


The excellent fire-resistive qualities of con- 
ventional concrete construction have long been 
recognized. These same qualities apply to con- 
crete curtain walls. Concrete wall panels are 
not only noncombustible, but they also act as 
effective fire barriers. Such panels can be pro- 
vided in the thicknesses and varieties of con- 
crete that will conform to any building code 
requirement—including the maximum fire rat- 
ing of four hours. 


26 


Fig. 18. The versatility of concrete may be seen in these 
glossy panels cast in plastic form liners. Variety of pat- 
tern and color is unlimited. 


Fig. 19. Towson Plaza, Towson, Md., a shopping center 
of 40 stores, owes much of its beauty to precast wall panels 
made with a quartz aggregate and white cement. Archi- 
tect-Engineer: Leavitt Associates, Norfolk, Va. Consult- 
ing Architect: Lathrop Douglass, New York, N.Y. Owner- 
Contractor: Towson Plaza, Inc.; Sanzo & De Chiaro, 
Baltimore, Md. Panel Producer: Standard Prestressed 
Concrete Corp., White Marsh, Md. 


As this study of the crucial considerations 
in determining a suitable curtain wall material 
has unfolded, it has become increasingly ap- 
parent that concrete offers advantages of great 
importance to all concerned—architect, owner, 
engineer and contractor. Only concrete curtain 
walls combine such imposing assets in both 
esthetics and practicalities. 

The need for compromise has been eliminated. 


First National Bank Building, Denver, Colo. 


28 


There are many types of fastening or attach- 
ment devices used successfully for holding pre- 
cast wall panels to building frames. The size of 
the panels, type of building frame and proposed 
appearance of the facade will influence the 
choice of fastening methods. Usually, the archi- 
tect devises a system of attachment that will 
meet the demands of the design, both struc- 
turally and architecturally, and comply with 
local building codes. Following or during the 
development of fastening methods, consulta- 
tion with a panel fabricator may indicate some 
changes to facilitate casting, handling and ship- 
ping operations and to simplify attachment to 
the building. 

In one simple method, clip angles are cast in 
or welded to columns, intermediate struts, or 
beams, and panels are bolted or welded to the 
clip angles. Another method provides for sup- 
porting panels on angles that have been cast in 
or welded to the building frame. Inserts are 
welded to panel reinforcing to ensure a perma- 
nent connection. The number and location of 
inserts will depend on panel size and location 
of the column or other support. 

Attachment methods used on a number of 
buildings are shown in Figs. 20-26. 


In the 3660 Grand Apartments, Des Moines, 
Iowa, the precast panels were supported at 
floor level by angles and bolted to steel straps 
previously welded to the columns. Bolts were 
cast in the backs of panels at locations to meet 
the steel straps. This arrangement anticipated 
a moderate amount of adjustment to meet any 
building variations. The system proved quite 
satisfactory because it made it possible to place 
panels for each floor in less than an eight-hour 
shift. The vertical joints between the panels 
were filled with a weather-stripping material 
and calked. 


Fig. 21. 


Panels for the Maule Industries Office Build- 
ing, Miami, Fla., were cast with inserts in the 
back of the units similar to those used in tilt-up 
panels. Bolts were cast in the building frame 
at the floor line and spandrel beam. A 4-ft. 
long, 4x4-in. angle with slotted holes was used 
as the connecting member between panel and 
anchor bolts. The slotted holes provided suf- 
ficient leeway for panels to be lined up properly 
with adjacent units. A high-grade calking 
material was used to seal the offset type of 
joints between panels. The system used was a 
simple and easy way to secure the wall panels 
to a building frame of this type. 


3x 3'x z clip angle welded to 
= 3x 4"sq, plate 


14'-O' typical 


L joint with 

weatherstripping 
Precast exposed- 
aggregate panel 


Cast-in-place 
column 


14-0" typical 


Precast exposed- Column 


aggregate panel 


I" rigid 
insulation 

a 25x25x3L4' Ig. 
eek oh Ae welded to floor 
3'x3'x2 L6"Ig. 


Castin-place 
floor joists 


14'-O" first story 


SECTION 


Concrete spandrel 
Suspended ceiling 


DETAIL A 


Metal insert 


4x 4x2L4"g. 


DETAIL B 


Calking 
compound 


29 


The connection details at right are for the 
panels on Wieboldt’s Department Store in 
Chicago. Each bay of the building elevation 
requires nine 8x14-ft. panels—three horizon- 
tally and three vertically with the long panel 
dimension vertical. Bolts for clip angles were 
cast in the exterior building columns, and two 
tee studs were erected between floor and 
ceiling at the third points between columns. 
Inserts welded to the panel reinforcement were 
cast in the panels. The panels were erected by 
bolting to the columns, tee studs and short 
angle sections in the edge of the floor. After 
panels were aligned and in final position, the 
connections were welded. Premolded joint fill- 
er material was secured to the panel edges just 
before erection. Later, all joints were calked, 
front and back, with elastic calking material. 
The attachment system provides adequate 
support, rapid erection and simple fixtures. 


Fig. 23. 


ae sa A>. SA DY 
The L-shaped panels enclosing the Fremont 
Hotel in Las Vegas, had angles welded to the 
panel reinforcement and extending out the 
back. These were horizontal and were located 
just below level of the floor surface. Slots in 
the angles fitted over anchor bolts recessed in 
the floor. Six-inch tee struts between floor 
and ceiling were located behind vertical panel 
joints. Two small metal inserts cast in the 
panel back near each end were welded to the 
tee strut after final alignment of each panel. 
An offset type of joint was cast in the panel 
edges to provide a tight seal after calking. This 
method of attachment ensured stability of the 
unusual panel shapes. 


30 


Precast column facing 


oe. 


Precast exposed 
aggregate panel 


Connections welded 


after panels are in AA| 


Premolded /4x4 T- column 
fa bent plate 4"x6'clip 
fe angle 


Precast column 


Precast exposed aggregate panel ¢ | 
facing, 2-in. thick 


TYPICAL PLAN 


Exposed aggregate panel 


SECTION A-A 


to reinforcement 
in precast panel 


Fig. 24. 


/Prismatic-shaped panel 


rRemovable lift hook 


In the design of the Wachovia Bank & Trust 
Co. Building in Charlotte, N.C., prismatic- 
shaped panels were developed and detailed to 
fit between the windows. The units were sup- 
ported by lugs to the building frame and aligned 
by a series of 5-in. vertical channels. Remov- 
able hooks that screwed into inserts cast in one 
end of the panel were used to lift each unit into 
place on the building. Joints between panels 
were closed with a premolded cross-shaped 
gasket material and a Thiokol-base calking 
compound. Simple fastening fixtures permitted 
panels to be lifted directly from the delivery 
truck into final position. 


Fig. 25. 


Precast coping 


_— V-shape joint 
ee 


Angle to attach 
ah anel bolts 


PSs 
iy 


Seat angle welded 
to column to support 


Rectangular panels on McGuire Hall Annex 
of the University of Virginia Medical Center in 
Richmond have an integral canopy. To support 
these large panels and secure the canopy units, 
a simple but effective attachment system was 
devised. Angles were welded to the columns 
and the panels seated on these members. 
Other angles were welded to building beams at 
a point below the top edge of the panel. Bolts 
cast in the panel back fitted into slots in these 
angles to hold the panels securely on the build- 
ing. V-shaped joints were cast in the panel 
edges to provide a tongue-and-groove fit be- 
tween units. A dry calking material was first 
forced into all joints and then sealed with an 
elastic calking compound. 


Metal flashing 
with drip 


Flat bar to 
attach panels 


Window sill 


| 


The panel attachment detail used for the 
Nurses’ Building of St. Mary’s Hospital in 
Knoxville, Tenn., is simple but ingenious. 
Concrete canopies at each floor were cast in 
place at the time the floor was cast. A metal 
channel track was welded to a floor plate cast 
in the concrete along the centerline of the ex- 
terior wall. Directly above this, two angles 
were secured to the ceiling parallel to but 
separated by the width of the precast panel. 
Small steel plates were cast in the bottom edge 
of the exposed aggregate sandwich panels to 
act as runners or shoes. Panels were then slid 
into position from one end of the building, a 
method that proved to be fast and simple. The 
bottoms of the units were grouted into place 


canopy 


angle covers 


Cross-shaped premolded 


rubber joint Precast 


sandwich panel 


Metal 
flashing 


Plate cast in panel 


SD Channel track welded to 
on floor plate 


and metal flashing installed. The overhead 
angles were concealed with aluminum covers. 


Fig. 27. A detail commonly used for supporting thin facing panels is shown below. Lugs or supporting haunches, in- 
tegrally cast in the back of the panel, bear on the floor slab. Such lugs are easy to cast and usually lower erection costs. - 


oe nachore in bocke aa 


Concrete masonry 
Plaster 


+ 


ee haunches 
ee 


aad 


Support haunch 


Stiff mortar 
Oe Sey ee 
on 


6" 


SECTION 


SECTION A-A 


ay ELEVATION 


PORTLAND CEMENT ASSOCIATION, 33 West Grand Avenue, Chicago 10, Wlinois 


‘The activities of the Portland Cement Association, a national organization, are 
limited to scientific research, the development of new or improved products and 
methods, technical service, promotion and educational effort (including safety 
work), and. are primarily. designed to improve and extend the uses of portland 
cement and concrete. The manifold program of the Association and its varied 
services to cement users are made possible by the financial support of over 70 
member companies in the United States'and Canada, engaged in the manufacture 
and sale of a very large proportion of all portland cement used in these two countries, 
A current list of member companies will be furnished on request. 


...@ modern method of 


building with reinforced concrete 


PORTLAND CEMENT ASSOCIATION 33 w. GRAND AVE., CHICAGO, ILL. 


What [0 Vile-Up? 


ILT-UP construction is a special form of precast concrete construction. As used in this 
Races. it is limited to construction in which the walls are cast on the site in a horizontal 
position, tilted to the vertical position, set in place and made an integral part of the completed 
structure. There are a great many different ways of designing and erecting such structures, par- 
ticularly as to the details. Each designer and builder has his own methods and details which 
he is constantly trying to improve. It is the purpose of this booklet to show some of the prac- 
tices which have proved satisfactory and to point out some to be avoided. The methods and 
details shown should not be considered as the only satisfactory. ones but they will be helpful 
in developing details and procedures most suitable for a specific job and for the personnel and 
equipment available. It will be advantageous for the designer to consult with possible contrac- 
tors before the design and construction details are definitely established. He should at least 
consider the personnel and equipment available in the area. Even small changes in design or 
construction procedure may result in appreciable saving in time and money as well as pro- 


viding a better structure. 


Front Cover— 
A small industrial crane is tilting these 12-ft. high 
thick panels. A 6x6 angle distributes the lifting fc 
along the top edge of the 18-ft. wide panel. 
panel in the foreground, a yoke of 2x6 and 2x 
has been used to stiffen the 2x6 edge forms. 


HISTORY 


ILT-UP construction is generally considered as a new 

development because most of the buildings erected 
by this method have been built since about 1946. Ac- 
tually, the method was used prior to 1912 and for a few 
housing developments and buildings of various other 
occupancies built between 1912 and 1946. 

Most buildings constructed by the tilt-up method are 
one story in height, although there are some up to eight 
stories. Generally the multistory buildings have been con- 
structed by tilting the walls for one story, placing the 
floor above, and then repeating the process. In some in- 
stances walls two stories in height have been cast and 


tilted as a unit. In fact, one of the earliest examples of 
tilt-up construction had the two-story walls cast on a 
platform which was tilted with the wall. 

Various schemes have been tried using tilting plat- 
forms but by far the most common method is to cast the 
wall panels on the concrete floor, using the floor as the 
bottom form, and then tilt them into position. 

Improvised hand equipment was used for tilting early 
jobs. At the present time most of the tilting is done with 
various types and capacities of power equipment ranging 
up to specially built machines capable of handling loads 
of 50 tons. 


Copyright, 1952, by Portland Cement Association 


This building, photographed in 1947, was 
built by the tilt-up method at Des Moines, 
lowa, between 1906 and 1912. Below is 
shown the front being tilted. The platform 
on which this wall was cast was tilted with 
the wall. Some of the walls are hollow, made 
by casting a 2-in. layer of concrete, placing 
a 2-in. layer of sand and then casting the 
top 2-in. layer of concrete. The two layers 
of concrete are tied together with reinforce- 
ment. The sand was washed out with a fire 
hose as the wall was tilted. 


In 1912 several buildings were erected of 
tilt-up construction for the Army at Ft. Crock- 
ett, Galveston, Texas. This is one of the 
houses photographed in 1951. Willard E. 
Simpson, architect. 


fl areas is adaptable to a wide range of uses and archi- 
tectural effects. It has been used for many types of 
structures from private homes and garages to multistory 
office buildings, although by far its greatest use has been 
for one-story industrial and commercial buildings. 
Construction time is relatively short with this method. 
Time-consuming form construction or setting of thou- 
sands of small units. is avoided. As an example, for a 
45x80-ft. building, a crew of eight inexperienced men 


Owen Building, Columbia, S.C. The 
frame and floors for this building 
were erected in the usual manner 
and then the wall panels cast on the 
floor, and tilted into position. The 
walls are composed of 2 in. of regu- 
lar concrete and 6 in. of vermiculite 
concrete. Lafaye, Lafaye and Fair, 
architects. R. C. Johnson, engineer. 
General Construction Company, con- 
tractor. 


set the forms and cast the panels in one day and erected 
them complete with wall columns in two days. 

In the very important matter of cost, tilt-up construc- 
tion also has advantages. It is always unsatisfactory to 
give general cost figures or comparisons as varied design 
requirements and local conditions influence cost on each 
job. However, in nearly every instance where competi- 
tive bids have been taken, tilt-up construction has been 
bid lower than any other comparable wall. 


Office building of Southern Express 
Company, Dallas. Herman Cox, 
architect. McFadden and Miller, con- 
tractor. 


4 


This view shows the office 
portion of the Central 
Freight Lines Terminal at 
Fort Worth, Texas, one of 
several tilt-up buildings 
erected for this company. 
W. E. Lessing, architect. 
Joe Caulker, contractor. 


Wall panels must be designed for the conditions to 
which they will be subjected in the completed structure 
and during erection. The general design of the building 
will determine whether the walls are load-bearing or non- 
load-bearing with a continuous footing or supported on 
the column footings only. The design for these conditions 
after the walls are in position will be little if any different 
than for walls of reinforced concrete built in the conven- 
tional manner. The only difference will be in details. 

Sometimes it is economical to consider the wall panels 
as deep beams spanning between the columns. Some 
builders cast panels to extend from pier footings to para- 
pets. In buildings with floors at dock height, the lower 
portions of these panels are designed to retain the com- 
pacted fill on which the floor is placed. 


Lifting Stresses 
Tilting a wall panel creates stresses not encountered 


Wholesale grocery warehouse of 
Hale Halsell Company at Tulsa, 
Okla. David R. Graham, archi- 
tect. Tulsa Rig Reel and Manu- 
facturing Company, contractor. 


5 


in conventional cast-in-place construction and with some 
pickup arrangements an exact analysis may be rather in- 
volved. The method of attaching the lifting equipment 
must be known in order to determine the stresses. If the 
attachment is to a stiff channel or angle bolted to the top 
edge of the panel, the latter will be designed as a simply 
supported slab. 

With a 2-point pickup along the top edge, the maxi- 
mum positive moment in a solid panel will occur along 
a horizontal line at about mid-height of the panel, and 
can be determined with reasonable accuracy by consider- 
ing the panel as a slab simply supported along the top 
and bottom edges. The intensity of this moment will vary 
along the centerline of the panel with the maximum oc- 
curring opposite the pickup points. With the pickup points 
at the quarter points of the top edge, the maximum inten- 
sity of positive moment will be only about 0.15wh? even 
for a panel having a width twice its height. The maximum 


Tilt-up construction can be used successfully in the construc- 
tion of houses with a wide range of architectural styles. 


negative moments occur on lines approximately from the 
pickup points to the nearest lower corners of the panel 
with the maximum intensity near the pickup points. The 
maximum negative moment will be about 0.11wh? for 
a square panel and will increase to about 0.32wh? for a 
panel twice as long as it is high. In these formulas w is 
the weight per square foot of wall and h is the height in 
feet. To reduce this high negative moment in long rec- 
tangular panels, it is obvious that it will be desirable to 
move the pickup points toward the corners. Using more 
than two pickup points will reduce both the maximum 
positive and maximum negative moments. 

It is assumed that a spreader is used on the pickup 
lines so that the lifting force at the pickup points is ver- 
tical. If this is not done the moment between pickup 
points will be greater than indicated above. 

The lifting stresses can be reduced considerably by 
placing the pickup points some distance from the top 
edge. Locating the points one-quarter of the way down 
instead of at the top edge reduces the moments about 60 
per cent. 

Strongbacks have been used very satisfactorily on 
many jobs. However, their benefits are primarily due to 
lowering the position of the top attachment points. At- 
tachment points close to the bottom edge have little effect 
upon the moments. The effect of additional intermediate 
points of attachment will depend upon the relative stiff- 


1 


oe 


Maxcy Gregg Park Bathhouse, Columbia, S.C. 
The canopy is an extension of the reinforced 
concrete roof. The building was designed by 
the city and built by General Construction Co. 


ness of the panel and the strongback. With panel and 
strongback of normal size the panel is so much stiffer 
than the strongback that little load will be carried at in- 
termediate points. In fact, if the lifting equipment is at- 
tached to the strongback an appreciable distance beyond 
the top attachment to the slab, the strongback may de- 
flect enough to press down on the slab rather than lift it 
at the intermediate points. Even an infinitely rigid strong- 
back would have little effect on moments in the longitu- 
dinal direction, which are the important ones in panels 
of greater width than height. 

Strongbacks are advantageous where openings in the 
panel appreciably reduce its strength at critical sections. 

Stiffening members bolted to the sides or to the sides 
and top of a panel will reduce the bending moments 
within the panel for the same pickup points. The amount 
of the reduction will depend upon the stiffness of the 
frame, shape of panel, and location of pickup points. 
With side members only, the vertical positive moments 
will be reduced but there will be little reduction in the 
horizontal moments. Side members will be advantageous 
for relatively high panels where the vertical moments are 


greater than the horizontal moments. With the frame on 
the sides and top, all moments will be reduced as com- 
pared with those occurring in a panel without frame and 
with pickup along the top. Frames are particularly ad- 
vantageous for panels with large openings. 

Openings present an individual design problem for 
each size and location. However, a rule-of-thumb which 
is satisfactory for ordinary conditions is to consider the 
actual weight of the panel as distributed over the total 
area including openings. The steel which would normally 
extend through the openings is concentrated at the sides 
of the openings, both horizontally and vertically. 

Higher unit stresses may be allowed for lifting than 
for other design purposes. Lifting stresses occur only 
during tilting and at no other time. It is therefore con- 
sidered satisfactory practice to use a unit design stress 
approaching the yield point of the reinforcement. Even 
though sufficient steel is provided to prevent failure, it is 
good practice to make sure that the flexural stress in the 
concrete when computed for the transformed section is 
below the modulus of rupture strength (approximately 
O.1f, +200). 


Dobson Elementary School, Lancaster, $.C. was designed and built by T. W. Belk. The section at the entrance was cast in place. 


a ee 


carer na eres 


[fRarvers é , fs 
0 Ren Rr “ae om ‘f 


Tilt-up construction was used for most of the buildings in the 93 
acres of this Los Angeles International Airport Industrial Tract. 
Hayden-Lee Development Company, owner-contractor. $. Charles 


Lee, architect. 


Loads 


The total load to be used in computing erection stresses 
must be assumed. In addition to the dead load of the 
slab, there is some resistance to the initial movement, 
the amount depending on the type of bond prevention 
material, surface condition of the floor, moisture condi- 
tion, lifting speed and possibly other factors. Experience 
indicates that where care is taken to prevent bond be- 
tween the panel and floor, the initial resistance to move- 
ment is only slightly greater than that due to the weight 
of the slab. 

Some contractors use jacks to break the initial bond 
by moving the panels horizontally or by raising them off 


the floor slightly. Jacking not only reduces stresses by 
breaking the bond slowly but also by eliminating the 
whipping or bouncing that sometimes occurs with long 
leads when the panel breaks free from the floor slab. 
Preliminary breaking of the bond also allows the use of 
lighter tilting equipment. Although jacking has some ad- 
vantages and may be desirable on some jobs, it is not 
necessary for most conditions. 

The most common wall thickness is 6 in., nominal or 
actual, because this dimension generally meets structural 
requirements and is such that average-size panels can be 
erected without extreme care. Using the nominal dimen- 
sion results in an appreciable saving because 2x6 dressed 
lumber can be used for the edge forms. 


Warehouse and office of 
Northern Drug Co., Fargo, 
N.D. The panels for the 
first story walls were cast 
and tilted. Then the sec- 
ond floor was cast and 
the procedure repeated. 
Oliver Stoutland, architect. 
Meinecke and Johnson, 
contractors. 


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These three buildings show the use of tilt-up construction 
combined with cast-in-place architectural concrete. The street 
fronts of the buildings are cast in place while the remainder 
of the walls are tilt-up. For the Safeway store at Ft. Worth, 
Texas, the architect was Smith and Warder and the con- 
tractor was Cain and Cain. The office and warehouse of 
Kessler-Simon Machinery Company at Oklahoma City, Okla. 
was designed and built by Boecking Company. The Wilson 
Motor Company salesroom and garage at Columbia, S.C. 
was designed by William Morgan, engineer, and built by 
General Construction Company. 


1. This shows the construction ready for the concrete. The edge 
forms have been placed on the concrete floor slab, bond pre- 
vention material sprayed on the slab, reinforcement placed 
and inserts set. By using short bars for dowels to the columns, 
the reinforcement can be made as a mat on a jig outside the 
forms and placed as a unit. This also reduces scuffing the 
bond prevention material. The blocks under the reinforcement 
are removed as the concrete is placed. Bolts for attaching a 
strongback are held in place with templets of 2x4 and 2x6. 


2. The concrete is being placed and screeded. 


3. The concrete has stiffened sufficiently to permit the temp- 
lets to be removed and the surface leveled with a darby. This 
panel has a metal window frame cast in it. The other two 
openings are simply framed with 2-in. material. 


4. and 5. The surface is finished by troweling and 
brushing. 


10 


6. The panel is being tilted into position after which it 
will be braced as are those in the background until the 
columns are cast. 


7. Here is the other side of the tilting panel. The work- 
man is placing the mortar on which the panel is set. The 
2x4 wales attached to the foundation are used to align 
the bottom of the panel. 


8. The dowels have been wrapped with paper to prevent 
bond with the cast-in-place concrete column. The lifting 
bolts in the panel at the left have been removed. The 
bolt hole will be filled with mortar. Such patches are 
always darker than the cast concrete unless part of the 
regular cement is replaced with white cement. 


9. The column forms are in place for casting the columns 
which is the final operation. 


Grade beams are being cast on the 
ground. Fill will be placed against 
these slabs in their final position so 
that the rough finish on the bottom is 
not important. 


CONSTRUCTION DETAILS 


Casting Surface 


The concrete floor slab generally serves as the casting 
platform, but occasionally a stationary wooden platform 
or a tilting platform has been used. Grade beams which 
must be made before the floor is placed have frequently 
been cast directly on a leveled area of ground. 

The ideal platform is a level, smoothly troweled con- 
crete slab. Pipes or other utilities to be extended upward 
through the floor slab may be stopped below the floor 
surface and the openings temporarily closed. The closure 
may be made by a flush wood plug, by filling with sand 
topped by a thin coat of mortar, or by any means which 
will give a flush surface. It should be remembered that 
any imperfections in the surface of the casting platform 
will show on the wall panel. If the floor has a decided 
pitch or depressions, it may be leveled with sand topped 
with a thin mortar coat or with a lean soil-cement fill. 
These temporary toppings are easily removed after the 
panels are raised. 


Bond Prevention 


Many materials have been used satisfactorily to pre- 
vent bond between the floor and the wall panels, but 
some have given consistently better results than others. 

Bond-preventive materials may be divided into two 
general groups: sheet material and liquids. The latter 
are by far the more generally used. 


12 


Sheet Material. While paper and felt effectively pre- 
vent bond, they should not be used where the contact 
surface of the panel is to be left exposed or simply 
painted. At least a few wrinkles invariably occur in the 
paper and disfigure the surface of the panel. Paper and 
felt often stick to the panel and in some cases are diffi- 
cult to remove. Paper or felt impregnated with asphalt 
or having a layer of asphalt may stain the panels. 


Sheets of plywood, tempered fiberboard and metal, 
when oiled or otherwise properly treated, are effective in 
preventing bond and may be reused many times when 
handled with reasonable care. Their disadvantage is the 
initial cost and the joint marks left on the wall panels. 
The marks may not be objectionable if they occur in a 
regular pattern. 


Canvas gives a very pleasing texture and has been 
used successfully where the panels are lifted at a very 
early age as can be done with vacuum lifting mats. After 
concrete has hardened sufficiently for handling the pan- 
els by other methods, it is very difficult to remove the 
canvas even though it has been treated. The canvas 
should be dusted with cement or sprinkled with water 
just prior to placing the concrete. 


Liquids. Some general rules apply to the use of all 
liquids used for bond prevention. A sufficient quantity 
must be applied to seal the floor surface and prevent 


x Fillet for all 
edges flush with 
- columns 


bond with the wall panel. A considerable excess should 
be avoided as it tends to discolor the wall panel. The ma- 
terial should be applied in two or more coats. The first 
coat or coats should seal the floor surface completely and 
leave no dry spots. The final coat should be applied only ; 
a relatively short time before the concrete is placed so os @ ee 
that material and workmen will not scratch or scuff the ee : : 
final film. Marks and footprints on this film may show 
on the finished panel. The material may be applied with 
a swab, brush or spray. 


"x 4"Brace 


Sometimes different materials are used for the first ae : : ET Cage form ‘Notch for 
coat and final coat. As an example, curing compound has . . ae a © 
been used for the first coat and spirit wax for the final : 0 : 


coat. 

The liquid must be kept off reinforcement so that bond 
between the concrete and reinforcement will not be re- 
duced. 

The common types of form oil have given good results 
when properly used. The concrete floor must be dry when 
the oil is applied and the oil must be allowed to dry before 
the concrete panel is placed. If the oil is not sufficiently 
dry it will float up into and stain the concrete and will 
not prevent bond. 

Several of the special form treatment materials have 
been used with good results. 

Curing compounds have been used very successfully 
on many jobs. The first coat should be applied as soon 
as the concrete floor has been finished and will then serve 
the dual purpose of assisting in curing the floor and of 


Edge Forms. A, B and C show basic arrangements of edge 
forms made of 2-in. lumber. Fillets as shown in A should be 
used wherever the face of the panel is flush with the column. 
Extra strips may be used as in D and E when offset edges 
are desired. Ripping and notching the edge form for dowels 
and bolts as in F permit easier stripping than boring holes 
even though they are considerably oversize. 


Liquid soap has been satisfactory but requires spe- 
cial care to be sure the proper amount is used. In some 


breaking the bond between floor slab and wall panel. 

A special spirit wax has been used on several jobs 
with excellent results. Ordinary liquid floor wax has also 
been used successfully. 


cases an excess of soap has reacted with the fresh con- 
crete so that the finished surface of the wall panel has 
been sandy. 

There are also materials specifically prepared for this 


Simple forms can be used for corner 
columns which are flush with the 
wall surface on both the inside and 
outside. On this job the two pieces 
of plywood for the outside column 
faces are fastened together with an 
angle screwed to the plywood and 
are handled as a unit. The plywood 
is stiffened between ties with a 2x4. 
A 2x4 and 2x6 fastened together 
and handled as a unit are used for 
the inside form. 


13 


-2°x 4’ Blocks, | 
Bolted for 


Plywood — 


Temporary a 


spreaders " 


KI \Doubie 2’«G'wales- 


endtorm tes 


LZ 
ZX 


ny 


purpose. Some of these have given excellent results and 
in certain parts of the country are used practically to the 
exclusion of other materials. 

Some job-mixed materials have also given good re- 
sults. Among these is a mixture of 5 lb. of paraffin in 1 
to 1% gal. of light oil or kerosene. The oil must be heated 
to dissolve the paraffin. 


Forms 


Forms for the sides of panels are usually made of 2-in. 
lumber but in a few cases steel angles or channels have 
been used. 


14 


- Chamfer strips tacked to forms after fo: 


are temporarily braced in place 


ra 
3 + 
x5 


Mel _-—1 or 2 lines 
i oe 2x 6" W 


Column Forms. Column forms which can be easily erected, 
stripped and reused are of importance to economical tilt-up 
construction. These few typical details may be modified to 
fit many conditions. A wire through a hole near the end of 
the temporary spreaders will aid in and assure their removal. 


Regardless of the material used, edge forms must be 
sufficiently stiff and well braced to remain in good align- 
ment. This is particularly true of those forming the top 
and bottom edges of the panel. When side edges of pan- 
els are completely encased in cast-in-place concrete, any 
irregularities in these edges will be covered by the col- 
umns. The top of the forms should be in the same plane 
so that they can be used for screeds. 

Edge forms for the sides must have holes for the 
dowels which extend into the columns. The holes should 
be % in. larger than the dowels to permit easy stripping. 
Sometimes the forms are split on the line of these holes 
to make removal easier. 

For doors and windows, the finished frames or rough 
bucks may be cast in the panels, or openings may be pre- 
pared by using forms similar to those for the panel edges. 
The frames or forms are held in place by fastening to 
the edge forms or by loading them with sandbags or 
heavy blocks of concrete. 

When wood frames or forms are to be used, provisions 
should be made in forming all openings in the panels so 
that swelling of the wood will not start corner cracks in 
the concrete. Where the dimension of the opening is not 
more than about 4 ft., a piece of edge grain lumber in 
the corner will absorb enough of the expansion of the 


Special precast concrete units have been 
used to replace exterior column forms and 
to give the same surface texture as the 
panels. In the middle of the photo to the 
left is a newly cast unit. The surface which 
will be exposed is on top so that it can 
be finished the same as the wall panels. 
The unit in the foreground shows the wire 
loops which hold the unit in place tempo- 
rarily and tie the unit to the cast-in-place 
column. In the background is a stockpile 
of the units. The photo at the right shows 
the column forms ready for placing the 
concrete. Tierods extend through holes cast 
in the tilt-up panels. The difference in color 
of the tilt-up panels and the precast column 
form is due to the difference in age and 
moisture. The color was uniform by the 


frame to prevent cracking. For larger openings, the ex- 
pansion can be absorbed by a splice in the frame. This 
is made by cutting diagonally through the frame and then 
lightly nailing the pieces together. 

Although many steel window frames are cast in the 
wall panels there are several advantages in placing the 
frames after the concrete has hardened even though there 
may be a slight increase in cost. This is particularly true 
in moist climates where the steel may rust and cause dis- 
tortion of the frames or spalling of the concrete. In such 
climates, frames cast in the concrete should have at least 
a coat of paint applied on the job in addition to the shop 
coat. 

Many methods are used to keep edge forms from 
spreading. They may be tied together by %-in. rods and 
form tie fittings or by wire running between opposite 
edges in the plane of the reinforcement or they may be 
braced on the outside. The latter is more common. The 
forms for panel sides can be braced against the sides 
of adjacent panels. Frequently column bars projecting 
above the floor can be used to brace the form for the top 
and bottom edges. Inserts or temporary bolts set in the 
floor slab can be used for bracing the forms and later 
for attaching temporary braces to hold the tilted panels 
in position. Considerable stiffness can be added to edge 
forms by backing them with 2-in. members laid flat on 
the floor or blocked up to form a T or channel. Where 
there is considerable repetition of the panel sizes, the 
stiffening members may be nailed to the edge forms so 
that they can be handled as a unit. 

Temporary wood ties or braces may be nailed across 
the top of the forms until the concrete has been placed. 
These are particularly helpful in keeping the corners 
square. 


time the job was completed. 


Reinforcement 


As mentioned in the sections on design, the walls 
must be reinforced as conventional reinforced concrete 
walls and also to provide for the stresses due to lifting. 
The reinforcement may be supplied in the form of bars 
or welded wire fabric or a combination of the two. 

When welded wire fabric is used, bars must be used 
as dowels between the wall panels and the columns. Even 
with bar reinforcement, some contractors prefer to use 
extra bars for dowels. This permits the reinforcement to 
be assembled as mats outside the forms and placed in 
the forms as a unit. Mats can be assembled rapidly on 
a jig and the use of mats greatly reduces walking on 
the floor which has been treated with the bond preventive. 
If wire fabric is used in panels with openings, it is usually 
placed in sheets covering the entire area and then clipped 
along the edges of the openings. 

As with any reinforced concrete construction, a large 
number of small bars gives better crack control than the 
same weight of larger bars. However, the small bars cost 
slightly more per pound and require a little more time 
to place. 

Extra reinforcement should be used at openings. The 
bars may be parallel to and about 2 in. from the sides of 
Openings or may be placed diagonally across the corners 
of openings. Diagonal bars interfere less with concrete 
placing in walls cast flat than in those cast in place. They 
are also somewhat more efficient than parallel bars in 
preventing corner cracks. The minimum extra reinforce- 
ment should be one %-in. bar extending at least 2 ft. 
beyond the corners of the opening. 

The reinforcement may be supported in the conven- 
tional manner used for floor slab reinforcement or may 


ie 


16 


Blocks of concrete, which have proved very useful on tilt-up 
jobs, are being used here to hold window and door frames 
in place and to hold the side forms in alignment. This reduces 
the amount of bracing and thus saves considerable time and 
material as well as reducing interference with placing and 
finishing the concrete. A rod slipped through the two loops 
on the blocks permits two men to handle them easily. These 
are much more satisfactory than sand bags which sometimes 
are used in a similar manner. 


be suspended from members laid across the edge forms. 
These temporary supports may be removed before final 
screeding of the concrete so as not to interfere with this 
work. Steel chairs should not be used when the bottom 
surface of the panel will form the outside face of the wall. 


Utilities 


Electrical conduits and outlets can be placed in the 


forms and cast in the concrete. Where there is a horizontal 
run across two or more panels the conduit can be ex- 
tended through the edge forms the same as dowels. There 
are several compression-type fittings which can be used 
to connect the conduit from adjacent panels in the column 
space. The conduit and outlets can be held in place dur- 
ing the placing of the concrete by wiring and wedging 
them to the reinforcement. 


Concrete 


Quality. The concrete must be of a quality which 
will withstand weathering and so should contain not 
more than 6% gal. of water, including surface water 
carried by the aggregate, per sack of cement. Since the 
concrete is placed with the panels in a horizontal posi- 
tion, a stiffer mix and larger size aggregate can be used 
than in walls cast vertically. A minimum of 5 sacks of 
cement per cubic yard of concrete with 1'2-in. aggregate 
should give a satisfactory mix. 

Placing. The concrete is placed and finished the same 
as in a floor slab. Extra care should be taken to prevent 
honeycomb along the bottom edges of the form and to 
prevent breaking through the bond-prevention material. 
The concrete is worked into place by spading or by vi- 
bration and is then screeded, floated and finished, using 
the same technique as for floors. The compaction and 
screeding may be combined by using a vibrating screed. 
A mechanical float is advantageous for finishing wall 
panels as well as floors. 

Wall finishes. Many different finishes may be ob- 
tained economically when the wall is cast in the hori- 


The walls of this Sears Roebuck and Co. retail store at Portsmouth, Va., are 8 in. thick including 2 in. of insulating concrete. 
The troweled exterior surface of the tilt-up panels is patterned by cutting with a center bead. The parapet wall is cast in place 
with the columns and has control joints at the center of each panel. F. E. Davidson was the architect and the concrete work 
was done by W. F. Magann Corporation. 


Left—Schaubs Market, Temple City, Calif. F. Thomas Collins, engineer. Wohl-Calhoun Co., contractor. Right—Warehouse and 
office of Nunn Electric Supply Corporation at Houston, Texas. C. A. Newsome and L. S$. Newsome, architects. Harold Van Buskirk 
and Co., contractors. 


zontal position. Some of these are: smooth float, swirled 
float, hard troweled, brushed or broomed, patterned, 
colored and ground. Regardless of the finish used, work- 
men must be cautioned to do the finishing of all panels 
and all parts of each panel in a uniform way. A spotty 
effect will result if, for example, part of a panel is 
troweled more than other parts. 

Many variations of float finishes may be obtained 
exactly the same as on floors and sidewalks. A fairly 
smooth float finish catches less dirt than a rougher fin- 
ish. Troweling gives a smooth surface but increases the 
possibility of surface crazing and magnifies inequalities 
in finishing. In severe climates, the surface may gradually 
lose this smoothness on the most severely exposed por- 
tions so that a uniform appearance will not be retained 
over the entire surface. The grout-cleaning procedure 


described under “Column finishes” is advantageous on 
trowel-finished panels also. 

A pleasing finish may be produced by drawing a brush 
or broom over the trowel finish. This tends to minimize 
any irregularities in the surface and removes laitance 
which may cause surface crazing. The amount of scoring 
or roughness may be varied considerably by varying the 
stiffness and coarseness of the brush or broom, the pres- 
sure on the brush, and the hardness of the surface at 
the time of brushing. Having the brush marks in the 
vertical rather than the horizontal direction of the panel 
reduces the collection of dirt and increases the washing 
effect of rain on the walls. For this reason any horizontal 
brushing should be very light. 

Patterns may be made by cutting the surface with a 
center bead. A checkerboard effect may be obtained by 


Here are three of the many tilt-up jobs built by the William P. Neil Company in Los Angeles from designs prepared by Reliance 
Engineers, Inc. In the foreground is the office and warehouse of General Electric Company. Next is the Hudson Sales Corporation 


and then Westinghouse Electric Corporation. 


combining the pattern with the brushed finish and lightly 
brushing adjacent sections in different directions. 

Color may be obtained by adding a colored concrete 
topping before the base concrete hardens. Of course, 
the building can be painted but it must be remembered 
that once painted it must be repainted periodically to 
retain good appearance. 

A ground finish may be given wall panels when in 
the horizontal position. The same methods are used as 
in finishing terrazzo floors. 

Column finishes. A great variety of surface finishes 
are possible on wall panels, but the number of practical 
variations on the columns is quite limited. This should be 
considered in connection with the overall architectural 
effect. The most common finish on columns is the smooth 
surface obtained by using forms of plywood or other ma- 


Warehouse of Stanley Home 
», Products at Tulsa, Okla. C.R. 

; Nuckolls, engineer. Horster, 
., contractor. 


terial in large sheets. Accentuated vertical board-marked 
surfaces can sometimes be used effectively. Fluting is 
also readily obtained by tacking milled wood strips on 
the inside of the forms. 

The simplest, most economical and satisfactory final 
treatment for columns is a grout cleaning of the surface 
as follows: 

Mix 1 part portland cement and 1% parts fine sand 
with sufficient water to produce a grout having the con- 
sistency of thick paint. White portland cement should 
be used for all or part of the cement in the grout to give 
the color desired. Wet the concrete enough to prevent 
absorption of water from the grout and apply the grout 
uniformly with brushes or a spray gun, completely filling 
air bubbles and holes. Immediately after applying the 
grout, float the surface with a cork or other suitable float, 


Warehouse of Merchants Transfer and Storage 
Co., Des Moines, lowa. The wall panels for 
this 3-story building were cast on tilting plat- 
forms. After the first story walls were com- 
pleted, the second floor was cast and then the 
cycle repeated for the second and third stor- 
ies. Brooks and Borg, architects and engineers. 
Weitz Company, Inc., contractors. 


scouring the wall vigorously. All excess grout should be 
removed by finishing with a sponge rubber float. This fin- 
ishing should be done at the time when grout will not be 
pulled from holes or depressions. Next, allow surface to 
dry thoroughly, then rub it vigorously with dry burlap to 
completely remove any dried grout from the surface. 
There should be no visible film or grout remaining after 
this rubbing. The entire cleaning operation for any area 
must be completed the day it is started. No grout should 
be left on the surface overnight. 

Curing. Curing of panels should be started as soon 
after finishing as possible without marring the surface 
and should be maintained until the concrete has attained 
the desired strength. Attention should be given to any 
possibility of staining or discoloration from curing, since 
even a slight amount is objectionable and will not wear 
away evenly on the vertical wall surface. The possible 
effect on bond for painting should also be considered. 


Joints 


Various materials and details have been used in mak- 
ing the horizontal joint between the wall panel and its 
supporting member. The most common material is port- 
land cement mortar, but premolded joint filler has also 
been used either alone or in combination with mortar. 

The simplest method of using mortar is to spread a 
layer of it on the foundation and tilt the wall onto the 
mortar bed. This gives a strong, watertight joint. The 
principal objection to using mortar is that the mortar 
may squeeze out unevenly and there is little opportunity 
for adjusting the level of the wall. With some details 
of columns and roofs, a small variation is not important. 
A refinement of this method is to place carefully leveled 
pads or blocks on the foundation. These will hold the 
panel at proper level until the mortar sets. The pads 
may be replaced by wedges which can be used to true 
the panel as it is being placed. 

Another procedure is to set the panel on pads, blocks, 
or wedges and then fill the joint with mortar dry-packed 
into place. This permits easy and good adjustment of the 
panel but the expense of dry-packing is considerably 
more than spreading plastic mortar. Although some be- 
lieve a tighter joint can be obtained by dry-packing, very 
careful workmanship is required to obtain a good job. 

Sometimes the panel is set on a strip of premolded 
joint filler about 12 to % the thickness of the wall and 
the remainder of the joint is dry-packed. This permits 
quick setting of the panels and results in a tight joint. It 
has the disadvantages of not permitting adjustment of 
the panels and of being relatively expensive. 

Joints similar to ship-lap or tongue-and-groove have 
been used but such joints are unnecessary and add to 
the cost. 

Another needless detail which adds to the cost is the 


19 


fe filler or 


Seay IgG “9 Os 
-:O | Insulation |°> 970 


Foundation—Wall Joints. These are typical joints subject to 
many variations. A and C are the simplest and most com- 
monly used. The offset from the floor level in D and the offset 
in the wall in E are to reduce the possibility of leakage. How- 
ever, if the foundation or lower wall is sloped or offset slightly 
as shown in these sketches so that there is no horizontal 
surface to catch the water, there is little possibility of leak- 
age. Certainly there is no more possibility of leakage at 
this point than with any unit masonry wall. 


use of a hinge to prevent the slab from sliding during 
erection. If the lifting force is applied vertically there is 
no tendency for the panel to slide and even if the lifting 
force is at a slight angle there will be little or no sliding. 
If the lifting equipment is such that there is a consider- 
able horizontal component, this can be offset by attach- 
ing snubbing lines to the dowels near the bottom of the 
panels. Hinges have the disadvantage of making it im- 
possible to adjust the alignment of the panels after plac- 
ing without cutting the hinges. Also, they may split the 


The panel will be tilted onto the strip of premolded joint filler 
and then the remainder of the joint pointed with cement mor- 
tar. 


A enn Cone 39.3 


a oo Reinforcement lapped or welded— ce 
and ©) to be used on 


- €losure and not where co 
€) stiffness is required 


asa 
umn 


Column—Wall Joints. A to D are typical joints for use where movement at the joints is desired. They can also be used for rigid 
joints by lapping the reinforcement and omitting the bond-prevention material. Note that even where movement is desired at 
intermediate columns the corner columns are bonded to the wall panels. V-joints should be used wherever the face of the 


wall is flush with the column. 


concrete from the edge of the panel. If hinges are used 
they must be set with extreme accuracy. 

To eliminate the possibility of leakage, too much em- 
phasis is often placed on the making of this horizontal 
joint rather than on other details. Any of the joints men- 
tioned above will be at least as watertight as the usual 
joint between masonry walls and their supports. To pre- 
vent leakage it appears that emphasis should be placed 
on other details. The supporting member should not ex- 
tend in a flat plane even a fraction of an inch beyond the 
face of the wall. If there is any extension, it should be 
sloped so that any water running down the wall will drain 
away from the joint. 

Normally rain will not penetrate very far into a ver- 
tical joint or crack even though it may be relatively wide. 
If, under severe conditions, rain does penetrate into the 


20 


crack and runs down, no damage will be done if it drains 
outside of the building at the bottom of the joint. Trouble 
may develop, however, if any water accumulating at the 
bottom of the vertical joint drains into the building rather 
than to the outside. To reduce this possibility, the top of 
the floor may be an inch or so above the horizontal joint. 
Experience has shown that with such an offset, panels 
can be tilted into place without difficulty. 


Columns 


There are probably more variations in column details 
than in any other feature of tilt-up construction. Columns 
may be placed either after or before the panels are tilted. 
Both methods have their advantages. On the large ma- 
jority of jobs, however, the columns are cast after the 
panels are in place. This permits the use of simple and 


economical details and, since it is not necessary to have 
such exact dimensions as required when the columns are 
placed first, less care is required in forming and placing 
the panels. This is particularly true where the column 
overlaps the wall panel on both faces. The column form- 
ing is more economical when the panels are placed first. 
Casting the columns first has the advantage of eliminat- 
ing or greatly simplifying the temporary bracing of pan- 
els and thus reduces the cost of bracing and time of 
erecting each panel. 

Another major point of variation is whether the rein- 
forcement or dowels from adjacent panels are fastened 
together or are arranged for relative movement. On the 
west coast, where earthquakes are considered in the de- 
sign, adjacent panels are fastened together as rigidly as 
possible. Rigid connections have also been used through- 
out the country in residences and other small structures 
where the walls are not more than one or two panels 
long. For larger buildings in parts of the country where 
it is not necessary to design for earthquake forces, nearly 
all column connections are designed to allow relative 
movement between adjacent wall panels. This permits 
expansion and contraction of the panels, caused by 
moisture and temperature changes, without developing 
stresses which would tend to crack the walls. A survey 
of buildings constructed by the tilt-up method has shown 
that there is movement in the majority of joints between 
panels and columns and that cracks in the panels are 
extremely rare. 

Where the columns are cast after the walls are in place, 
they may overlap the panels on one or both sides. This 
overlap hides any irregularities in the panel edges and 
variations in the planes of adjacent panels. Even though 
the space between panels may vary because of inaccura- 
cies in panel dimensions or setting, the overlap permits 
uniform column width and repeated use of the column 
forms without adjustment. The possibility of leakage is 
also reduced by the overlap. 

The overlapping edges of columns must be prevented 
from bonding with the wall panels to allow movement 
in the joint without cracking the lip. If the surface of the 
panel covered by the lip is smooth and true, bond can be 
prevented by coating it with any of the materials used 
for bond prevention in casting the panels. Under other 
conditions a membrane of some type should be used. 
This may consist of one or two thicknesses of paper, felt, 
premolded joint filler, cork gasket or similar material. 
This may be cemented to the panel to hold it in place 
during concreting. It may extend beyond the form and 
be trimmed off even with the lip after the forms are re- 
moved or, with rigid or semirigid material, it may be 
butted tightly against the form before placing the con- 
crete. 

It is sometimes desirable to have the column flush 


Concrete for the columns is being delivered by a hopper bot- 
tom bucket on a crane. The column form is used to support a 
platform from which the workmen can guide the bucket and 
rod or vibrate the concrete in the column. 


with the panels on one or both sides of the wall. In such 
case a V-joint or other definite rustication should always 
be used between the wall panel and the column. This 
rustication will hide and protect the crack which will 
form at this point; permit calking if necessary (quite 
unlikely); give a straight, true joint; prevent smearing 
of panels with leakage from concrete cast in the column; 
and break the wall surface so that variations in the planes 
of adjacent panels will be inconspicuous. 

Where the panels are tied together rigidly by cast-in- 
place columns, the reinforcement from adjacent panels 
should be welded or lapped sufficiently to develop by 
bond the tensile strength of the bars. 

The bars from adjacent panels, where relative move- 
ment is desired, must be coated or covered to prevent 
bond. If deformed bars are used, they must be wrapped 
with paper or some other material to be certain of pre- 


21 


The warehouse for Westinghouse Electric Supply Corporation at Toledo, Ohio shows the contrast between horizontally board- 
marked columns and steel troweled and tooled panels. Albert Hutchison, engineer. Henry C. Beck Company, contractor. 


venting bond. Where plain bars are used as dowels, bond 
can be prevented by coating them with waterproof grease, 
bituminous material, or with the bond-prevention mate- 
rial used in casting the wall panels. The portion of the 
bars which is to extend into the column can be dipped 
into the liquid bond-prevention material before the dow- 
els are set in the panels. Before the concrete is placed 
in the columns the bars should be checked to see that 
they are perpendicular to the plane of the edge of the 
column and wall panel, and are completely covered or 
coated. Some care must be used in placing the concrete 
to prevent removing the coating or covering. Since these 
bars will act in shear only, they need not extend very far 
into the column to develop their full strength. In some 
cases this extension has been as little as 2 in. although 
about 6 in. is more common. It should be sufficient to 
extend them just beyond the column reinforcement. A 


me 


short extension gives satisfactory results, saves steel, re- 
duces the possibility of bond and gives less interference 
with tilting. 


Roofs 


Any type of roof can be used with tilt-up construction. 
The problem of waterproofing the top of the joint be- 
tween columns and panels is eliminated if an overhang- 
ing roof is used. Although the movement at these points 
is so small that it will not affect any type of roof con- 
struction it may be sufficient to cause trouble from leak- 
age unless precautions are taken. The most common and 
simplest treatment is to use calking compound in the 
joint between column and panel. This performs satisfac- 
torily when properly maintained. Where the wall extends 
above the roof, a continuous raggle should be cast in the 
wall and columns for the roof flashing. 


This 15 ft. by 15 ft. by 6 in. panel is being tilted with pickup points 
at the top. The sling is attached to a 6x6 angle bolted to the top edge. 
Space for the bottom leg of the angle was formed by a well-oiled 
strip of plywood. The strongback in the foreground was used on panels 
having large openings. The workman at the left is placing the mortar 
upon which the panel will be set. The panels are held in position tem- 


porarily by 2x10 struts and airplane cable with turnbuckles. The 
cables are attached near panel top as it is being raised so that work- 
men need not leave the floor. In the background are part of the forms 


used for the cast-in-place architectural concrete front of the building. 


TILTING 


Equipment 


Tilting may be done with simple hand-operated equip- 
ment or with various kinds of power equipment up to 
large specially designed cranes. The choice will depend 
upon the size of the job and the cost and availability of 
equipment which the contractor owns or can rent. For 
small jobs where only a few panels can be made ready 
for tilting in one day, some contractors have found it 
more economical to use hand equipment with a higher 
labor cost than to bring in power equipment. Where a 
considerable number of panels are ready for tilting at 
one time, power equipment will speed up the job and 


generally prove more economical. Any equipment can be 
used which can give both vertical and horizontal move- 
ment either simultaneously or alternately. 

The most popular power equipment is a crane. Other 
equipment used includes a winch and A-frame either on 
the ground or mounted on a truck, specially designed 
hydraulic jacks and even power shovels. In some locali- 
ties a specially designed crane with a vacuum mat for 
handling tilt-up panels is available for rental. 

Although it is desirable for lifting equipment to have 
a capacity equal to the weight of the panel, this is not 
necessary. Work can be done with equipment which has 
a capacity equal to little more than one-half the weight 


23 


of the panel. Capacity above this acts as a safety factor 
and is useful in aligning the panel in case it is not tilted 
into the exact position desired. Even with a minimum 
lifting capacity, considerable adjustment of final position 
can be obtained by jacking or by prying with a pinch bar 
or timber. 


Tilting 

Power tilting equipment may be operated from either 
inside or Outside the building. Each position has its ad- 
vantages and disadvantages. The selection will depend 
upon the specific job conditions and equipment available. 


This steel angle will be attached to the panel by the bolts 
projecting from the top edge to aid in distributing the lifting 
stresses. 


This hand-operated tilting mast is simple and inexpensive. 
On small jobs the cost of extra labor involved is more than 
offset by the saving in cost of equipment. The short 6x6 angle 
used for attaching the equipment to the panel does little to 
distribute the pickup stresses indicating that any method of 
direct attachment to the top edge is satisfactory with small 
panels. A slight modification for wider lateral distribution 
of pickup load would be advantageous. 


Operation from inside the building provides a smooth 
even surface for the equipment but heavy equipment 
may overstress the floor where it is designed for only 
light loads. This difficulty has been overcome on large 
buildings by casting only that portion of the floor needed 
for a casting platform. On small buildings, tilting from 
the inside causes more interference with other work on 
the job and conversely other construction operations or 
material storage may interfere with movement of the 
equipment. Working from the inside places the equip- 
ment in the most advantageous position when the great- 
est lifting force is required. This occurs when the lifting 
starts, at which time the boom is practically vertical 
rather than extended at an angle as is necessary when 
the equipment is outside the building. 

The leads from the lifting equipment should be kept 
practically vertical at all times to avoid sliding the panel 
on the slab. There will then be no need for hinges or 
other devices to prevent sliding. 

The vertical alignment of the panels can be checked 
with a spirit level attached to a straightedge about the 
height of the panel. A plumb bob can also be used as a 
simple and easy way of checking vertical alignment. Be- 
fore the panel is raised, the plumb line is attached to the 
top of the panel so that it will hang a couple of inches 
from the face of the wall. This distance is measured accu- 
rately before tilting. After the panel is raised, its plumb- 
ness can be checked by measuring the distance from the 
line to the face of the wall at the bottom. 


Lifting Attachments 


There are many satisfactory ways of connecting the 
panel to the lifting equipment. In making a selection for 
a particular job, consideration should be given to the 
lifting equipment; size of panel; openings in panel; lift- 
ing stresses; cost of material and installation of inserts, 
etc.; cost of reusable material; and time required to at- 
tach and detach lifting equipment. 

The simplest connection is made by making a 180 deg. 
hook in the end of two of the vertical reinforcing bars in 
the panel and having part of these hooks protrude from 
the top edge of the panel. This detail has been used satis- 
factorily for panels as much as 12 ft. in height. With 
small panels the sling from the hoist may be fastened 
directly to these hooks. Fastening the hooks to a rigid 


24 


A vacuum pad is used as the attachment to the panel. This 
reduces the stresses in the panel and does not disfigure the 
surface. An extra line is attached to the top edge of the 
panel as a safety measure and can be used to handle the 
panel after it is tilted. In some instances, pads have been 
used which cover nearly the entire surface thus practically 
eliminating bending stresses in the panel while tilting. 


cross member or spreader to which the sling is attached 
will reduce the bending stresses in the longitudinal direc- 
tion of the panel. This longitudinal bending may be min- 
imized by bolting a channel or angle to the top edge of 
the panel and attaching the sling to it. Channels or angles 
may also be bolted to the edges of the panel to reduce 
the bending in the vertical direction of the panel. 

Splitting of the concrete by lifting bolts or hooks in the 
edge of the panel should be prevented by placing a rein- 
forcing bar in the panel parallel to and about 2 in. from 
the edge. 

The equipment that has been used most frequently to 
reduce lifting stresses in the panel is a strongback. While 
there is a growing trend to eliminate the use of strong- 
backs because of the attachment bolts in the finished wall 
surface and also because experience has shown that pan- 
els can be lifted without them, many contractors continue 
to use them. The strongback usually consists of 2 legs 
extending from top to bottom of the panel and a cross 
member near the top. The legs are bolted to the slab at 2 
or more points and the sling is attached to the ends of 
the legs or to the cross member. Each leg consists of a 
deep I-beam or 2 channels, back to back, with spacers. 
Channels are preferred since they can be attached to the 
panel with a single bolt at each attachment point while 
the I-beam requires 2 bolts at each point. The extra bolt 
adds to the cost of material and placing, and has the dis- 
advantage of further disfiguring the wall. 

A strongback which can be easily adjusted to a wide 
range in size and shape of panel can be constructed for 
very little more than a nonadjustable one. Suggested de- 
tails for such an adjustable strongback are shown at 
right. Even though such a strongback is to be used, 


Extra I-beams have been welded on top of the legs of the 
conventional strongback to increase their stiffness. Extra 
connections between the panel and the spreader are made 
through plates at the edge of the panel. The 4x4 timbers 
attached to the foundation wall guard against the panel 
slipping off the foundation while being tilted. All of these 
details may be useful but are not generally necessary. 


considerable time and money will be saved by locating 
pickup points on any one job so that the strongback can 
be used with as few changes in adjustment as possible. 

Strongbacks are generally attached by removable bolts 
embedded in the concrete, the nuts remaining in the con- 
crete. To permit removal, the bolts must be coated or 
wrapped. Form lacquer or similar material is preferred 
to oil or grease for coating since the latter may cause 
slight surface staining. The material is easily applied by 
dipping. Giving the bolts a half turn within 24 hours after 
the concrete is placed will aid materially in their final re- 
moval. Ordinary bolt stock is seldom perfectly round 
which sometimes makes it difficult to remove and replace 


Strongback. A strongback such as this permits easy adjust- 
ment to fit panels of any size. The pickup points can be any 
place on the vertical legs, the legs can be moved horizontally 
on the spreader and the spreader can be moved along the 
legs. The sling can be attached to the spreader at various 
points by moving the links and bolts. 


i Lean bolted or | 
}, welded back to back jj 
with spacers | 


them for attaching the lifting rig. This can be overcome 
by using stud bolts which are not removed from the con- 
crete until the panel is in place. 

Some contractors have used form ties rather than bolts 
for attaching strongbacks. These are economical and give 
a minimum of disfiguration to the wall surface. 

Vacuum mats have been used very satisfactorily for 
picking up panels. They can be located on the panels so 
as to give negligible lifting stresses, thus permitting early 
tilting and minimum reinforcement. The surface will not 
be disfigured by bolt holes. 


The three-point pickup part way 
down the panel shown in this 
view reduces bending stresses. 
The hooks near the top of the rig 
clamp over the top of the wall 
and steady it during setting. Half 
columns are cast integrally with 
and at the edges of each panel. 
The half columns are fastened to- 
gether at the top and grout placed 
between them. The reinforcing 
bars extending from the panel 
will join with bars extending from 
the floor slab and then concrete 
will be cast to complete the strip 
of floor slab along the wall. No- 
tice the slots rather than holes in 
the attachments for the braces 
lying on the panel in the fore- 
ground. 


Braces 


As with all other details of tilt-up construction, there 
is great variation in the methods of bracing the panels 
until the columns are cast. Braces vary from a 2x4 with 
simple attachment to the top of the wall and to the 
ground or floor, to pipes with adjustable length and spe- 
cial fittings at the ends. In selecting the braces to be used, 
consideration should be given to safety, speed and ease 
of use, initial cost and number of reuses. 

From the safety standpoint, consideration should be 
given not only to preventing the panel from being blown 


Three special hydraulic jacks op- 
erated in unison were used to tilt 
this panel. Snub lines attached 
to the top of the panel prevented 
it from tilting too far until the 
wood braces were secured. 


26 


ip 
ee 


B 
® 
= 

i 
s 
va 
ra 
- 


This elaborate arrangement of equalizers can be used to 
advantage on long panels but is not needed for the average 
job. Two sets of attachment points on each cross member 
provide for some variation in pickup points. 


down, but also to the safety of the men during erection. 
Obviously it is best if the workmen have little or no work 
to do on the top of the erected wall to attach the braces. 

The wood braces with simple end connections at first 
appear to be the most economical but this is not always 
true if the overall job is considered. The special braces 
with some means for close adjustment of length, such as 
a turnbuckle type, and with special end connections can 
save considerable time in plumbing the panel and in at- 
taching and detaching the braces. With some types, the 
top connection can be made before the panel is in an up- 
right position. The time saved in attaching and plumbing 
is particularly important because it means a saving in 
time of the erection crew and equipment used on each 
panel. With the turnbuckle type, accurate plumbing can 
be done while the lifting rig is being fastened to the next 
panel. 


Bolts for attaching a strongback are held in position by a 
templet during placing of the concrete. Many times bolts and 
inserts can be held in place satisfactorily by wiring to the 
reinforcement although a templet will usually result in more 
accurate positioning. 


Insert 
Ty or bolt 


plank fastened 
to floor 


Pipe bent , 
i : Cand flattened 
‘Opening 
24 in wall 


Right and 
left hand 
threads 


Braces. Sketches A to | show typical connections of braces 
to walls and J to M show connections to the floor. Any of these 
may be combined or used with other details such as stakes 
driven into the ground. For economy, braces must be set and 
adjusted quickly after the panel is tilted. The fine adjust- 
ment possible with turnbuckles such as shown in N and O 
result in rapid erection and release of tilting equipment 
before final plumbing of panels. The turnbuckles, being rela- 
tively weak in bending, should be placed near the end of 
the brace. 


27 


28 


Adjustable Braces. 

1—A pipe brace with a great adjustment in length. The top section telescopes 
into the lower section and the two are held together with a bolt. The holes 
for this adjustment can be seen in the upper piece of pipe. Fine adjustment 
is made with the turnbuckle at the bottom. 

2—A close-up of the standard turnbuckle. 

3—A turnbuckle attached to the end of a timber brace. 

4—An adjustable brace in which the pipe, with nuts welded to the ends, forms 
a turnbuckle with the eye bolts at the ends. Beyond this pipe brace can be 
seen two timber braces with metal connections at the end. 

5—Another type of adjustable pipe brace. The threaded portion is stiffer than 
the standard turnbuckle, so it can be placed nearer the center of the brace 
without materially reducing its stiffness. It is more convenient for workmen 
when placed at this height. 


Six-in. tilt-up walls are 
combined with a cast-in- 
place architectural con- 
crete front on this Grange 
Cooperative Wholesale 
warehouse at Spokane, 
Wash. Designed by T. 
Carson and built by L. E. 


Blumer Company. 


escapees 


sg 


— INSULATION: 


As in other types of construction, the heat insulation 
value of tilt-up walls may be increased by the use of fur- 
ring, blanket insulation, rigid insulation and plaster in 
the usual manner after the wall is erected. It may also 
be increased by using lightweight concrete and, of course, 
by increasing the thickness. Other ways are by casting 
the panel on rigid insulating board which bonds to the 
panel; using lightweight aggregate concrete for the in- 
terior face of the panel; and making the wall as a sand- 
wich with insulating material between the two layers 
of concrete. 

Nailing strips are usually cast in the panel when the 
wall is to be insulated in the conventional manner after 
tilting. 

When concrete is cast on rigid insulation the bond 
may be increased by driving nails through the insulation 
so they will protrude into and bond with the concrete. 
If the insulation does not give a satisfactory wall surface, 
plaster may be applied after the wall is in place. 

Part of the wall thickness (inside face) may be made 
of concrete having a high insulating value, such as that 
made with aggregates of very light weight. If the inside 
face of the wall is the bottom of the panel, the insulating 
concrete is placed and screeded to the desired thickness. 
A delay of 2 to 4 hours is necessary before placing the 
regular concrete to prevent its penetration into the insu- 
lating concrete. Finishing and erection then proceed in 


the usual manner although extra curing and drying be- 
fore tilting have proved worthwhile. To avoid crushing 
or spalling the bottom edge during tilting, it is desirable 
to use the regular concrete for the entire thickness of the 
panel for a distance of about 2 in. from the bottom edge. 
A 2-in. plank temporarily set inside the bottom edge 
form can be removed after the insulating concrete has set 
and will thus provide space for the regular concrete. The 
thickness of the insulating concrete will depend upon the 
insulation desired. From | to 6 in. has been used in pan- 
els with total thickness of 6 to 8 in. However, about 2 in. 
of insulating concrete will provide sufficient insulation 
in most cases. 

The insulating concrete, of course, will not withstand 
the abrasion and bumping that will occur in some occu- 
pancies. A finish coat of plaster may be applied to the 
wall which will give the conventional plaster surface. 

The sandwich-type panels are made by placing a layer 
of concrete, a layer of insulation and then a layer of con- 
crete, the last two layers being placed before the first one 
has hardened. Reinforcement is placed in both layers of 
concrete and the two layers are fastened together by ties. 
These may be single bent bars or wires or may be strips 
of mesh or expanded metal. Sometimes the strips are 
bent to form a channel or Z-section. The insulating ma- 
terial should bond to but not be adversely affected by 
the fresh concrete. It should also act as a vapor barrier. 


Zo 


if ie 


~~ 


Warehouse at South Bend, Indiana. Both the 19- 
ft. high walls and the 60 ft. span rigid frame 
bents were tilted into place. Precast purlins sup- 
port a precast concrete roof deck. Place & Com- 
pany, owner and contractor. William S. Moore, 
engineer. 


Grandstand at Richardson, Texas. The bents and walls, 
except parapet, are of tilt-up construction on this econom- 
ical grandstand. The treads and risers are of L-shaped 
precast units. Chappell, Stokes and Brenneke, engineers. 


30 


Trench silo on W. D. Caldwell farm, Prairie City, 
lowa. A continuous steel channel was slipped 
over the top of the tilt-up panels to keep them in 
line and was anchored to concrete deadmen on 
outside of silo before backfill was placed. The 
temporary inside braces supported the wall dur- 
ing backfilling and were removed as the silage 


was placed. cen 


QW al oat 


Warehouse for St. Louis Waste Material Company at Fort Worth, Texas. The 
lower part of this reinforced concrete thin-shell roof was precast on a nearby 
platform, lifted into place and made an integral part of the cast-in-place 
structure. Precasting reduced the formwork and eliminated the difficult plac- 
ing of concrete between forms. The upper part of the shell was cast in place 
with formwork on the underside only. Bailey Company, engineer-contractor. 


Grain storage building at Jordan, lowa. This 60x180-ft. build- 
ing with tilt-up walls is for bulk storage of grain. Temporary 
bulkheads are placed inside the doors as the building is filled. 
William N. Nielsen, architect-engineer. A. Sterner Company, 
owner-conftractor. 


A few of the 37 grain storage bins with tilt-up walls being 
built by the Grain Processing Corporation at Muscatine, lowa. 


31 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program 
of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. | 


PRINTED IN U.S.A. ; / $3 


Riverside Baths, Sacramento, California. W. E. Coffman, architect. 


FOREWORD 


’ ; ‘HE great popularity of swimming has caused an increasing demand for information 


concerning the financing, design, construction and operation of public, private and 
club pools. Previous editions of this booklet have contained material on these subjects, 
but in order to present the latest information based upon the experience of pool design- 
ers, builders and operators, this completely revised edition has been prepared. 

The material contained is intended to aid in the preliminary development of swim- 
ming pool projects, to assist the designer in the preparation of final plans and speci- 
fications for a satisfactory pool, and to help the operator in conducting the pool in an 
efficient and profitable manner. For the greatest economy in construction and opera- 
tion, the design and construction of each pool should be under the supervision of an 
architect or engineer experienced in such work. 

Some of the information given is of a general nature because the individual pool 
must be considered as a special problem, and all recommendations and data, espe- 
cially those concerning planning and financing, cannot be made universally applicable. 
Supplementary information relative to specific problems on many of the subjects treated 
broadly in this booklet is available upon request. 

If you have questions on swimming pool construction or operation not answered 
in this booklet, write us. We shall be glad to be of service. 


PORTLAND CEMENT ASSOCIATION | 33 West Grand Avenue, Chicago 10, Ilinois 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, tech- 
nical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold 
program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, 


engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. 


CONCRETE SWIMMING POOLS 


Financing, Design, Construction and Operation 


INTRODUCTION 


PAGING pool is an investment in health and 
happiness. Swimming has long been considered 
one of the most healthful and beneficial sports. Ancient 
Romans believed that a long daily swim was the best 
cure for insomnia! Early French monks believed it the 
best tonic for body and soul! Present-day physicians 
also believe in the benefits of swimming. The contribu- 
tion of swimming in aiding the treatment of infantile 
paralysis victims is known to all. 

Swimming under proper conditions is healthful, but 
under bad conditions may subject the individual to 
hazards of disease and accident. With the concentra- 
tion of population, the water of the “old swimmin’ 
hole” has, in many cases, become unfit for swimming. 
The new pool with its modern water purification sys- 
tem eliminates the danger of the spread of disease. 
The carefully designed and operated pool also removes 
the accident hazards inherent in the unsupervised 
swim in the river, lake, or quarry. 

Adequate swimming facilities encourage beneficial 
exercise and tend to diminish juvenile delinquency by 
providing a positive influence for good. 

It is the duty of public officials to protect the health 
and welfare of the public. Inasmuch as modern swim- 
ming pools aid in these functions, the officials respon- 
sible for their construction will receive the thanks of 
the public. 

A swimming pool attracts non-residents, resulting 
in more business for local merchants. 

To the club a swimming pool offers an increase in 
membership, club activities and income. Many coun- 
try clubs have proved conclusively that a new swim- 
ming pool has been responsible for an increase in 
membership. Activities have been increased not only 
by the addition of new members but also by old mem- 
bers and their families spending much more time at 
the club while one or all use the swimming pool. 
Members who formerly came only for a round of golf 
now bring the family, have a swim, and stay for 
dinner. The first year the pool was in operation at one 
golf club, the dining room and bar showed the first 
profit in the history of the club, rather than the usual 
deficit which had been as high as $4,000 a year. The 


importance to the younger members of the family of 
providing healthful recreation in good environment 
must not be overlooked. 

A swimming pool provides an ever-ready supply of 
water which would be extremely valuable in case of 
fire. This water can be used by a fire department 
pumper or, at a slight cost, an auxiliary pump may be 
provided to furnish pressure at convenient hydrants. 

The private swimming pool adds distinction to the 
home, brings pleasure to the family and makes the 
home the center of healthful activity. For the residence 
away from the city water supply, the pool also pro- 
vides fire protection. 

Hotel owners find that a swimming pool attracts 
guests. It appeals to those who enjoy strenuous exer- 
cise, to those who would while away idle hours, to the 
bored and the sophisticated, and to the masses who 
simply enjoy swimming. Even where the hotel is 
located on a natural body of water, a swimming pool 
will prove popular because of the purity of the water 
and the clean and attractive surroundings. 


THE PROJECT 


A swimming pool should be considered as an inte- 
gral part of a complete development. This applies to 
the small private pool as well as to the large municipal 
pool although all the factors are not the same. To 
obtain best results, it is necessary that the whole 
project be under supervision of someone experienced 
with such developments and that under his direction 
the parts of the plan be developed by specialists. 

Ordinarily there will not be much question as to 
whether the pool will be indoor or outdoor. Where 
this question does arise, some of the points to be con- 
sidered are: length of outdoor season compared to 
all-year use; desire to swim in open during summer; 
comparative cost of indoor and outdoor pools of same 
capacity; additional cost of operation during winter. 

A complete development for a public swimming 
pool should include, in addition to the swimming pool 
or pools, a wading pool, bathhouse, spectator facilities, 
and play area. 

Wherever possible, a wading pool should be in- 


The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in 
the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working 
drawings should be prepared and approved by a qualified engineer or architect. 


cluded with every public or semi-public pool. For the 
sake of safety, the wading and swimming pools should 
be completely separated either by a fence or by a 
considerable ground area. 

The bathhouse, of course, is an important part of a 
swimming pool project. The success of the develop- 
ment will depend in no small part upon a satisfactory 
bathhouse, which is discussed on page 20. 

Adequate provision should be made for spectators. 
Their presence may form an extra source of revenue 
by collection of a small spectator fee or may simply be 
considered as advertising and good-will development. 
Suggestions for these facilities are given on page 20. 

Many people want some type of entertainment 
between swims. The pool will prove much more popu- 
lar if a play area is provided. If space and funds are 
available, it is wise to furnish facilities ranging from 
simply an area for sun bathing to the strenuous sports. 
The play area, in addition to its drawing power, will 
have the effect of increasing the pool capacity by 
keeping more people busy outside the water. 

Sun bathing is very popular and should be encour- 
aged by suitable facilities. The easiest construction to 
provide and maintain is simply a concrete-paved area. 
This may be terraced so that the sun bathers can have 
a better view of the pool. Sand areas are quite popular, 
but must be carefully maintained to keep them sani- 
tary and attractive. The use of a coarse sand with an 
adequately drained concrete slab underneath will 
assist in keeping the sand in good condition. Most 
operators and health authorities insist that the sand 
area be separated from the pool and that a shower be 
taken when returning to the pool area. To be effective, 
the showers must discharge a large volume of water. 
Grass areas are even more difficult to maintain than 
are sand areas and should not be considered except 
for private pools. 

Games which can easily be used in connection with 


swimming pools and offer wide variety of physical 
activities include: outdoor checkers, shuffleboard, 
paddle tennis, badminton, handball, tennis, basketball 
and weight lifting. A concrete dance floor with a 
coin operated record player is also popular and income 
producing®. 

In a large part of the country, the outdoor pool can- 
not be used for swimming during several months of 
the year. Where there is a long period of freezing 
weather, the larger pools may be used for ice skating. 
In the non-swimming season, pools may be used for 
roller skating and various games such as those sug- 
gested for game areas. Large wading pools and the 
swimming pool of multiple-unit pools are particularly 
well adapted to these extra uses. Such multiple use of 
swimming pool facilities is especially desirable be- 
cause it takes advantage of a fixed investment and 
extends its usefulness. 

An indoor pool can be used the year around for 
swimming but, in addition, it may have a movable 
floor so that the entire pool room can be used as an 
exhibition hall such as that in the Earl’s Court Exhi- 
bition Building, England. Other pools. in England 
have been constructed so that part of a large outdoor 
pool is enclosed for winter use. Another method of 
making dual use of facilities is the construction of a 
large outdoor pool and a smaller indoor pool using the 
same water treatment plant and dressing facilities. 

The outdoor pool will require more room for dress- 
ing facilities than the smaller indoor pool. In winter 
the extra dressing space may be used by patrons of the 
gymnasium, if such is included. If there is no gym- 
nasium, the excess space may be turned into a recre- 
ation room or small gymnasium. 

*References are made in footnotes throughout this booklet to 
other publications issued by the Portland Cement Association 
containing additional pertinent information which will be sent 


free upon request in the U.S. and Canada. Information on play 
court construction is available. 


Fire protection is the primary purpose of this reservoir at New Orleans Airport. Designing water reservoirs as 
swimming pools makes them serve a double purpose. 


FINANCING 
Publie Pools 


There are many ways of financing public pools. 
Popular sentiment is generally so strongly in favor of 
the improvement that little difficulty is experienced in 
securing the money necessary for construction. A 
properly designed and operated pool is not a drain 
on the public treasury. By charging reasonable fees, 
the pool may be not only self-supporting but self- 
liquidating, if desired. This subject is discussed more 
fully on page 24. 

Public pools are ordinarily constructed and managed 
by the park board of the city government. General 
funds of such bodies are sometimes sufficient for the 
construction of the pool, while in other cases general 
bonds may be issued. In some states, revenue bonds 
can be issued for such projects. These bonds are 
simply a lien on the income from the pool. 

Where all the necessary capital cannot be obtained 


This self-supporting municipal pool at Washington, Indiana, in- 
cludes a sand beach separated from the swimming and wading 
pools by a fence and open air shower. John H. Kretz, architect. 


Public campaigns may be conducted to secure out- 
right donations, or to sell advance admissions in some 
form. Where donations are solicited, most of the funds 
will be obtained from a relatively small number of 
people. If admissions, reduced rates, or other induce- 
ments are offered, a great many more people will 
respond to the appeal for funds. 

While funds for pool construction can be raised by 
sale of advance admissions, the problem of operating 
expenses must not be overlooked. The advance sale, 
of course, means that regular day-by-day receipts will 
be materially reduced and that some special provision 
must be made for operating expenses during the time 
advance tickets are being redeemed. If income from 
the pool is intended only to pay part of the expenses, 
the admission fees during the first year may be made 
somewhat higher than considered necessary in later 
years after expiration of the tickets sold in advance. 


This view of Astoria Park swimming pool shows how New York 
City Department of Parks uses large pools during non-swimming 
months for games such as basketball, paddle tennis, handball 


If the pool is to be self-liquidating, payments on the 
principal may be set to begin after the advance 


and shuffleboard. 


from park or city sources, all or part may be raised 
by public contribution. Labor, equipment, materials 
and professional services, as well as cash, are frequent- 
ly donated. Thus, everyone can help and the task of 
raising funds to build the pool is minimized. 

Civic clubs, chambers of commerce, and American 
Legion posts throughout the country have conducted 
many successful campaigns for community swimming 
pools. Sometimes several of these organizations have 
combined to conduct the campaign. They have thus 
rendered a valuable service to their community in 
contributing to the welfare and pleasure of its citizens. 


tickets have expired. 

Various benefits sponsored by the committee or 
other organization may comprise part of the public 
campaign to raise funds. These may include all sorts 
of athletic events, theatrical performances, concerts 
and exhibitions. 

Im some instances where public funds were not 
available, pools have been built by private capital 
with the understanding that they were to become 
public property after a certain number of years or 
after the pool had made certain returns to the builders. 
With such an arrangement, pools can be built on 
public land, thus reducing the private capital needed 
and permitting the public to own and control the pool 
at an earlier date. 


A quiet, secluded pool owned by the designer, Edward Honnert, 
Cincinnati, Ohio. 


Club Pools 


Club por may be built with funds from the general 
treasury by bonds secured by the entire club. 
gener ek general club funds are usually not 
available and it may be difficult to finance construc- 
tion by a general bond issue. The most common 
practice is to form and incorporate within the club a 
Pool Association which will handle financing, con- 
struction and operation of the pool until finances are 
such that the project can be completely taken over 
by the club. 

In order for the Association legally to build and 
operate the pool, it is customary for the two organiza- 
tions to have a contract which includes the inter- 
relation of the two and the leasing of the ground for 
the pool to the Association. 

The Association may finance the pool in whole or 
in part by a bond issue. If the bonds are for only a 
small part of the cost, they may be sold through 
banks or other ordinary financial channels. If the 
bonds represent the major cost of the pool, it will 
probably be necessary to sell them to members of the 
club. Bonds should be subject to retirement as fast 
as income will permit. It will often be necessary or 
desirable to offer some special inducement to pur- 
chasers of bonds, such as an option on club member- 
ships at a specified fee during a certain number of 
years. 

Another method of raising funds is by the sale of 
memberships in the Pool Association. Such member- 
ships are ordinarily limited to members of the club, 
but under some circumstances are extended to out- 
siders with certain restrictions. Memberships entitle 
the holders to use of the pool at reduced rates for a 
specified number of years. 

Season tickets are also a common method of obtain- 
ing funds for club pools as well as public and com- 
mercial pools. With this method, provision must be 
made for operating expenses if the cash daily admis- 
sion fees are not expected to cover them. 


6 


SELECTION OF SITE 


The general location of a public or commercial pool 
will materially affect its success. To obtain the most 
patronage, the pool should be easily accessible by 
foot, public transportation and automobile. Parking 
space for autos must also be considered. Existing 
parks are generally fairly well located to meet these 
requirements. By using property already publicly 
owned, the cash outlay for the pool will be reduced. 

An adequate water supply and suitable drainage 
must also be considered in selecting both the site and 
the location of the pool on the site. 

Where property must be purchased for the pool, 
it will generally be found that the most desirable 
location from the standpoint of accessibility and 
facilities is more expensive than some outlying loca- 
tion. It then becomes necessary to balance the in- 
creased cost of the best location against the increased 
patronage that may be expected. 

In municipal developments, the public will gener- 
ally be served better by constructing two or more 
pools of reasonable size in different parts of the city 
than by constructing one extremely large pool. The 
initial cost and operating costs will be somewhat 
increased so that the extra convenience and increased 
use must be balanced against the increased cost. 

The advantage of several small pools over one large 
pool applies even more to wading pools than to 
swimming pools. Most of the children using wading 
pools are attended by their mothers, so that locations 
within walking distance of the homes are desirable. 

After the selection of the site comes the exact loca- 
tion of the pool on the property. In a complete park 
or recreational development, the location of the pool 
will be made with reference to the other facilities. 
Wherever possible, the pool should be located so that 
it is protected from the prevailing winds by the bath- 
house, a wall, a hedge or some other windbreak. A 
very satisfactory encloure is made by forming a ridge 
with the material excavated from the pool and plant- 
ing a hedge on top of it. In some cases it will be advis- 
able to locate the pool so as to provide some shade 
although, in general, sunshine is highly desirable. 

Trees will provide a picturesque setting but are 
generally a nuisance. Falling leaves make it difficult 
to keep the pool clean and the roots may clog the 
drainage tile and push sidewalks out of position. 

It is preferable to have the bathhouse along the 
shallow part of the pool so that poor swimmers will 
not dash from the bathhouse into the deep water. If 
the filtering equipment is located in the bathhouse, 
there may be a slight saving in cost by placing it 
near the deep water, but the safety feature should 
not be sacrificed for this small saving. 

At country clubs the pool should be so located that 
the noise from the bathers will not disturb the golfers, 
particularly those on the putting green. It should be 
easily accessible from the regular dressing rooms. If 
the pool is not enclosed, it should be located so that 
people in street shoes will not ordinarily use its walks. 


SIZE 


Size of the proposed pool is a very important ques- 
tion which should be determined only after careful 
consideration of several important factors. The pool 
should have sufficient area to accommodate the largest 
number of people who may be expected frequently 
during the season, but it should not be designed for 
the maximum number who may be expected only a 
few times a year. It must not be so large as to be 
wasteful of water or space under ordinary conditions, 
or to appear poorly patronized. It is better to have 
the pool too crowded a few times each season than to 
have it so large that operating costs are excessive. The 
available building site and the amount of money which 
can be raised for the purpose will also have an im- 
portant bearing on the size of the pool. 

Where studies show that attendance will justify a 
large area pool, there is a growing tendency to con- 
struct separate pools for diving and swimming. This 
eliminates much of the danger of accidents between a 


between 5 and 10 per cent of the population. Another 
rule is to consider the average daily attendance as 2 to 
3 per cent of the population. Maximum daily attend- 
ance will generally be 2 to 6 times average daily 
attendance. Maximum attendance at any one time 
seems to be about one-third the daily attendance. 
Combining these values shows that the attendance at 
any one time on the maximum days will be about the 
same as the average daily attendance. Designing for 
this attendance should give a pool of sufficient size for 
maximum days and of very generous size for average 
days. These methods of computing attendance are for 
public outdoor pools and should be considered only as 
rough guides where better information is not available. 


Area 


The most common methods of determining the 
capacity of pools are those of the Joint Committee*, 
which base the capacity upon both the surface area 
and upon the water volume and treatment. 


diver and someone in the water. It also makes the The capacity based on surface area considers that 


ols easi olice. ag ar arere ; ’ ; 
Bee ee) Douce *Report of Joint Committee on Bathing Places of the American 


Public Health Association, 1790 Broadway, New York 19, N.Y., 
and the Conference of State Sanitary Engineers. 


Attendance 


In determining the size of a pool, the first thing to 
be done is to estimate the attendance. This is not so 
difficult for a country club or other private or semi- 
private pool, but it is quite difficult to make an accu- 
rate estimate for a public pool. There are no fixed 
rules for estimating attendance at a public pool. A 
careful study by an experienced pool designer is neces- 
sary. Some of the points to be considered are: climatic 
conditions, local habits and customs, accessibility, 
competition from other pools and admission fees. 
Experience of pools in simlar situations is one of the 
best guides. The operation of the pool will also have 
a very great effect upon the attendance. 

A study by Iowa State College has shown that the 
size of the city has considerable influence on the pro- 
portion of total population which will attend the pool. 
The smaller the community the larger the proportion 
which will use the pool. The study indicated that for 
cities under 30,000, maximum daily attendance will be 


Dusk lends added enchant- 
ment to the pool at the 
Edgewood Valley Country 
Club, LaGrange, Illinois. 
The precast concrete fence 
separates bathers and 
spectators. Straight wall 
sections provide for turn- 
ing at ends of racing lanes. 
Wesley Bintz, designer. 


The T-shape is used to 

separate the divers and 

bathers at Riis Park pool 

of the Chicago Park Dis- 

trict. Note the large pro- 

portion of bathers using 
the shallow water. 


each swimmer and bather requires a certain area in 
which to move. The area where water is more than 
5 ft. deep is considered as swimming area and that of 
lesser depth as bathing area. Considering that only 
part of those in attendance will actually be in the 
water, it has been decided that 27 sq.ft. of deep water 
or 10 sq.ft. of shallow water is required for each person 
in attendance at one time. Water less than 3 ft. deep 
cannot be used effectively by the average person. 

It is assumed that each diving board may be used by 
12 persons at one time, part of these being in the water 
and part awaiting their turn to dive. Since the area 
required for each diving board is about 300 to 400 
sq.ft., the area for each diver is about the same as for 
each swimmer. 

Experience with large outdoor pools has shown that 
about 75 per cent of the area should be less than 
5 ft. deep. For pools of this proportion the above 
requirements give an average over the entire area of 
12 sq.ft. for each person in attendance. 

Where wide walks and play areas are provided, the 
proportion of patrons actually in the water will be 
considerably reduced, so that the pool area allowed for 
each patron may also be reduced. This factor is recog- 
nized in the method of computing capacity which 
allows each bather 20 sq.ft. of combined pool and 
walk area. 


Volume 


The bathing capacity of the pool is limited by the 
water content and the amount of clean water added, 
as well as by the surface area. Clean water includes 
both fresh water and treated recirculated water. 

The Joint Committee and many states specify that 
the total number of bathers using a pool during any 
period shall not exceed 20 persons for each 1,000 
gallons of clean water added during that period. 
Where the addition of disinfectant is not continuous 
during the bathing period, the total number of persons 
using the pool between disinfections should not ex- 
ceed 7 for each 1,000 gallons of water in the pool. 

Under these Joint Committee regulations, in pools 


The multiple-unit 
pool in Washington 
Park, designed and 
built by the Chicago 
Park District. Gen- 
eral pool, left; com- 
petition pool, right; 
diving pool, right 
rear; and wading 
pool at the rear out- 
side the pool en- 
closure. Concrete 
grandstand for spec- 
tators is easily main- 


tained. 


of ordinary proportions and with a complete water 
turnover period of 8 to 12 hours the bathing load 
generally will be limited by the surface area rather 
than the water supply. However, the water supply or 
circulation should always be checked, since it may 
be the controlling factor, particularly in pools having 
a continuous series of classes and in those having a 
very large proportion of shallow water. 

With the old type “fill-and-draw” pool (see page 17) 
the water volume and disinfection becomes very 
important even for the small private pool, which is 
about the only type now being built with this system. 
Applying these requirements to a pool of 8,000-gallon 


capacity, ae 20 or 160 persons could use the pool 


before changing the water, but the pool should be 
disinfected after use by seed <7 or 56 bathers and 
again for every 56 additional bathers. 

Another method of determining bathing capacity 
for recirculating pools is described in Minimum Sani- 
tary Requirements for Swimming Pools and Bathing 
Places, issued by the Department of Public Health, 
State of Illinois. Under these regulations the bathing 
load is determined from the formula: 

CxXM 
BL= Ts 
in which BL is the maximum number of bathers 
daily, C is water content of pool in gallons, T is time 
in hours required to recirculate the entire content of 
the pool, and M is an arbitrary multiple depending 
upon many factors including: indoor or outdoor pool; 
width and drainage of walks; use of suits and caps; 
use of private suits or suits laundered after each 
use; enforcement of cleansing bath before using the 
pool; efficiency of recirculating system; and general 
arrangement of bathhouse and pool surroundings. This 
coefficient usually varies between 2 and 6. With a 
reasonably well-designed and operated outdoor pool, 
the coefficient will be about 2 when there is no suit 


control, and 3 when only regulation suits laundered 
after each use are worn. 


SHAPE 


Pools of rectangular shape are the most common 
and generally the most satisfactory, but there are 
some advantages to circular, oval, and irregular- 


shaped pools. 


Rectangular pools are simple to design and con- 
struct. They are also superior to other shapes for the 
conduct of swimming meets since they provide uni- 
form racing lanes with good ends for turning. If meets 
are to be held in oval pools, temporary bulkheads, for 
which provision should be made in the original design, 
must be erected for starting and turning. 


Round or oval shapes have been used for large pub- 
lic pools. The advantages claimed are: by providing 
shallow water around the entire perimeter of the pool, 
the danger of nonswimmers falling into deep water is 
eliminated; the volume of water is less than for rec- 
tangular pools of the same area, thus costing less to 
operate; and the construction cost is less. The dis- 
advantages are: the difficulty of holding competition; 
the additional cost of the diving platform and waste 
of the expensive deep area of the pool used by the 
platform; the greater volume of water and increased 
cost of construction and operation if proportions of 
deep and shallow areas are the same. 


Recently several pools have been constructed of 
special shapes intended to improve operation. Some 
of these are of L or T shape with the diving in the 
stem of the T or one leg of the L and swimming in 
the remainder of the pool. Oval pools have also been 
built with one side modified to provide for diving, 
rather than having the diving platform in the center. 

A few irregular-shaped pools have been built to fit 
the contour of the ground or for architectural reasons. 
In some pools the simplicity and stiffness of completely 
rectangular pools has been modified by curves at one 
or both ends. 

Swimming meets of some kind will be held in 
practically all but private pools, even though they are 
not originally contemplated. Therefore, such meets 
should be given some consideration in the design. 

The national and international organizations con- 
trolling swimming meets and records are quite liberal 
in the specifications for the length and width of pools. 
Three sets of records are recognized. One set is for 
pools 60 ft. to 75 ft. in length; another for pools 


75 ft. to 150 ft.; and a third for pools more than 150 ft. 
in length. 

There are certain convenient lengths which provide 
an even number of laps for recognized contests. Some 
of these convenient lengths are 60 ft., 75 ft., 25 meters 
(about 82.5 ft.), 100 ft., 150 ft., and 165 ft. (55 yd. or 
slightly more than 50 meters). The actual length of 
the completed pool must be the full nominal length, 
not even a fraction of an inch less, or records made 
therein will not be recognized. It is wise to build the 
pool 1 or 2 in. longer than the nominal length. 

The width should provide at least four racing lanes 
having a minimum width of 6 ft. A greater lane width 
is desirable. The width of large pools may be equal 
to one of the convenient lengths mentioned above so 
that races may be held across the pool. In this case, 
either the length or width may be in meters and the 
other dimension in yards. 

In marking the bottom of the pool it should be 
remembered that the competitor swims over the line 
and not between lines. For important meets it is desir- 
able to have surface lane markers as well as lines on 
the bottom. Attachments for such markers should be 
cast in the walls. The width of exterior lanes may be 
the same as interior lanes, but this must be the clear 
width without any obstructions such as ladders. 

If a pool is to be built primarily for competitive 
meets, more attention should be given to the require- 
ments and recommendations of the controlling athletic 
organizations than is necessary for the average pool. 
The suggestions given here are for pools in which 
meets will be held only occasionally. 


DEPTHS 


As with the length and width of pools, the athletic 
authorities have few fixed limits on the depth. The 
water must be at least 3 ft. deep and the starting 
platform from 18 in. to 30 in. above the water. To 
assure 3 ft. of water, the overflow should be a few 
inches more than 3 ft. above the pool bottom. 

There are no strict rules for depth of water under 
diving boards, nor is there unanimity of opinion on 
this point. However, the best opinions seem to be that 
absolute minimum depths should be 8 ft. for the 
l-meter board and 91% ft. for the 3-meter board. 
Greater depths are desirable, particularly under the 
3-meter board and some authorities give this minimum 
as 11 or 12 ft. Most common depths are 10 or 11 ft. 


The recreation center at 
Nazareth, Pennsylvania, 
Borough Park includes this 
swimming pool with curved 
ends and a circular wading 
pool at the right of the 
bathhouse, of hollow con- 
crete units, Edwin H. Jones, 
architect. 


LEGEND 


5-Water depth 


[Zia \ Meter springboard 


3 Meter springboard 


20' 


Within the wading depth of water, up to 
about 5 ft., there should be no steps or steep 
slopes. The Joint Committee gives the maxi- 
mum slope as | to 15, but considerably steeper 
slopes have been used satisfactorily in small 
pools. A definite slope for all parts of the floor 
will aid in keeping it clean. 

The longitudinal section of most pools for 
swimming and diving is in the form of a spoon. 
This provides the proper depths with the 
greatest economy. In the past it has been 
customary to make the cross-section practical- 
ly level except in the larger pools. Recently 
the floor at the deep end has been sloped from 
the sides as well as the ends, thus forming a 
hopper bottom which saves excavation and 
reduces the depth of side walls. It also aids 


Simelizs 
+ 


20' 


AY. 


in keeping the floor of the pool clean where 
the water for recirculation is withdrawn from 
the bottom of the deep end. The extra difficul- 
ty of constructing this type of bottom is slight. 

A recent development of the hopper bot- 
tom places the opening for the main drain 
parallel to the springboard rather than at 


Typical layouts. 


Location of the deep water and slope of the floor are 
fully as important as depth. Minimum allowable depth 
of deep water should extend outward about 4 ft. from 
the end of the board. The length of the board, the 
method of supporting it, and the design of the over- 
flow will all affect the distance from the end of the 
board to the face of the pool wall, which may be 
between 4 and 9 ft. but will ordinarily be 6 or 7 ft. 

The bottom of the pool may slope up quite rapidly 
behind this point and at the sides, but in front of the 
board the slope should be more gradual. The bottom 
may slope up to a water depth of 5 ft. at a point about 
30 ft. from the end wall for a 1-meter board and 40 ft. 
for a 3-meter board. 

These depths and areas of deep water should be the 
absolute minimum and greater depths and areas are 
preferred. 

Where separate pools are provided for swimming 
and diving, the depth of the swimming pool may vary 
from 3 ft. 3 in. to 5 ft, and the depth of the diving 
pool will be governed by the height of the diving 
boards or platforms. 


10 


right angles to it. For pools having only one 
board, the drain is placed in line with it. If 
there is a high-board and one or two low- 
boards, the drain is placed in line with the 
high-board and the floor sloped up to the sides 
so that there will be sufficient depth under 
the low-boards. 


DESIGN 


Every pool should be designed by a com- 
petent engineer or architect to meet specific 
local conditions. 

Outdoor pools are usually built entirely in 
the ground, although a few have been built above the 
ground with the pool wall serving also as one of the 
walls for the bathhouse. This type has some advan- 
tages where the ground water is close to the surface. 

Indoor pools may be built in the ground, the same 
as outdoor pools, or in one of the upper stories and 
thus be supported by the building frame. In the latter 
case, special precautions should be taken to prevent 
uneven settlement of foundations and damage to lower 
floors caused by possible leakage or condensation. 


Forces 


Pools built in the ground should be designed to 
withstand the water pressure from within and to resist 
the pressure of the earth when the pool is empty. In 
general, it is inadvisable to consider the lateral earth 
pressure as aiding in resisting the internal water pres- 
sure. The type of soil and other local conditions will 
influence the selection of earth pressure to be used in 
the design. In some cases it may be necessary to con- 
sider external water pressure. 

To prevent the possibility of cracks forming as a 


result of temperature changes and shrinkage, it is 
necessary to provide sufficient reinforcement and cor- 
rectly designed expansion joints in the walls and floor. 
Adequate curing of high quality concrete will reduce 
the possibility of cracks. 


Subsurface Drains 


It is economically impractical to design the floor to 
resist much hydrostatic head or to resist the heaving 
action of frozen wet subsoil. Therefore it is essential 
that the pool have adequate subsurface drainage. The 
minimum drainage system that should be considered 
is a line of tile around the outside of all footings and 
a line under the deepest portion of the pool. For large 
pools there should be additional lines of tile under the 
pool. Where the subsoil drains very slowly, it will be 
advisable to place the floor on a bed of sand or cinders 
6 to 8 in. thick which has been thoroughly wetted, 
tamped and rolled. If cinders are used, all metal pipe 
passing through them should be encased in concrete 
to prevent corrosion. 


Structural Types 


The most common type of pool design consists of 
cantilever walls with separate floor. This type is simple 
to design and construct. A modification is the canti- 
lever wall with the base cast integrally with the floor, 
which gives a small saving in materials but is slightly 
more difficult to design and construct. 

Another type might be called beam-and-slab con- 
struction, in which the top of the wall and the side- 
walk are designed as a beam and the wall as a slab 
spanning between the beam at the top and the footing. 
The horizontal thrust on the beam is resisted by wall 
buttresses built between the beam and the footing. 

Small pools with the floor cast integrally with the 


Pp a It 
Sof On apes o. e 


aS 


CGI: Bene 
filler: copper dam 
SECTION 


Sidewalk and 
floor joint offset 
from wall joint 


Construction joint. |.) “5-P. 
Clean and bondin [hq 
accordance with 
section 14 of 
specifications 


ELEVATION 
WALL EXPANSIONG CONTRACTION JOINT 


Fill with mastic dam 


FOOTING-WALL CONSTRUCTION JOINT 
FLOOR-WALL EXPANSION& CONTRACTION JOINT 


walls may be economically designed as open top boxes, 
part of the stress in the walls being carried vertically 
as a cantilever and part horizontally as a beam sup- 
ported at the ends. 

The use of large slabs of cast stone as the structural 
wall as well as a finish has developed what might be 
called the structural frame type of pool. In this type 
the precast slabs span between columns or buttresses 
which transfer the horizontal forces to the footings. 
This construction is particularly fitted to pools in 
which colored walls are desired. 

Some pools have been built of shotcrete, which is a 
mixture of portland cement, sand, and water applied 
by compressed air. This method eliminates the use of 
forms on most of the work. Its use is limited to soils 
which can be shaped to the desired contour and which 
will retain this shape until the shotcrete is placed. 
Under these conditions the construction is quite satis- 
factory and economical. 


Minimum Sections and Reinforcement 


The thickness of walls and floors and the amount of 
steel will often be governed not by strength require- 
ments but by the minimum space needed for placing 
concrete and by experience. In general, walls of the 
cantilever type are not less than 10 in. thick, while 
those of the beam-and-slab type are not less than 6 in. 
The thickness of precast slabs is about 4 in. and floors 
are usually not less than 6 in. thick. 

The minimum amount of horizontal steel in walls 
will depend upon many factors, including expected 
temperature range, distance between joints, and qual- 
ity of concrete and methods of placing and curing. 
The least amount of horizontal steel in walls should 
be 0.0025 times the cross-sectional area of the wall. 
With good subsoil and drainage, about one-half this 
amount has given satisfactory results in floors. 


60 Bar diameters 


Extra dowels i 0.15 ee 
cross-sectional area of wall 


20 Gage copper 
dam or wood strip 


WALL CONSTRUCTION JOINTS 


20 eege bent copper 
optional) 


Trowel finish 
and cover with 


FLOOR EXPANSION & CONTRACTION JOINTS 


Typical expansion and construction joints. 


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LONGITUDINAL SECTION ON & 


Section CC 


CORNER DETAIL 


Suggested design for 30 x 75-ft. swimming pool. 


Joints 


Practically all pools contain either construction joints 
or expansion joints or both. The proper location, de- 
sign and construction of these joints are very important 
in obtaining a watertight pool. Construction joints are 
intended to be rigid and not allow movement, while 
expansion or contraction joints are intended to allow 
for the movement caused by changes in temperature 
and moisture content. 

Construction joints should be avoided as much as 
possible by planning the work so that a complete sec- 
tion between expansion joints may be placed in one 
continuous operation. However, it will generally be 
necessary to make a construction joint at the base of 
the walls. Such horizontal joints can be made satis- 
factorily by simply bonding the new concrete to the 
hardened concrete as described in Section 14 of the 
specifications. At such joints it is good practice to key 
the two sections by making a longitudinal slot in the 
center of the first section before concrete hardens. 

Vertical construction joints in walls should be keyed 
together and a water stop used, or extra dowel bars 
should be used equivalent in area to 0.015 times the 
cross-sectional area of the wall and extending 30 bar 
diameters on each side of the joint. 

Construction joints are seldom necessary in floors, 
but if required should be made the same as suggested 
for vertical construction joints in walls, or an expansion 
joint should be provided. Screeds must be removed as 
soon as possible and the space filled with concrete 
worked into the adjacent portion of the slab. 

The expansion joints in walls should be keyed and 
made watertight with water stops. Reinforcement 
should not extend across any expansion joint. 

Expansion joints in floors should be made over a 
beam or footing or some special type of joint used 
which will keep the adjacent slabs in line as well as 


12 


being watertight. The most common type of joint is 
made with a metal water stop and mastic fill. Where 
the ends of the slab rest on beams or footings, the 
water stop is frequently omitted and dependence for 
watertightness placed entirely on the filling and mastic 
between the slab and the footing or beam. The use of 
asbestos fibered mastic or multiple layers of open mesh 
burlap mopped with mastic will permit differential 
movement and assure the mastic remaining in place. 
Strips of soft clear grain wood may be used as filler 
between slabs. A layer of bentonite about 14 inch 
thick placed under the mastic in floor joints has been 
very effective in preventing leaks either in old or new 
ools. 

Offsetting the expansion joint in the floor about 1 ft. 
from wall joint will aid in making tight joints. 

The proper location and spacing of expansion joints 
must be determined for each job, and since there are 
no fixed rules for this determination, some general 
comments will be helpful. They should be placed 
where there will be the greatest tendency to crack, 
such as at changes in section or direction of members. 
For pools of regular shape, such points will be at the 
junction of floor and walls and where there is a sharp 
change in grade of the floor. The distance between 
joints should ordinarily not exceed 60 ft. However, 
a number of successful small and medium-size pools 
have been built without expansion joints. 


Openings 

There is always a tendency to crack where there is 
a reduction in section such as caused by holes for 
lights, pipes and other fixtures. For this reason extra 
reinforcement should be added at these points to make 
up for the concrete removed. The extra reinforcement 
should be about 0.015 times the cross-sectional area of 
the concrete removed and bars should extend about 
30 diameters beyond edges of the opening. 


Overflows 


Overflows were formerly called scum gutters and 
considered more or less as sewers, the water and other 
material which entered them being wasted directly to 
the sewer. This idea has been materially changed since 
it has been found that body wastes are distributed 
throughout the pool and that in a well-operated pool 
there is no collection of scum on the surface. There is 
a growing tendency to recirculate overflow water. 

Overflow gutters of many shapes have been used but 
gutters of the open type shown in the accompanying 
figure are preferred because they are the easiest to 
construct and to maintain. 

The entire overflow should be clearly visible and 
easily cleaned. Needless to say, it should be easy to 
construct. The overflow and walk should be so ar- 
ranged that water from the walk will not drain into 
the pool. The most definite way of protecting the pool 
from drainage is the use of curbs between the walk 
and the pool, however, with the open type overflow, 
any drainage from the walk will be intercepted before 
reaching the pool proper. If the walk is pitched to 
drain away from the pool as it should be in all outdoor 
pools, the slight amount of water which would drain 
into the overflow would not be serious, regardless of 
whether the water is recirculated or drains to the 
sewer. 

The overflows should have outlets at fairly close 
intervals and the bottom of the overflow should be 
definitely pitched, about 14 in. per ft., to drain to 
these outlets. The maximum spacing of outlets recom- 
mended by different authorities varies from 10 to 20 ft. 

The overflow may be discontinued for about 6 in. 
each side of expansion joints in the wall so that there 
will not be a joint through the overflow. 

Great care must be used in construction to see that 
the lip of the overflow is absolutely level around the 
entire pool. A surveyor’s level or water level should be 
used, as an ordinary hand level is not sufficiently ac- 
curate. 


Service Tunnels 


A number of pools have been built in which a serv- 
ice tunnel extends along one or all of the sides. The 
service tunnel allows quick and easy access to the 
piping and underwater lighting where such is used. 
Underwater observation booths, of assistance to coach- 
es, can be built as a part of these tunnels. 


Walks 


The walk areas around the pool are an important 
part of the development but are frequently given little 
thought. The surface should be non-absorbent, non- 
slip to bare feet, easy to clean, and sloped about 14 in. 
per ft. to frequent drains so that water will drain off 
quickly. In indoor pools where the only water on the 
walks is that from the pool, the drainage may be into 
the overflow. In outdoor pools, the drainage should 
always be away from the pool, except that where the 


overflow is not recirculated the walks are sometimes 
allowed to drain into the overflow gutters. There 
should be a curb at the outside edge of the walk to 
keep out dirt and litter. 

The entire pool should be surrounded by walks at 
least 4 ft. wide for interior pools and private outdoor 
pools and 12 ft. wide for other outdoor pools. The 
minimum clear width of walks should be maintained 
around diving and other recreational equipment. The 
width of walks should be increased for the larger size 
pools. From an operating standpoint, the width will 
never be too great. 

Providing ample areas around the pool will tend to 
reduce the number of persons in the water, which will 
be particularly advantageous when attendance is large. 

Although the surface must be non-slip, it should not 
be rough enough to hurt the feet. Satisfactory results 
may be obtained by using a brush finish, lift finish, 
or special abrasive aggregates. The brush finish is 
made by lightly brushing the surface with a fine hair 
brush after the final troweling. The lift finish is ob- 
tained after the final troweling by lifting the surface 
with some implement such as burlap or carpet fastened 
to a float. Special abrasive aggregates may be incorpo- 
rated into the surface by evenly dusting about 14 to 
\% Ib. per sq. ft. on the surface before troweling. 

Terrazzo containing an abrasive aggregate is deco- 
rative and effective for walks and other paved areas. 

Concrete that has been allowed to harden before 
being given a non-slip surface may be treated with 
muriatic acid. A 5 to 10 per cent solution is generally 
used. Drenching the surface with water before the 
acid is applied will keep the acid from soaking into the 
concrete and give a more uniform distribution. A lib- 
eral amount of acid solution should be scrubbed on 
with a stiff fiber brush and the surface then rinsed with 
clear water. More than one application may be neces- 
sary. 


Details of typical overflow gutters. Walks should be pitched 
to drain away from the pool. 


13 


Keeping walks clean will reduce slipping. Simply 
rinsing with water may not remove surface films which 
sometimes cause slipperiness. Such a condition may be 
eliminated by periodic scrubbing with abrasive pow- 
der or a detergent followed by thorough rinsing. Ordi- 
nary soap powders should not be used. 

To encourage frequent and thorough cleaning, there 
must be a sufficient number of hose connections so 
that all the walks can be reached with short lengths 
of hose. For adequate water volume and pressure, the 
piping and hose should be not less than 1 in. 


Quality Concrete 


A satisfactory swimming pool requires good quality 
concrete work. This depends upon the quality of ma- 
terials, ratio of water to cement, proportions of ma- 
terials, placing, and curing. 

Materials meeting requirements given in specifica- 
tions on page 26 will give satisfactory results. 

The watertightness, strength, durability and other 
desirable properties are dependent upon the water- 
cement ratio, which is the amount of water used with 
each sack of cement. For swimming pools, it is recom- 
mended that the concrete contain not more than 6 gal. 
of water—including that carried by the aggregate— 
to each sack of portland cement. 

The concrete must be of such workability and con- 
sistency that it will work into all of the forms without 
leaving voids or honeycombing or allowing free water 
to accumulate on top of the concrete. With a given 
water-cement ratio, the consistency is controlled by 
the proportions of cement, fine aggregate and coarse 
aggregate. The proportions will depend upon the max- 
imum size and grading of aggregates. Well-graded ag- 
gregates will give the best and most economical job. 
The exact proportions will depend upon the aggregates 
used and the method of placing and can be determined 
best by making trial batches. With average aggregates 
and hand placing, proportions will be approximately 
1 part portland cement, 21% parts fine aggregate, and 


14 


The Oak Park, Illinois, Country Club 
pool includes many modern features. 
The off-center hopper bottom economi- 
cally provides adequate depth for the 3- 
meter board. Inserts in the walk close to 
the pool make the erection of a guard 
chain a simple matter. The hedge around 
the walk will keep spectators out of the 
pool area, stop leaves and refuse from 
blowing into the pool, and will eventually 
serve as a windbreak for the bathers. 
Underwater and overhead lights not 
shown in the picture make night bathing 
safe and attractive. The recessed ladder 
is another safety feature. The pattern in 
the concrete walk is emphasized by 
brushing adjacent sections in different 
directions. Mayo and Mayo, architects. 


31% parts coarse aggregate measured by loose volumes. 
All materials should be measured accurately.* 

Concrete may be satisfactorily placed and com- 
pacted by hand spading, rodding and tamping or by 
mechanical vibration.* The latter method permits 
satisfactory placing with stiffer mixes than can be 
placed by hand, which reduces the shrinkage and gives 
a more economical mix. 

Curing is one of the most important yet most neg- 
lected factors in production of durable concrete con- 
struction. Curing increases the watertightness and 
strength of concrete and reduces shrinkage. Adequate 
curing is the most economical factor in improving the 
quality of concrete. Exposed surfaces should be kept 
continuously moist for a period of at least 7 days. 


SPECIAL FEATURES 
Finish 

Swimming pools may be finished in the natural con- 
crete color or any other desired color by one of several 
methods. Regardless of the color desired, the surface 
should be smooth and hard. Light colors are prefer- 
able to dark colors. 

If the concrete is to be left exposed, whether colored 
or not, the forms must be carefully made to give rea- 
sonably smooth surfaces. Immediately after the forms 
are removed, all projections on the exposed surfaces 
should be removed, any irregularities filled, the surface 
rubbed with carborundum and thoroughly rinsed.* If 
the forms are lined with large sheets of a smooth ma- 
terial, such as plywood or composition board, a smooth 
surface will be obtained with a minimum amount of 
work. 

The floor of the pool should be finished true to 
grade, and where the water is less than 5 ft. deep 
*Additional information on quality concrete and vibration is 
contained in Design and Control of Concrete Mixtures; Design of 


Concrete Mixes; Vibration for Quality Concrete; Finishing Archi- 
tectural Concrete. 


should have a float finish or non-slip surface as dis- 
cussed for walks. In deep water, a smooth troweled 
finish will aid in making the bottom self-cleaning. 

Colored pools may be obtained by use of paint, 
plaster, integral facing, terrazzo, cast stone or tile. 

For the floor of the pool, the most economical and 
satisfactory results will be obtained by using the 
“dusted-on” finish. The dusted-on mixture should be 
composed of 1 part of portland cement to 114 parts 
of dry sand and the required amount of pigment. 
After the floor has been screeded, this mixture should 
be uniformly spread at the rate of not less than 125 
Ib. per 100 sq. ft. of floor area and floated into the 
slab. White portland cement and silica sand applied 
in this manner are advantageous for the floor of the 
pool even if the walls of the pool are left in their 
natural color. 

Painting has been the most common way of obtain- 
ing colored pools, but before deciding to paint a swim- 
ming pool it must be realized that once the pool is 
painted there will be a continuous maintenance cost. 
Paint seldom can be expected to last more than 2 or 3 
years and in most cases pools are repainted every 
year. However, periodic painting adds materially to 
the attractiveness of the pool by keeping it looking 
fresh and clean. 

There are examples of both successful and unsuc- 
cessful use of practically all paints. The principal rea- 
son for poor results is improper preparation of the 
surface and improper application of the paint. The 
manufacturers recommendations should be carefully 
followed in all details. 

Regardless of the type of paint used, the surface of 
the pool must be clean and free from old paint which 
may scale. When portland cement paint is used, the 
surface must be damp when the paint is applied and 
must be kept damp for at least 2 days after painting 
so that the cement can hydrate. With other types of 
paint, the surface must be dry when the paint is ap- 
plied and the paint must be allowed to completely 
harden before the pool is filled. 

If colored cement plaster or concrete is used, only 
high-grade mineral colors should be considered*. 
Cheap colors will fade, and even with high-grade pig- 
ments it is difficult to obtain permanent color of certain 
shades. To obtain the desired color it may be necessary 
to use white portland cement and white or specially 


rough surface so that there will be a mechanical bond 
with the plaster. A satisfactory surface may be ob- 
tained by using rough form lumber, lining the forms 
with coarse burlap, or roughening with a heavy wire 
brush or scoring tool if the forms are removed early, 
generally within 24 hours. Oil or soap should not be 
used on the forms. The walls should be clean and 
damp when each coat of plaster is applied. The first 
coat should be dashed on the wall with a stiff brush, 
using a sharp whipping motion. Care must be exer- 
cised to insure a good bond and to eliminate the possi- 
bility of water getting between the concrete and the 
plaster. Other requirements are the same as for plas- 
tering or stuccoing on any concrete wall.* Adequate 
curing is very important. 

Cast stone—precast concrete slabs—may be used to 
form the entire thickness of the wall or to act as form- 
ing and facing for a cast-in-place concrete wall. In the 
former construction, a reinforced concrete frame is 
cast behind the precast slabs. In the latter construc- 
tion, the precast slabs are used as the front form and 
facing of an ordinary concrete wall. 

Colored tile, vitreous or glazed brick, or cast stone 
make attractive linings for swimming pools. The wall 
surface should be rough to aid in obtaining a good 
bond for the mortar in which these units are set. Care 
must be taken, particularly in outdoor pools, to pre- 
vent water from getting between the concrete and 
the lining. 


Winter Protection 


The best protection of outdoor swimming pools dur- 
ing the winter is a moot question, partly because 
winter damage to properly designed and constructed 
pools is so rare that no definite conclusions can be 
drawn as to the effectiveness of the various methods. 


In the past most pools were drained. A few of these 
had the bottom covered with straw, while others were 
completely covered with a roof. In some cases water is 
left in the pool throughout the winter. Of course, in all 
cases, pipes should be drained and equipment properly 
protected. 


*A dditional information is contained in Mineral Pigments for Use 
in Coloring Portland Cement Concrete and Plasterer’s Manual. 


selected colored aggregate as well as mineral colors. 
It will often be advantageous to use factory-mixed ce- 
ment and pigments, thus eliminating this work on the 
job and obtaining more uniform results. 

Much of the trouble with colored concrete has been 
that the desired color is obtained with the cement 
paste which covers the surface of the new work, but 
as soon as this wears off slightly the aggregate is ex- 
posed, thus changing the color effect considerably. To 
determine the final effect, a sample of the surface 
finished to be used may be rubbed or ground slightly 
to expose the aggregate. 

If the walls are to be plastered, they should have a 


The children’s pool at Westwood Common is one of many scattered 

over Cincinnati. Each pool has showers and a comfort station. The 

wide distribution of these small pools provides healthful recreation 
within walking distance for nearly all children. 


NS stars ag cet eesoneskassmam No: 


While the force exerted by the freezing of water in 
a closed receptacle is tremendous, the force exerted by 
the ice in a swimming pool does not seem to be danger- 
ous. Since the ice forms gradually and is free to expand 
in a vertical direction, it will buckle in the center of 
the pool as soon as horizontal pressure occurs due to 
freezing of a thin sheet. Owing to this progressive 
action and the fact that the volume of ice decreases 
as the temperature falls below the freezing point, the 
pressure developed on the walls is not dangerous. 

Another factor which reduces the effect of the lateral 
pressure from the ice is that the surrounding ground 
freezes at the same time, and consequently assists the 
walls in resisting any outward lateral force. 

Having the pool filled with water the year around 
will reduce the volume change in the concrete by prac- 
tically eliminating change in moisture content and re- 
ducing the maximum temperature variation to about 
50 degrees. Not only is the maximum temperature vari- 
ation reduced, but the number of cycles of high and 
low temperatures is very greatly reduced. 

The most important objection to leaving water in the 
pool during the winter is the possibility that the wall 
surface at the water line may be damaged by alternate 
freezing and thawing. 

Where water is left in the pool during the winter, 
all the pipes should be drained, and special equipment, 
such as lights, should be protected in accordance with 
the manufacturer's recommendations. The overflow 
drain should be left open so that no ice will form in 
the confined space of the overflow. Ordinarily, it is 
best to have the level of the water several inches below 
the overflow. However, if it is desired to flood the 
pool clear to the top, there should be no objection as 
long as the overflow gutter is very definitely below 
the surface so that any pressure exerted by ice in the 
overflow will be resisted by the ice from the outside. 

If the pool is drained for the winter, it is very im- 
portant that there be adequate subsurface drainage 
to prevent heaving of the floor slab caused by freezing. 

An unguarded swimming pool is a distinct accident 
hazard to both people and animals whether the pool 
be empty or full. This is particularly true in the winter 


16 


Walls of cinder concrete masonry and ceiling areas broken by 

reinforced concrete rigid frames reduce reverberation in the 

pool of the Iowa State Teachers College, Cedar Falls, Iowa. 

Concrete bleachers, separated from the pool, are easily kept 
clean. Keffer and Jones, architects. 


The graceful diving stand of reinforced concrete adds to the 
beauty of the pool setting at the Rockford, Illinois, Country 
Club. Mogens Ipsen, engineer. 


1 OR ee eR Re | 


when the pool may not be inspected for long periods. 
It is, therefore, advisable to have the pool enclosed 
the year around. Where a permanent fence is not used, 
a temporary fence may easily be erected by placing 
fixtures in the walks close to the pool for the insertion 
of steel posts. With small pools, particularly at country 
clubs, it is a simple task to insert these posts each 
night and attach one or two ropes to guard the pool 
when no one is in attendance. 


Lighting 


A good lighting system adds much to the attractive- 
ness of a pool and increases its hours of usefulness. 
Frequently a pool is used more in the evening than 
during the rest of the day. All pools used at night 
should have the entire pool enclosure well lighted. In 
addition to the required overhead lights for general 
illumination, underwater lights add appreciably to the 
attractiveness and safety of the pool. 

There are several types of both overhead and under- 
water lights. The selection of the best types and their 
location to give the correct illumination at all points 
requires the services of a lighting specialist. Overhead 
lights should not be placed close to the pool since 
they attract bugs which would fall into the pool and 
onto the walks. 


Underwater lights should be installed so that they 
may be serviced without emptying the pool. 


Indoor Pools 


It has been quite common practice to locate indoor 
pools in the basement because of saving in construc- 
tion costs, even though it was more desirable to have 
them in the top story where windows and skylights al- 
lowed better ventilation and an abundance of sunlight. 
These latter considerations have lost much of their im- 
portance with increased use of mechanical ventilation 
and development of lamps with therapeutic properties. 

Two of the biggest problems in connection with in- 
door pools are condensation and acoustics. The air in 
the room has a high moisture content which will cause 
condensation on walls and ceiling having a lower tem- 
perature. This trouble may be minimized by adequate 
ventilation and insulation of walls and ceiling. Fairly 
rapid changes of air will reduce the moisture content. 
The temperature differential between air, walls and 
ceiling may be reduced by keeping the room tem- 
perature as low as possible without discomfort to the 
bathers and by insulating the walls and ceiling, par- 
ticularly exterior walls and roofs. 

Most rooms for indoor pools are notoriously bad 
acoustically, since practically all ordinary room sur- 
faces and equipment are highly sound reflective. It is, 
therefore, advisable to reduce the sound reflection 
from the walls and ceiling as much as possible by 
using sound-absorbing material. Breaking up the ceil- 
ing area with beams will also reduce reverberation. 


, combination of underwater and overhead lights makes the 
»00l at Shawnee, Oklahoma, safe and attractive at night. C. E. 
Edge, engineer. 


}eparation of diving, swimming and wading areas is desirable 
or safety. Cazenovia Park, Buffalo, has three pools completely 
eparated by fencing. Placing the ladders across the pool from 
he diving boards practically eliminates diving accidents and 
decreases time between dives. Roeder J. Kinkel, architect. 


Except with the best ventilation, temperature con- 
trol and insulation, there will probably be some con- 
densation. Unfortunately, most acoustical materials 
are affected by moisture so that great care must be 
taken in selecting them. Precast concrete units made 
with lightweight aggregates have considerable sound- 
absorbing value and will not deteriorate but rather 
grow stronger in the presence of moisture. Any color 
scheme may be obtained by painting with portland 
cement paint, and acoustical properties will not be 
materially reduced. Interesting architectural effects 
may be obtained by use of different-sized units. It is 
generally advisable to sacrifice acoustical properties on 
the walls for a height of 5 or 6 ft. and to use a smooth 
finish such as cast stone, glazed tile or enamel, which 
will not be affected by body contact. 

Because of the noise and difficult acoustical condi- 
tions, swimming coaches have found microphones and 
loud speakers of considerable assistance. 

Lighting of indoor pools should be arranged to 
eliminate glare. Underwater lights may be used here 
as well as in outdoor pools, although the greater in- 
tensity of general illumination reduces their advantage. 

The minimum ceiling height will be governed by the 
diving equipment contemplated. There should be no 
obstructions within a radius of about 13 ft. from the 
end of the springboard. 


Sanitation 


The construction and operation of a modern swim- 
ming pool is a sanitary engineering problem. The de- 
sign and equipment should be, and in many states 
must be, approved by the local and state health 
officials before construction is started. 

From the standpoint of water supply, there are 
three general classifications of pools: fill-and-draw, 
flow-through, and recirculation. 

In the old “fill-and-draw” system, the pool is com- 
pletely emptied and refilled with fresh water at inter- 
vals. Between refillings the water may be intermittent- 
ly disinfected and chemically corrected. A commercial 
sodium hypochlorite solution is most commonly used 
for this purpose. This system is not recommended for 
public pools and most health authorities will not per- 
mit its use in new pools. The cost of the fresh water 
for refilling is usually considerably more than the cost 
of recirculation. Heating the fresh supply to a satis- 
factory temperature for bathing, particularly in the 


spring and fall, is also an item of considerable expense. 
In addition the pool will be out of service a consider- 
able portion of the time while water is being changed. 

With the “flow-through” system, there is a con- 
tinuous flow of fresh water into the pool and a cor- 
responding overflow. It is wise and sometimes neces- 
sary to add a chemical which will provide an adequate 
residual disinfectant. This system may be used satis- 
factorily where there is an adequate natural flow of 
pure water. Even where the water must be pumped, 
this system may be economical for private or semi- 
private pools where the discharged water can be used 
for other purposes such as watering lawns. The tem- 
perature cannot be readily controlled. 

Most of the pools built today use the recirculation 
system in which water is continuously drawn from the 
pool, passed through filters and other purification 
equipment, and then returned to the pool. This system 
requires only sufficient fresh water to make up for that 
lost by evaporation and through the overflows where 
the latter drain to the sewer. A minimum of heat is 
required to keep the water at the proper temperature. 
In fact, after outdoor pools have reached the proper 
temperature, there is more difficulty in keeping the 
water cool than in keeping it warm. 

In recirculation pools the water usually enters 
through inlets near the top of the walls and is with- 
drawn through one or more outlets at the deepest 
point in the pool. The Joint Committee recommends 
that the inlets in rectangular pools be placed across 
the shallow end so that each inlet serves not more 
than 15 ft. of width. For all except the smallest pools, 
it is advisable to have a small amount of water enter 
at the deep end also. For pools exceeding about 35x75, 
it is desirable to have inlets on the sides as well as the 
ends. For large pools with outlets at the center, inlets 
should be placed around the entire perimeter. Where 
a rectangular pool without a hopper bottom is more 
than 20 ft. wide, multiple outlets should be provided, 
spaced not more than 20 ft. apart. They should be 
covered with a grating and the area should be sufficient 
to reduce the suction to a safe point. The inlets and 
outlets should be so arranged that all the water will 
be moving and there will be no “dead spots”. 

The so-called “closed system” is now gaining favor 
in certain parts of the country. In this system, drainage 
through the overflow is returned to the filter. In many 
of these pools the discharge from the main drain is 
controlled so that there is a considerable overflow 
which removes surface dirt and keeps overflows clean. 

In still another new system, sometimes called the 
“reverse flow”, the water enters at the bottom of the 
pool and is all drawn off through the overflows. 

Filtration removes from the water all suspended 
matter and a portion of the bacteria. There are several 
types of filters in use for the purification of water in 
swimming pools. The most common is the pressure 
filter, which occupies a comparatively small space, is 
relatively simple to operate, and gives excellent results. 

The diatomaceous earth type of filter so widely used 


18 


Diving towers such as these at Astoria Park are used by 
the New York City Department of Parks. 


by our armed forces is becoming popular for swimming 
pools. It is compact, easy to operate and relatively low 
in cost. 

The gravity sand filter, used in many water supply 
systems, is also frequently used for swimming pools. 
When properly designed, this type of filter is efficient, 
easy to operate, and economical in construction, par- 
ticularly for large pools. 

Most health authorities recommend that the pumps 
and filters be large enough to recirculate the entire 
content of the pool in 8 hours or less. 

The filtration process returns the water to the pool 
in a clear, sparkling condition, free from turbidity 
and suspended matter, as well as a portion of the 
original bacteria content. In order to have a water 
free from all disease-producing bacteria, a germicidal 
treatment of the water is necessary in addition to fil- 
tration. Several disinfecting agents have been used, 
including chlorine, bromine, ultra-violet light, ozone, 
and colloidal silver. 

At present chlorine is used almost exclusively but 
the use of bromine is increasing. Chlorine may be used 
in the form of gas compressed to a liquid, sodium 
hypochlorite or calcium hypochlorite. Sodium hypo- 
chlorite may be formed at the pool by electrolysis of a 
solution of common salt. The use of ammonia with 
chlorine has some benefits. Adding chlorine before 
filtration will require the use of a slightly greater 
amount, but will aid in keeping the filters in good 
condition and prevent growth of bacteria on them. 

Algae, which form either a greenish or brownish 
cloud in the water or form a slippery coating on walls 
or floors, often appear in outdoor pools. Maintenance 
of the standard chlorine residual will assist greatly in 
preventing algae. Energetic control measures should 
be undertaken immediately upon the first signs of 
algae. Treatment with copper sulphate is the most 


common method, but other forms of copper, par- 
ticularly colloidal copper, are being used. Super- 
chlorination is rapidly gaining favor as a control 
for algae. With this treatment a large excess of chlorine 
is added when the pool closes at night. The next day 
the excess will have been dissipated so that the pool 
can be used. 

The amount of copper sulphate required will vary 
greatly, depending upon many things including the 
type of algae and the water purification system. Ordi- 

narily about 5 to 20 lb. per 1,000,000 gal. will be 

satisfactory. In severe cases it may be necessary to 
drain the pool and scrub walls, floor and walks with 
strong copper sulphate or deahidi hypochlorite solu- 
tion. 

The copper sulphate may be applied through a treat- 
ment tank, by dragging through the water a sack or 
perforated can filled with crystals, or by sprinkling a 
strong solution over the top of the water and then 
agitating it violently. 

“Athlete’s foot”, a fungus growth similar to ring- 
worm, is now receiving serious attention at all well- 
operated swimming pools. Every precaution should be 
taken to prevent its spread. The floors of the bath- 
house and the pool walks should be washed and dis- 
infected at least once daily. It is frequently required 
that foot baths containing a fungicidal solution be so 
placed that bathers must walk through them in going 
to and from the pool, but their effectiveness is open 
to serious question. 

Every pool should have a suction cleaner as part 
of its equipment. Regardless of the efficiency of the 
water purification system and pool operation, dirt will 
accumulate on the bottom of the pool. The only satis- 
factory way of removing this is with a suction cleaner. 
There are several types which work satisfactorily. 
Some have permanent connections spaced around the 
pool to which the suction hose and cleaner may be 
attached as needed, the suction being obtained from 
the main water return line or from a special pump. 
Another type has a portable self-priming suction pump 
which may be pulled around the edge of the pool. 


An example of the 
simple private pool 
is this one at the 
home of Seton I. 
Miller, Van Nuys, 
California. Charles 
O. Matcham and 
PauLO. Davis, archi- 
tects. 


A very important piece of operating equipment 
which is sometimes overlooked is the hair and lint 
catcher, which should be installed in the suction line 
of all recirculating systems. It will remove hair, lint 
and other small solid wastes from the water and thus 
protect the pumps and filters. The hair catcher must 
be readily accessible and it is advisable to use one 
which is extra large and easily changed. 

Water and sewer connections must be so made that 
there is no possiblity of reverse flow from the pool to 
the water supply system or from the sewer to the pool. 
Most state health departments require a broken con- 
nection between the original water supply and the re- 
circulating system, accomplished by using an open 
surge tank with the original water outlet at least 6 in. 
above the tank. The new water should pass through 
the filter before entering the pool so that any sus- 
pended matter will be removed. 


Amusement Equipment 


Pool equipment may include springboards, diving 
towers, chutes and floats. Safety should be the most 
important consideration in both the selection and in- 
stallation of equipment. 

Many bathers, more interested in diving than swim- 
ming, are attracted to the swimming pool by the 
springboards and diving platforms. A standard diving 
board will be found more satisfactory and economical 
than a makeshift board. Furthermore, if diving con- 
tests are held under standard regulations, the board 
must be constructed and installed in accordance with 
the specifications of the National Collegiate Athletic 
Association and the Amateur Athletic Union. 

Diving platforms placed at the regulation heights, 
provided a sufficient depth of water is available, will 
be very popular among the better divers. 

Springboards and diving platforms should be coy- 
ered with cocoa fiber matting to prevent slipping. This 
material, being loosely woven, dries out quickly and 
thus preserves the board. If spare boards are kept on 
hand, they may be changed from time to time, per- 


This development at Mar- 
shall, Missouri, includes an 
architectural concrete bath- 
house, swimming and diving 
pool, wading pool and sand 
beach. Note the shower be- 
tween the sand beach and 


mitting them to be refinished and covered, which will 
greatly prolong their usefulness. 


Chutes or slides, properly constructed, are quite safe 
and furnish a real thrill. In small pools they are im- 
practical, but where there is sufficient space they con- 


tribute greatly to the popularity of the pool. 


The greater part of time spent in the water is de- 
voted to play rather than to actual swimming, so that 
play equipment, such as floats, inflated rubber horses, 
frogs, and fish, will be found very useful and com- 
paratively inexpensive. 


SPECTATOR FACILITIES 


The financial success of a pool depends upon public 
interest which will create patronage. Interest may be 
greatly enhanced by adequate provisions for spec- 
tators, for whom separate seating and toilet facilities 
should be provided. The latter can be located in the 
bathhouse but should be so arranged that the spec- 
tators and bathers are completely separated at all 
times. 

Where funds are available, it is wise to build per- 
manent spectator galleries or bleachers which require 
no upkeep other than sweeping or flushing with a hose. 
The actual seats may be anything from the plain 
board seats of the usual bleachers to movable chairs. 
The seats should be on the west or south side of the 
pool so that the spectators will not face the sun and 
should preferably be parallel to the diving boards. 
Where the bathhouse has a flat roof, provision can 
easily be made for using this space for spectators. 


Many pools obtain additional direct revenue by 
charging a nominal admission to the spectators’ gallery. 


BATHHOUSES 


The bathhouse is an integral and important part of 
the outdoor swimming pool and should be designed to 


20 


Perkins, architect. 


harmonize with the pool and its surroundings. 

The first impression a patron receives_as he arrives 
and the last impression he has as he leaves is of the 
bathhouse, so it is very important that the bathhouse 
have the same atmosphere of cleanliness and sanitation 
as is built into the pool. 

Location of the bathhouse with reference to the pool 
will depend upon the size of the pool and the space 
available. However, when possible, they should be 
arranged so that the bathhouse will protect the pool 
from the prevailing winds. It should be placed along 
the side of the pool or preferably at the shallow end 
in order to reduce the danger of poor swimmers and 
children jumping into the deep water. 

The capacity and operation of the bathhouse must 
be such as to avoid overcrowding at times of maximum 
demand. However, as with the pool itself, it is better 
to have an overcrowded condition a few times a year 
than to have facilities so large as to be uneconomical 
most of the time. 


Size and Equipment 


Some of the many factors affecting the size of the 
bathhouse in relation to the size of pool are: lockers 
or central checking system; individual dressing rooms 
or dormitory system; private or group showers; and 
extra facilities. If privately-owned suits are allowed, 
some patrons will come to the pool all ready to swim, 
so that the size of dressing and check rooms may be 
reduced; but since all bathers should be required to 
take a cleansing shower, the number of showers should 
remain the same. 

An investigation of several pools shows that the area 
of the bathhouse averages about one-third the area of 
the pool, which is fairly comparable to the suggestion 
that the area of dressing rooms be about one-fifth the 
area of the pool. 

The Joint Committee recommends bathhouse facili- 
ties be provided as shown below, based on the number 


the swimming pool. R. N. 


of bathers present at any one time, two-thirds of whom 
may be assumed to be men: 

1 shower for each 40 bathers. 

1 lavatory for each 60 bathers. 

1 toilet for each 40 women. 

1 toilet for each 60 men. 

1 urinal for each 60 men. 


Arrangement 


Very often the financial success of a pool depends 
upon the arrangement of the bathhouse. The entire 
project should be so planned that the pool and bath- 
house can be operated with a minimum personnel, 
particularly during slack periods. 

Manager's office, first aid room, cashier, suit and 
towel rooms, and check room for valuables should be 
in the center of the building. The wings at either end 
of the building may house lockers, dressing rooms, 
toilets and showers, those for men being located on 
one side and those for women on the opposite side of 
the lobby. 

All facilities should be so arranged that patrons can 
pass through quickly without confusion. The only 
route from the dressing room to the pool should be 
past the toilet and shower rooms. Each patron should 
be required to take a thorough cleansing shower with 
soap before putting on a bathing suit. An adequate 
supply of warm water must be provided. By requiring 
each bather to pass through a group of showers before 
entering the pool, at least a superficial bath will be ob- 
tained but this should not be considered as replacing 
the required shower in the nude. 

It is desirable for bathers returning from the pool to 
pass through a separate drying room to the dressing 


Men's Dressing Room 


Phone 


FLOOR PLAN 


room, and for the “wet” and “dry” bathers to be 
separated as much as practicable. The exit from 
the bathhouse to the street should be so arranged 
that an attendant may collect all keys, checks, suits 
or other supplies belonging to the establishment. 

Toilets should be accessible directly from both the 
dressing room and pool. Separate ones for wet and dry 
bathers are very desirable. The wall-hung prison type 
of fixtures are the best. Disinfecting foot baths should 
be placed between the pool and the toilet. 

Floors of bathhouses should be pitched about 14 in. 
per ft. to frequent outlets to assure rapid drainage. 
There should be an ample number of hose connections 
to make cleaning easy. Not less than 1-in. hose should 
be used so that there will be adequate water volume 
and pressure. 


Dressing Room Facilities 


The method of clothes checking must be determined 
before the bathhouse layout can be made, as the 
method will vitally affect the entire arrangement. 

Both individual lockers and baskets or bags checked 
in a central room have been used successfully for the 
storage of clothing, the choice between the two de- 
pending mainly upon local conditons. A combination 
of the two systems is possibly the most desirable since 
obviously the requirements for a well-dressed adult 
and a boy in play clothes are not the same. Lockers 
should be placed on a raised platform to keep them 
dry and to simplify cleaning the floor. Lockers are 
more costly and require more space, but tend to keep 
the clothes in better conditon. 

Some individual dressing rooms are generally pro- 
vided for women and girls. Men and boys will usually 


Lifeguard 
& Utility 


Phone} 


Suggested layout for a bathhouse with a capacity of 340 persons corresponding to a 40 x 100-ft. pool. 


21 


This architectural concrete bathhouse at | 
Kearney, Nebraska, forms an integral part 
of the pool development. A fence separates 
wading and swimming areas. McClure and 
Walker, architects. 


dress in the aisles between rows of benches or lockers. 
A few individual dressing rooms are sometimes pro- 
vided in the men’s section. 

Regardless of the system adopted, dressing and 
locker rooms should be arranged to permit a maximum 
of sunlight and air. A bright, airy dressing room will 
do much toward maintaining it in a clean, sanitary 
condition. 

Both individually and group-controlled showers are 
in general use. Control and operation of each group 
vary and all have advantages and disadvantages. How- 
ever, all modern equipment has some type of control 
so that there is no possiblity of bathers being scalded. 

There are many kinds of bathhouse equipment on 
the market which add to the convenience of the pa- 
trons and increase the popularity of the pool. The hair 
dryer is practically a necessity for the women bathers. 
Comb-vending machines, exercisers and scales are fre- 
quently installed by the most up-to-date pool oper- 
ators. 


Construction 


The particular use of the bathhouse requires con- 
sideration of special properties as well as the usual 


22 


a nmonscreret® 


‘. 
f 


The simple, clean lines of this archi- 

tectural concrete bathhouse at Du- 

buque, Iowa advertise the cleanliness 

of the swimming pool. C.I. Krajewski, 
architect. 


ones in the selection of construction materials. Some 
of the principal considerations are: architectural effect, 
cost, resistance to deterioration and fire, ease and cost 
of maintenance, and water resistance. 

The bathhouse, being an integral part of the pool 
development, should harmonize architecturally with 
the pool. It should give the impression of cleanliness, 
safety and happiness. 

Resistance to deterioration and fire is especially 
important in bathhouses. The dampness always pre- 
vailing is particularly harmful to some materials and 
causes rapid deterioration. Materials which are entirely 
satisfactory in ordinary buildings cannot be used 
for bathhouses. Durng a considerable portion of the 
year, the bathhouse is without attendants and is gen- 
erally in an isolated location and thus subject to 
vandals. A fire starting under such conditions could 
gain considerable headway before detection. 

Bathhouses must be kept scrupulously clean. The 
easiest and most satisfactory way of doing this is by 
frequent washing. The construction should be such 
that washing may be done with a high-pressure hose 
without damage to the building. 

Architectural concrete meets all these requirements 
admirably. Being of the same material as the pool, it 


gives the natural impression of being part of the de- 
velopment. Its clear-cut lines symbolize cleanliness, 
strength and safety. The inside may be left exposed 
without any treatment except possibly painting. This 
reduces the original cost, the possibility of deteriora- 
tion from any cause and makes the building easy to 
clean with a hose. Such a structure is highly fire- 
resistant and vandals can do little damage to it. 

Hollow concrete masonry units* also are an admir- 
able material for bathhouses. The walls may be simply 
painted or may be covered with portland cement 
stucco* on the outside and portland cement plaster on 
the inside. When the units are laid in a random ashlar 
pattern, patricularly interesting architectural effects 
may be obtained. Here again the material is economi- 
cal in first cost, is very resistant to deterioration and 
fire, is easy and economical to maintain, and is not 
affected by moisture. In addition, the units made with 
lightweight aggregates have good acoustical proper- 
ties. 

Quite satisfactory results have been obtained from 
the open court type of bathhouse in which the roof is 
omitted over part of the dressing room area. The 
abundance of sunshine and air thus admitted to the 
dressing areas helps to keep them in a sanitary condi- 
tion. There is also some saving in original cost. 


Equipment Room 


The room for mechanical equipment must be of 
adequate size to permit easy access to all equipment 
both for usual operation and for necessary repairs. 
There should be easy access to the room to encourage 
rather than discourage frequent attention to equip- 
ment. Adequate ventilation is important to prevent 
deterioration of equipment. Floors should be pitched 
about 14 in. per ft. to frequent drains or to gutters. 


*Additional information is contained in Concrete Masonry 
Handbook and Plasterer’s Manual. 


OPERATION 


A swimming pool must be intelligently operated to 
be a success. This requires not only an efficient and 
dynamic manager, but also an intelligent, trained per- 
sonnel, At least one lifeguard should be at the side of 
the pool at all times when swimming is permitted. 
This lifeguard should be not only an expert swimmer, 
but should also be trained in lifesaving, resuscitation 
and first aid. Lifesaving and first aid equipment should 
always be available. Attendants should wear uniforms 
or some identification indicating their authority to 
enforce rules. 

The public demands and will pay for good service. 
All employes should understand this. The arrange- 
ment of the pool and bathhouse and the selection and 
training of the personnel should be such that the oper- 
ation is flexible enough to manage the pool efficiently 
with a small force during slack periods and a larger 
force during rush periods. The bathers should be un- 
der supervision from the time they buy their ticket 
until they leave the premises. 

Regulations are necessary to insure sanitary condi- 
tions and to maintain order, but they should be as 
few and simple as required to obtain the desired re- 
sults. Once regulations are established they should be 
quietly but strictly enforced. Posting these rules in 
conspicuous and appropriate places will aid in their 
enforcement. The posters should contain headline 
phrases in large letters. Using a series of educational 
posters will help materially in gaining the patrons’ co- 
operation in the enforcement of the rules. 

The smart operator recognizes the importance of 
perfect cleanliness, both real and apparent. Because 
light-colored materials show dirt easily, they force the 
operator to keep them clean, and they impress the 


public with the cleanliness of the establishment. Each 
morning the suction cleaner should be used to remove 
any dirt from the bottom of the pool, and any floating 


At Crotona Park, New 
York City, one attend- 
ant can handle 
clothes checking and 
closely supervise 
dressing room during 
slack periods, while 
additional attendants 
can work efficiently 
during rush periods. 
Designed by Depart- 
ment of Parks. 


/ | 
a9 j 20 
2 o"| . 30-0 A ne ake : 
| N 
i a Inlet or 2 if 
ill ‘x of fountain ° 
~ 


| 
| 
| 
| 
| 
| 
Overflow —, LL 


aA Ti \ Ia im 
Li | 
1.0 
\ | 
‘\ 
rae = =e = === -- : 
2" Inlet 
6"Drain SE 
PLAN Pitch ‘ per ft. 
6'2:0"_ Water level 30:0" to =e | 


Drain tile - bottom half 
of joints cemented,top 
half covered with roofing 
paper 


20x 24" - 
Removable ~ pica ; 
La Vise ROO OPN , “yl ek 
5 " mech oe Bair j i 7 
{ \ Pitch drain nee 
ie 4" per ft. cod 
[fe removed OVERFLOW 
in winter 
SAND TRAP 
Sugge 


debris should be removed by skimming or overflowing 
The walks and the floors of the bathhouse should also 
be washed daily and waste paper and rubbish col- 
lected as frequently as necessary during the day. 

All mechanical equipment requires some attention. 
The manufacturers give instructions for the proper 
operation of their equipment. The instructions should 
be posted near the equipment and carefully followed. 
All equipment should be thoroughly checked enough 
in advance of the opening of the season to have any 
necessary repairs made. 

Expansion joints must be renewed occasionally. 
They should all be carefully inspected before the sea- 
son opens, and new material added where required. It 
will sometimes be necessary to remove the old material 
and completely replace it. 

One of the important jobs of the manager of a 
successful pool is to create and maintain interest in 
swimming. This may be done in several ways, includ- 
ing sponsoring “learn to swim” campaigns, instruction 
in lifesaving, competitive games and exhibitions. 


REVENUE 


When studying operating expenses and incomes 
from swimming pools, consideration must be given to 


24 


ested designs for wading pools. 


Lars 
7 oe Drain tile 


Walk drains 


Pitch to drains 
%" per ft. 


MUS etre = - = Sects a OTE z ——— POTEET at | ae 
4 j Spasrag ttsene ie 

ohn’ 6"Sand joann swiaia| | fiseacansenser * Een S 4d 

A Sand tap aa Drain tile-bottom half 

of joints cemented ,top 

half covered with 

roofing paper 


Extra bars at a 
inlet oot a Cross SECTION 


Mastic 8" 
Walk drai nr\\o 


Water level 
6", --Mesh or bars 


-20"% CBU 2 


% wie UNDA Ribsit. Wh 
Zs 


Be a Sone Perret 
Gea tile 


Watt SECTION 


RIL 


6'Pipe; 


cP ASOr4awas/] 9 
“M5 Oc 


tb ILA 
Plug removed Axe h 


in winter—~ Ci 4" ie] 
SAND TRAP 


the purpose for which the pool is operated. Many 
pools, the same as other park facilities, are operated 
primarily as a health and recreational service to the 
community. While there are some pools which are en- 
tirely free to the public, a charge is made for the use 
of most of them. These charges are established to pay 
part of the expense, to pay the entire expense or to 
make a profit. 

In determining the charges, special consideration 
should always be given to the children. Interesting 
them in swimming will increase general interest in the 
pool and will also build future patronage. During the 
morning, at least, children should be admitted free 
or for a very nominal fee. 

For public pools admission charges vary from 
nothing to $1 for adults, and from nothing to 50c for 
children, but the common range is from 25c to 50c 
for adults and 10c to 25c for children, with special 
rates for children during certain hours. Season tickets 
vary from 10 to 30 times the cost of a single admission, 
20 times being most common. At some pools, season 
tickets for the entire family are available at only a 
slight increase over the cost of individual season 
tickets. 

The financial success of a pool depends in a large 
part upon the standards and methods of operation. 


WADING POOLS 


Some outdoor public swimming pools are designed 
with a section to be used as a wading pool. However, 
the depth of water at the shallow end of such pools is 
often greater than is safe for small children unable to 
swim. Even when the shallow end is such as to be 
satisfactory for wading, there is always possible danger 
of small children venturing too far into deep water, 
where they are soon in trouble unless help comes 
quickly. The occasional contamination, unavoidable 
with small children, is very undesirable in the main 
pool. For these reasons, wading pools should be 
made as independent structures. Where constructed 
as part of the swimming pool, the wading area, includ- 
ing walks, should be set apart by a fence. 


Two or more small pools are much better than one 
large pool. If the small pools can be located in different 
parts of the city, it is still better. Small areas not suit- 
able for swimming pools can often be utilized for wad- 
ing pools. School “grounds and small city playgrounds 
as nerell as public parks may be used. Wading pools do 
not require bathhouses. 


The floor of the pool may slope gradually to above 
the water line or may have a low curb around it, giving 
a water depth of about 6 in. The maximum depth 
should not be more than about 24 in. The bottom 
slope must be very gradual, not more than 1 to 15. 


With wading pools, the quantity of water is small, 
the contamination high and a considerable amount of 
sand and debris is carried into the pool so that it is 
not advisable to recirculate the water. The fill-and- 
draw system is frequently used, but the flow-through 
system is preferable, particularly where the load is 
heavy. Even with the flow-through system it is advis- 
able to drain and clean the pool each night. Because 
of the large amount of sand and other debris carried 
into a wading pool, it is necessary to provide simple, 
accessible sand traps in the drainage system. 


Showers or fountain sprays are always enjoyed by 
the children and may be used as the water inlet. Some 
health authorities are strongly urging that fountain 
sprays be used without retaining an appreciable 
amount of water in the pool. 


A sand play beach is a big addition to a wading pool. 
However, the sand must be frequently scr eened to its 
entire depth and thoroughly disinfected. Several times 
a day it should be raked and sprinkled with a dis- 
infectant. A concrete slab provided with frequent 
drains, underlying the sand, will aid materially in 
keeping the sand in a sanitary condition. 


Even as simple construction as a dished concrete slab with flush 

lawn sprinklers will provide great enjoyment for the children. 

The sprays can be manually operated for short periods as the 
demand requires. 


hee Dy fe Rd IRIE N 
i (F we oP SOE: 
€.° Wet Hoe 3 <a}  @ 6's d Ze, LAS 
oh es — aw | an or 5 Ce 
ae 6"Tile aes gravel fill vee 


Cross SECTION 


Suggested design of spray pool. 


25 


CONCRETE SPECIFICATIONS FOR SWIMMING POOLS 


1. Portland Cement 


Portland cement shall comply with the ‘‘Specifications for 
Portland Cement,” ASTM Designation: C-150*; the “‘Specifica- 
tions for Air-Entraining Portland Cement,’’ ASTM Designation: 
C-175; the “‘Specifications for Portland Blast-Furnace Slag 
Cement, ASTM Designation: C-205; or the “Specifications for 
Portland-Pozzolan Cement,” ASTM Designation: C-340; and 
shall be Typesee. eased. she 


** Insert one of the following: 
Type I, IA, IS, ISA, IP or IPA for use in general concrete construction 
when the special properties of the other types are not required. 


Type II or ILA}—for use in general concrete construction exposed to moderate 
sulfate action or where moderate heat of hydration is required. 


Type ITI or IITA+—for use when high-early-strength is required. 


+Nole: “A” after the type number designates air-entraining portland cement. 
Air-entrained concrete, obtained by use of an air-entraining portland cement or 
by an air-entraining agent added at the mixer, is recommended where severe frost 
action prevails. 


2. Fine Aggregate 
Fine aggregate shall consist of sand having clean, hard, du- 
rable, uncoated grains, free from deleterious substances. 


Fine aggregate shall range in size from fine to coarse within 
the following percentages by weight: 


PassinosINonmr Aisle vie sean arene 95 to 100 per cent 
Passing JNO. LOjsie Viera eee ee ree 45 to 70 per cent 
PassingNoavo0 sieve. a ee senor 15 to 30 per cent 
PascingwN ol OO:sievicrs ti art einen: 3to 8 per cent 


Volume removed by sedimentation. . Not more than 3 per cent 


3. Coarse Aggregate 


Coarse aggregate shall consist of crushed stone, gravel, or other 
approved inert materials with similar characteristics or combina- 
tions thereof, having clean, hard, durable, uncoated particles, free 
from deleterious matter. 

Coarse aggregate shall range in size from fine to coarse within 
the following percentages by weight: 


Passings 2-1 sley Cae ee eee ee 95 to 100 per cent 
Passing' 127 -1n-(sievGse on aes eet aie: 35 to 70 per cent 
PERS CBSE SEO. oh y oon mooremoannar 10 to 30 per cent 
Passing JNosAisiey Ca acre een een 0 to 5 per cent 


Bank or pit-run aggregate in its original state shall not be used. 


4. Mixing Water 


Mixing water shall be free from oil, acid, and injurious amounts 
of vegetable matter, alkalies or other salts. 


5. Reinforcement 

Reinforcement shall conform to the American Society for Test- 
ing Materials specifications for reinforcement bars of intermediate 
grade billet or axle steel or rail steel or for cold drawn wire. 


6. Measuring Ingredients 

Aggregates shall be measured separately by weight or volume. 
Water shall be so measured as to insure the desired quantity in 
successive batches. 


7. Water-Cement Ratio 


The proportioning of materials shall be based on the require- 
ments of a workable mix containing not more than 6 gal. of 
water per sack (94 lb.) of cement. This quantity of water must 
not be exceeded. Water in the aggregate must be included in 
quantity specified and subtracted from amount added to mix. 


8. Moisture in Aggregate 


Moisture in the aggregate shall be measured by methods satis- 
factory to the engineer which will give results within 1 lb. for 
each 100 lb. of aggregate. 


26 


9. Workability 


The mixture shall produce concrete that can be worked readily 
into corners and angles of the forms and around the reinforcement 
without excessive spading or separation of materials. 

In no case shall more than 1 part of fine aggregate be used to 
1 part of coarse aggregate nor shall the amount of coarse aggregate 
be such as to produce harshness in placing or honeycombing. 


10. Trial Batches 


Full-sized trial batches shall be made in the mixer, using the 
aggregates selected for the job to establish the correct proportions 
to give proper workability with the water-cement ratio specified tf. 
The combination of fine and coarse aggregates shall be adjusted 
within limits specified until mix meets approval of the engineer. 


ll. Mixing 

Concrete shall be mixed in a batch mixer until there is a uniform 
distribution of materials. The entire contents of the drum shall be 
discharged before recharging. The volume of the mixed material 
per batch shall not exceed the manufacturer’s rated capacity of 
the mixer. The mixer shall be operated at the speed recommended 
by the manufacturer. Mixing of each batch shall continue not less 
than 1 minute after all materials, including water, are in mixer. 


12. Retempering 

Retempering of concrete which has partially hardened, that is, 
remixing with or without additional cement, aggregate, or water, 
will not be permitted. 


13. Depositing 

Before depositing any concrete, all debris shall be removed 
from the space to be occupied by the concrete, all steel reinforce- 
ment shall be secured in its proper location, all forms shall be 
thoroughly wetted (except in freezing weather) or oiled, and all 
formwork and steel reinforcement shall be inspected and approved 
by the engineer. 

Concrete shall be handled from the mixer to the place of final 
deposit by methods which shall prevent the separation or loss of 
ingredients and shall be deposited as nearly as practicable in its 
final position to avoid rehandling. It shall be deposited so as to 
maintain, until the completion of the unit, a workable surface 
approximately horizontal. The concrete shall be placed in a 
manner that will avoid accumulation of hardened concrete on the 
forms or reinforcement. Under no circumstances shall concrete 
that has partially hardened be deposited in the work. 


14. Depositing Against Other Concrete 


Before depositing new concrete on or against concrete that has 
hardened, forms shall be retightened, surface of the hardened 
concrete roughened as required, thoroughly cleaned of foreign 
matter and laitance, and moistened with water. The cleaned and 
moistened surface, including vertical and inclined surfaces, shall 
be slushed with a coating of neat portland cement grout against 
which the new concrete shall be placed before the grout has 
attained its initial set. Concrete for the first 6 in. of the new layer 
shall consist of a mix having one-half the amount of coarse aggre- 
gate in the regular mix. 


15. Compacting 


Concrete during and immediately after depositing shall be 
thoroughly compacted by means of suitable tools and shall be 
thoroughly worked around the reinforcement and embedded fix- 
tures and into corners of the forms. 

*Where reference is made to A.S.T.M. standards and the year of adoption is 
not shown, the current standard shall apply. 


+TWith average materials the first trial may be a mix of about 200-225 lb. 
of sand and 300-350 lb. of coarse aggregate per sack of cement. 


16. Protecting and Curing 


Exposed surfaces of concrete shall be protected from premature 
drying by methods approved by the engineer. All concrete shall 
be kept wet for not less than 7 days, except that 3 days shall be 
considered sufficient if high early strength portland cement or 
concrete is used. 


17. Temperature 


Concrete when deposited shall have a temperature not below 
70 deg. F. and not above 80 deg. F. In freezing weather, suitable 
means shall be provided for maintaining the concrete at a tem- 
perature not lower than 70 deg. F. for 3 days or 50 deg. F. for 
5 days after placing, except when high early strength portland 
cement or concrete is used the temperature shall be maintained 
not lower than 70 deg. F. for 2 days or 50 deg. F. for 3 days. The 
methods of heating materials and protecting concrete shall be 
approved by the engineer. Salt, chemicals or other foreign 
materials shall not be mixed with the concrete for the purpose 
of preventing freezing. 


18. Patching 


After removing forms and before the concrete is thoroughly 
dry, any poor joints, voids, stone pockets or other defective 
areas and all tie holes shall be patched. Defective areas shall be 
chipped away to a depth of not less than 1 in. with the edges 
perpendicular to the surface. The area to be patched and a space 
at least 6 in. wide entirely surrounding it shall be wetted to 
prevent absorption of water from the patching mortar. The 
patch shall be made of the same materials and proportions as 
used for the concrete, except that the coarse aggregate shall be 
omitted and white portland cement substituted for a part of the 
grey portland cement to match the color of the surrounding 
concrete. The amount of mixing water shali be as little as con- 
sistent with the requirements of handling and placing. The mortar 
shall be retempered without the addition of water by allowing it 
to stand for 1 hour, during which time it shall be mixed with a 
trowel to prevent setting. 

The mortar shall be thoroughly compacted into place and 
screeded, leaving the patch slightly higher than the surrounding 
surface. After being undisturbed for 1 to 2 hours to permit 
initial shrinkage, the patch shall be finished to match the ad- 
joining surface. 

Tie holes left by withdrawal of rods or the holes left by re- 
moval of ends of ties shall be filled solid with mortar. For holes 
passing entirely through the wall, a plunger-type grease gun or 
other device shall be used to force mortar through the wall, 
starting at the back face. A piece of burlap or canvas shall be 
held over the hole on the exposed surface and when the hole is 
completely filled the excess mortar shall be struck off with the 
cloth flush with the surface. Holes not passing entirely through 
the wall shall be filled with a small tool that will permit packing 
the hole solid with mortar, any excess mortar being struck off 
flush with a cloth. 


19. Wall Finish 


The exposed wall surfaces shall be finished by wetting, thor- 
oughly rubbing with a carborundum brick and rinsing. The top 
of the wall shall be finished as for walks. 


20. Floor and Walk Finish 


After the concrete has been brought to the established grade 
by means of a strikeboard, the screeds shall be removed and the 
space filled with concrete which is well worked into the adjacent 
slab. The concrete shall be floated with a wood float in a manner 
that will thoroughly compact it and provide a smooth, even sur- 
face. After the water sheen has disappeared the surface shall be 
lightly steel troweled, followed by a light brushing with a hair 
brush or other approved treatment to give a non-slip finish. 


Printed in U.S.A. 


Nolte: If a dusted-on color finish for the pool floor is desired, 
add paragraph 20(a): 
20(a). Dusted-on Finish 

The dusted-on mixture shall consist of 1 part portland cement, 
1 to 14 parts of dry aggregate and the required amount of color. 
All materials shall be proportioned by weight and the same 
amounts used in each batch. The materials shall be mixed dry 
in an approved mixing machine or mortar box until the color is 
uniform. After the base concrete has been screeded and the sur- 
face water removed, the dusted-on mixture shall be uniformly 
spread at the rate of not less than 125 lb. per 100 sq. ft. of area. 
The dry material shall be floated and worked into the slab, the 
first floating being stopped as soon as the surface becomes wet 
and the second floating withheld until surface moisture has dis- 
appeared. After the final floating, the surface shall be tested with 
a straightedge and high or low spots eliminated. Steel troweling 
shall be delayed until water sheen has disappeared. 


21. Forms 

Forms shail conform to the shape, lines, and dimensions of the 
concrete as shown on the plans. Lumber used in the forms for 
exposed surfaces shall be dressed to a uniform thickness, and shall 
be free from loose knots or other defects. Joints in forms shall be 
horizontal or vertical. For unexposed surfaces, rough lumber may 
be used. Lumber once used in forms shall have nails withdrawn 
and surfaces to be in contact with concrete thoroughly cleaned 
before being used again. 


22. Cleaning Reinforcement 

Metal reinforcement at the time concrete is placed shall be 
free from rust scale or other coatings that will destroy or reduce 
the bond. Where there is delay in depositing concrete, reinforce- 
ment shall be reinspected and, when necessary, cleaned. 


23. Bending 

Reinforcement shall be carefully formed to the dimensions 
indicated on the plans. Bends shall be made around a pin having 
a diameter of 6 or more times the least dimension of the rein- 
forcement. Reinforcement shall not be bent or straightened in a 
manner that will injure the material. Bars with kinks or bends 
not shown in the plans shall not be used. Heating of reinforcement 
will be permitted only when approved by the engineer. 


24. Placing Reinforcement 

Metal reinforcement shall be accurately positioned and secured 
against displacement by using annealed iron wire of not less than 
16 gage or suitable clips at intersections, and shall be supported 
in a manner that will keep all metal away from the exposed 
surfaces. The minimum clear distance between any bar and the 
nearest concrete face shall not be less than 2 in., unless specifically 
shown on the plans. 

Wire mesh used in the floor slab shall be lapped not less than 
6 in. on all sides and securely wired. 

Wherever it is necessary to splice reinforcement otherwise than 
as shown in the plans, the character of the splice shall be de- 
cided by the engineer on the basis of safe bond stress and the 
stress in the reinforcement at the splice. 


25. Construction Joints 

When necessary to provide construction joints not indicated 
on the plans, such joints shall be located and formed so as not 
to impair strength, watertightness or appearance of structure. 


26. Expansion Joints 

Expansion joints in the floor and walls shall be spaced not over 
60 ft. apart. The joints shall be filled with an approved material 
which will not run in hot weather nor become brittle when cold 
nor be affected adversely by water. The wall joints shall be pro- 
vided with a crimped copper strip to serve as a water stop. 
Special types of joints and joint fillers may be used when ap- 
proved by the engineer. 


27 


S4 


ee ns 


<2 
~* 
wemy ese 2 
wor 


ONION SCHOO 


ULB TH SHAUL 


€DUCATIONALE 
ARCHITECTURAL 
PLANNING 


The activities of the Portland Cement Association, a national 
organization, are limited to scientific research, the development 
of new or improved products and methods, technical service, pro- 
motion and educational effort (including safety work), and are 
primarily designed to improve and extend the uses of portland 
cement and concrete. 

The manifold program of the Association and its varied services 
to cement users are“made possible by the financial support of over 
65 member companies in the United States and Canada, engaged 
in the manufacture and sale of a very large proportion of all port- 
land cement used in these two countries. A current list of member 
companies will be furnished on request. 


Published by 


PORTLAND CEMENT ASSOCIATION 


All parts of exterior walls are cast in place in the Hollywood High School, Los Angeles. Grille work and rounded 2 
wall, equally well molded in architectural concrete, enclose a stairway. Marsh, Smith and Powell, Architects. 


FOREWORD 


ie urban and rural areas alike, construction of school 
~ buildings is far behind normal requirements. The 
situation today is probably not much better than some 
years ago when a special study showed that more than 
two million pupils were enrolled in buildings condemned 
as unsafe or unsanitary, or housed in portable or tem- 
porary quarters. More than half a million pupils were 
unable to attend school full time because of inadequate 
building facilities.* 

To overcome the serious shortage in school buildings, 
funds made available should be expended with the 
utmost economy, which must be clearly distinguished 
from cheapness. ECONOMY involves avoiding waste 
and selecting materials that endure. CHEAPNESS im- 
plies low cost of construction and high cost of 
maintenance. 

The avoidance of waste requires skilful planning of 
school plants so as to fulfill educational needs with the 
*Reported by William G. Carrin Architectural Record, September, 1935. 


greatest possible utilization of space and equipment. 
This subject, which is commanding increasing atten- 
tion, has been given a prominent place in this publica- 
tion. Framing plans, cross sections, various details and 
general layouts are presented to illustrate how portland 
cement concrete is used for safe, enduring—and yet 
economical—construction of schools. 

School authorities everywhere are striving to provide 
proper and sufficient school facilities for the American 
children who are now housed in unsafe, unsanitary or 
temporary quarters. It is in support of their efforts 
that this booklet is presented. 

It is desired to acknowledge the aid received in the 
preparation of this booklet from school publications, 
some of which are listed in the Bibliography. Grateful 
acknowledgment is especially due to Dr. HuBert C. 
Eicher, Director, Division of School Buildings, Depart- 
ment of Public Instruction, State of Pennsylvania, who 
has contributed valuable suggestions and criticism. 


The drawings in this publication are typical designs and should not be used as working drawings. They are intended 
to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform 
with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. 


CONCRETE IN SCHOOLS 


Educational and Architectural Planning 


A. EDUCATIONAL PLANNING 


1. INTRODUCTION 


Programs for new school buildings are planned through 
the combined efforts of school board, educator and 
architect. The responsibility for erection of school build- 
ings, their maintenance and operation, is generally en- 
trusted to the local boards of education. They may find 
it advisable to consult principals and teachers regarding 
arrangement of special rooms and to call in outside 
trained experts to make a thoroughgoing inventory or 
survey of the building situation. The architect’s pro- 
fessional services include conferences, preliminary 
studies, working drawings, large-scale detail drawings, 
specifications, and general supervision of the work. 

Because a building program cannot be conceived 
apart from the educational program, school buildings 
should be designed around the programs they are to 
house rather than—as has sometimes been done—forc- 
ing educational programs into buildings poorly adapted 
to their intended use. Educational problems which in- 
ject themselves at the beginning of the planning in- 
clude: (1) forecasting population and school enrollment; 
(2) establishing type of school administration and sub- 
jects to be offered; (3) determining space and equipment 
required; (4) adopting the most serviceable and econom- 
ical type of building plan. 


2. FORECASTING THE ENROLLMENT 


At the very beginning, the area to be served by the 
school must be established and the past and present 
population in this area be determined from available 
records. The probable extent and trend of future popu- 
lation growth must then be forecast, based upon careful 
studies. 

The distance pupils must travel should not be greater 
than one and a half miles for urban school; but the area 
served by the school should not be too small, because 
per capita expenses for operation of schools usually 
increase, the smaller the enrollment becomes. Studies 


show that the most economical elementary school plants 
are in the group having an enrollment of 500 or more. 

Within the school area, total population as far back 
as reliable records go may be determined from United 
States census or from sources such as records available 
in companies giving gas, water, electricity or telephone 
service. If total population in the past has been devel- 
oped graphically as illustrated by the solid lines in 
Fig. 1, future trends—indicated in dotted lines—may 
be estimated by extending the solid-line curve, giving 
due consideration to factors such as residential trends, 
transportation changes, industrial tendencies, and zon- 
ing programs. 


| 
1880 §=1900 1920 1940 


FIG. 1. After determining population in the past— 
plotted in solid lines—future population may be esti- 
mated as indicated in dotted lines, the height of the 
columns representing number of persons within the area 
to be served by the school. 


The school population—in the range from 5 to 19 
years of age—is between 25 and 35 per cent of the total 
population. The percentage for the United States be- 
tween 1880 and 1920, given in Fig. 2, is seen to be 
steadily declining. School population in the past may 
be plotted and the future trend estimated in a manner 
similar to that illustrated in Fig. 1 for total population. 
Regarding the proportion of school population attend- 
ing public schools, good information may be obtained 
by comparing total school population in the past with 
available census on record for public schools. 


36.4 35.6 34.4398 31.6 


FIG. 2. Height of columns indicates per- 
centage of persons between 5 and 19 
years of age in the United States. The 
percentage of “school population’ in- 
fluences the size of school plant and 
must be established before school facili- 
ties can be planned. 


1880 1900 1920 


Public school population being determined, division 
into age groups may be made by special surveys such 
as that carried out by Arthur B. Moehlman* who re- 
ports the following data for 10 city schools in 1923: 


Kindergarten 
Grades 1 to6 
Grades 7 to 9 
Grades 10 to 12 


From studies made as briefly outlined, initial enroll- 
ment to be anticipated may be fairly accurately deter- 
mined, future enrollment forecast and provisions made 
for possible future expansion due to increase in popu- 
lation. 

The correctness of surveys of anticipated enrollment 
is of great economic significance, since both over- and 
under-building may result in considerable waste of 
funds. 


6.5 per cent 
65.5 per cent 
19.5 per cent 

8.5 per cent 


3. SCHOOL ORGANIZATION 


Before the architect is called upon to make plans, 
certain educational policies must be defined by school 
board and educator, because the type of building is 
fixed by the type of school organization. 

Age groups were formerly divided into: (1) a grammar 
school with grades from 1 to 8, and (2) a high school 
with grades from 9 to 12; but since about 1915, the 
organization known as junior high school has gained 
ground rapidly. The modern organization has three 
groups instead of two: (1) an elementary school with 
grades from 1 to 6; (2) a junior high school with grades 
from 7 to 9; and (3) a senior high school with grades 
from 10 to 12. A choice must be made from among 
these and other organizational schemes available, be- 
cause each scheme requires a new distinctive building 
type. 

Schools were once organized so that a teacher met 
all her classes in the same room, or each classroom 
was reserved for the use of one grade only; but both 
of these arrangements were often wasteful because the 
rooms could be utilized part time only. Modern school 
organization strives for more efficient and, therefore, 
more economical utilization of classrooms by having 
as nearly as possible all rooms occupied during every 


*Page 334 in Public School Plant Program, see Reference No. 9. 
**Housing of High School Programs, see Reference No. 1. 


period of the day. The so-called platoon plan, to men- 
tion an example of modern organization, has won favor 
on account of its high degree of room utilization. Briefly 
described, it is a plan by which half of the pupils are 
accommodated in regular classrooms, while at the same 
time the other half are engaged in special activities in 
shops, laboratories, libraries, art, music or play. Proper 
schedule-making for school organizations of such types 
calls for a high degree of administrative skill but will 
give good educational return from a relatively small 
school plant investment. The building, naturally, should 
be laid out to house the particular curricular program 
adopted. 

Schedule-making and planning of organization are 
matters that in the highest degree affect the judicious 
expenditure of school funds. It is unwise to ignore the 
economy involved in good educational designing and 
equally unwise to offset the waste that may thus be 
incurred by lowering the quality of the building con- 
struction and equipment, or by neglecting playground 
facilities and landscaping. 


4. SPACE REQUIREMENTS 


In translating a given educational program into 
number of rooms required, the four significant elements 
are: 


(A) number of pupils registered in a subject; 

(B) average number of daily periods in a subject; 
(C) average size of class; 

(D) number of periods in the day. 


When these four elements are established, the number 
of rooms, N, required for any one subject, can be deter- 
mined from the formula: 


eA 
C xD 


Paul C. Packer has presented a thorough study of 
this problem in a book** in which he proposes to use 
the room formula with a correction added due to the 
fact that rooms cannot be occupied to capacity all the 
time. With minor modifications, Packer’s corrections 
are as given in Fig. 3 for school enrollments between 
200 and 1,000. 


FIG. 3. The percentage 
represented by column 
heights is to be added to 
the number of rooms de- 
termined by the formula 
proposed by Paul C. 
Packer. 2700 400 600 800 1000 
SCHOOL ENROLLMENT 


As an illustration of how to apply the room formula, 
let it be assumed that (A) school enrollment and num- 
ber of pupils taking English is 800; (B) each pupil has 


one daily period of English: (C) average size class in 
English is 30; and (D) school day has six periods. The 
number of rooms required for English is then: 
_ 800 X1_ 
30 X 6 
To allow for leeway in program-making since rooms 


are not being used to full capacity, add a correction 
which, taken from Fig. 3 for 800 pupils, is 8 per cent, or 


B xX 4.5 = 0.4. Total number of rooms for English 


is 4.5 + 0.4 = 4.9. 


100 

Compute similarly, number of rooms for each of other 
subjects taught in regular classrooms and determine the 
total number of classrooms that must be provided in 
the school. 


4.5 


The room formula applies also to subjects requiring 
special rooms such as laboratories and shops. Correc- 
tions for such rooms are presented in Packer’s book.* 


If specially equipped rooms are used considerably 
below their full capacity, every effort should be made 
to plan for duplicate use or maximum flexibility. As an 
example, it may be economical—particularly in small 
schools—to teach physics and chemistry in the same 
laboratory-classroom. Special plans, equipment and 
arrangement of same have justified this demonstrated 
economy. Floor plan and furniture layout in a combina- 
tion science laboratory-classroom designed for teaching 
of all sciences in a small school may be found in the 
publications listed in the Bibliography as References 
No. 18 and 19. A typical layout is shown in Fig. 4, 
which is taken with slight modification from a plan 


*See page 25 in Housing of High School Programs, Reference No. 1 


**Pages 3-7 in Standards for Junior High School Buildings, see 
Reference No. 17. Original list is very complete and comprehensive. 


pacer Fant 
= — 4 
—— ERPS SNP BE pe 


bibs | heal sabesbss feeder Ue) BESS CR aBEo 
5 FEET 


prepared by HuBert C. Eicher, Director, Division of 
School Buildings, Department of Public Instruction, 
State of Pennsylvania. 

Some types of special rooms used in modern schools 
are listed in the accompanying table, together with the 
usual size of rooms in terms of units, one unit being 
one-half the size of a regular classroom. The sizes are 
to be considered as a guide only, since the floor area 
per pupil accommodated may vary as to needs, age and 
equipment. “‘Frequency of occurrence” is taken from 
studies made by Garth H. Akridge** and gives number 
of times the rooms were included in 100 junior high 
schools erected between 1920 and 1931. 


Size Floor Area Frequency of 
Special Rooms In Units Per Pupil Occurrence 
Administrative Offices... 1 or 2 = 100 
Teachers’ Rooms........ Tor? 4 86 
Health Service Rooms.... 1 or 2 = 63 
Science Laboratories... .. 2 25 86 
Drawing and Art........ 3 25 71 
Miusic Roomiaues dss se 3 15 43 
Library or Study Hall... 4 15 83 
Foods and Cookery Lab... 2 or 3 25 94 
Commercial Rooms... ... 2 or 3 15 55 
Clothing or Sewing Lab. . 3 35 Te 
Industrial Arts Shop..... 4 35 89 


Educational layouts may be checked in regard to 
plant economy by counting all the “‘stations” or places 
that can be occupied by a pupil, such as desks in class- 
rooms, seats in reading rooms and assembly rooms, 
space available per pupil in gymnasium and shops. The 
ratio of total number of pupils divided by total number 
of stations is particularly significant and may be re- 
garded as an indicator of plant economy. For illustra- 
tion, a ratio equal to one—one pupil for one station— 
is unattainable, and schools with ratios greater than 
0.8—four pupils for five stations—are usually described 


a 
o i 


hs 


FIG. 4. Room in which sciences and other aca- 
demic subjects may be taught, designed for a 
small school to obtain a higher degree of class- 
room utilization. Combination furniture is to be 
designed especially for this room. The room 
may be lengthened and one or two student 
tables added if desired. The equipment layout 
is adapted from a design by Dr. HuBert C. 
Eicher. 


pats 


LEGEND 


B.B.: Blackboard. 

C.: Cabinet. 

D.F.: Drinking Fountain. 
S.: Sink. 

SH.: Shelves. 

ST.: Storage. 


T.D.: Teacher's Desk. 
V.: Vent Space. 


by their administrators as being crowded. If the ratio 
drops below 0.6—three pupils for five stations—authori- 
ties agree that the building is poorly planned and repre- 
sents a waste in expenditure. 


5. ORIENTATION AND PLAN TYPE 


When space requirements have been determined to 
care for the curricular activities, the various rooms must 
be put together in a group with proper view to orienta- 
tion and type of plan. 

Classrooms are oriented so as to have natural light 
from one side only, and the light is directed toward 
the left side of the pupils. North exposure in a room is 
suitable for art rooms but should otherwise be avoided, 
and direct south exposure is not desirable. Orientation 
of classrooms in the order of preference is usually rec- 
ommended as follows: south-east, east, south-west, 
west and south. 

At this stage of planning, small-scale sketches of the 
various rooms to be incorporated in the building may 
be cut out, the pieces put together and arranged accord- 
ing to certain plans. Whenever a possible arrangement 
is completed and the general outline of the plan drawn 
up, the pieces are removed to make another layout. A 
careful study of a number of such preliminary rough 
room layouts is often an important step toward obtain- 
ing the best possible educational plant with the least 
amount of capital outlay. 

The plans according to which rooms may be grouped 


are classified as closed or open plans. Closed plans are 
usually rectangular with center courts. Rooms facing 
the court or facing north have poor light, and it may be 
difficult or expensive to expand or extend a school 
built as a closed rectangle. 

Open plans are those in which all rooms have out- 
side light; they are named according to the letter the 
plan most nearly resembles and are classified as U, E, 
H, I, L, and T plans. The U- and E-plans have draw- 
backs similar to those of the rectangular plan; the 
H-plan is better but tends to be uneconomical except 
for very large buildings. 

The finest evolution of the basic plan is found in the 
I-, L- and T-plans. They are simple, easy to expand 
and give good orientation of all classrooms. The main 
distinction between these three plans lies in the arrange- 
ment of the gymnasium and auditorium, which may be 
placed: (1) one at each end (I-plan); (2) both at the 
same end (L-plan); or (3) both at the center of the 
main building (7-plan). Of these three types, the L-plan 
is now most in favor. 

In general, as the ideal in instructional space, orien- 
tation and expansibility is approached, the basic plan 
becomes more expensive to construct. It becomes a 
matter of importance to decide how much money to 
expend to approach the ideal in educational layout, and 
it is desirable to make some rough cost studies before a 
basic plan is adopted. " 


Main building, Lenox School for Boys, Lenox, Mass. A Colonial design for concrete by McKim, Mead & White, New York City, architects. Narrow 
rustications mark off wall into alternating wide and narrow courses. The building houses offices and classrooms and provides some dormitory space. 


B. ARCHITECTURAL DESIGNING 


6. REGULAR CLASSROOMS 


The classroom layout is an important element in 
school building designing, since most of the space is 
occupied by classrooms and, besides, special rooms are 
often planned in sizes equal to 14, 1, 11% or 2 times the 
regular classroom size. To make the classroom larger 
than it needs to be may result in considerable waste of 
space throughout the building. 

School authorities generally agree that the dimensions 
preferred for classrooms are: ceiling height 12 ft., width 
from 22 to 23 ft., and length approximately 30 ft. 
Shorter rooms are used in many high schools and longer 
rooms are advocated for classes in which special activity 
programs are followed. The desk layout and room size 
in Fig. 5 is considered standard for 40 sixth-grade pupils. 

Considerable difference exists in the choice and 
arrangement of the facilities that must be provided 
adjoining the classroom for wrap storage, vent space 
and storage of equipment. From the viewpoint of 
economy, the space or cubage occupied by the entire 
classroom unit stands out, and the reduction of cubage 
is a prime consideration as will be illustrated in the 
floor plans presented in this section and also in connec- 
tion with the framing plans to be studied in Section 15. 

When pupils have most of their classes in the same 


Te See ea ee 
| 


tg" 


$ = 
| 


‘o'd AISLES@ LS 17:0" 


“5 SEATS @7 


FIG. 5. Rectangular arrangement of 40 desks is used in 
most schools. Diagonal seating arrangement, see Fig. 7, 
gives better direction of light for both left- and right- 
handed pupils. 


room, their wraps may be stored within this room. 
Many elementary schools adopt the coatroom arrange- 
ment shown in Fig. 6, provide for vent space in the 
coatroom and make the corridor wall just wide enough 


FIG. 6. For lower grades, wraps are usually 


stored within classrooms. The floor plan 
shown may be modified by providing a read- 


ing alcove that occupies the central portion 
of the coatroom. The two door openings are 
then superfluous. 


= a a — ——— LEGEND 
[I+ }+-BEAMS EXPOSED B.B.: Blackboard 
|| IN CEILING C.: Cabinet 


D.F.: Drinking Fountain 
V.: Went Space 


DESCRIPTION 


Size of Classroom: 23x30 ft. 

Ceiling: exposed concrete, painted. 

Floor Finish: linoleum or composition tile 
in classroom, terrazzo in corridor. 

Wall: brick facing with concrete masonry 
back-up, or architectural concrete. 

Partitions: concrete masonry, painted. 

Floor Construction: reinforced concrete 
(see framing plan). 

Story Height: 12 ft. 41/2 in. (see Section 
15: Floor Framing). 


to accommodate cases, cupboards and columns as indi- 
cated. The total floor space required for the complete 
classroom unit is then approximately 1 ft. 6 in. wider 
and 5 ft. 6 in. longer than the classroom itself, or 
24.5 X 35.5 = 870 sq. ft. Since the door while being 
opened extends 2 ft. into the corridor, it is desirable to 
provide for increased corridor width, but this disad- 
vantage will be disregarded in the comparison of cubage. 
It is also a drawback that the coatroom occupies a great 
deal of the most desirable space near the exterior wall 
and that part of the floor space within the corridor wall 
is apt to be unassigned and therefore wasted. 


If wraps are to be stored within the classroom, a 
better arrangement is that shown in Fig. 7 with ward- 
robes in the corridor walls accessible from the room. 
The floor area for each classroom then becomes about 
26.6 X 30.5 = 810 sq. ft. This is a reduction of 7 per 
cent compared with Fig. 6 and is true economy, for the 
reduction in floor area is obtained without impairing 
service or quality. The wardrobe layout in Fig. 7 makes 
the entire space near the exterior wall available for 
instructional use, it provides better vent space, and the 
doors, being completely recessed, do not extend into 
the corridor. In most schools where wardrobes are used, 
they are in the back of the classroom, but it is more 
convenient to have them near the door. It is also better 
to place the wardrobes in the part of the room which is 
least desirable for instruction and where they can be 
connected directly to the vertical vent shafts. Black- 


FIG. 7. Wrap storage may conveniently be provided 
along the corridor wall by wardrobes that open into 
the classrooms or by lockers accessible from the 
corridor. Either layout adds little floor area to that 
of the classroom. The type of diagonal arrangement 
of desks shown is gaining favor. 


LEGEND 


B.B.: Blackboard 

C.: Closet 

D.F.: Drinking Fountain 
T.D.: Teacher's Desk 
V.: Vent Space 

W.: Wardrobe 


DESCRIPTION 


Size of Classroom: 23x30 Ft. 

Ceiling: plaster on metal lath. 

Floor finish: linoleum or composition tile in class- 
room, terrazzo in corridor. 

Wall: brick facing with concrete masonry back-up. 

Partitions: concrete masonry, painted. 

Floor Construction: reinforced concrete (see framing 
plan). 

Story Height: 12 ft. 10 in. (see Section 15: Floor 
Framing). 

Lockers: accommodate two pupils each. 

Seats provided for some left-handed pupils. 


board should not be placed on the rear wall but on the 
wall opposite the windows, and wardrobes arranged as 
in Fig. 7 are therefore to be installed with blackboard 
attached to the front of doors. 


In schools where a grade may be moved frequently 
from one room to another in the course of a day, it is 
preferable to provide lockers that are accessible from 
the corridor, an arrangement which is illustrated in the 
lower portion of Fig. 7. It is customary to require that 
1 ft. be added to the corridor width for service space in 
front of each tier of lockers, and the floor area actually 
occupied by the classroom unit in the lower part of 
Fig. 7 then becomes about 30.5 X 27.2 = 830 sq. ft. 
Fig. 7 illustrates how to make arrangement in the corri- 
dor walls for cabinet, drinking fountain, and lockers 
which accommodate two pupils each. 


In the layouts illustrated, columns of reinforced con- 
crete are flush with the inside walls in the classrooms 
and concealed within the wall construction. Examples 
of floor framing designed for the floor plans in Figs. 
6 and 7 will be given in Section 15. 


A construction feature which may be introduced 
under certain conditions is illustrated in Fig. 7. Each 
half of the classroom may be laid out as a self-contained 
unit that functions independently of the other half of 
the room. By merely shifting the partitions, a new series 
of rooms may be built economically if it becomes neces- 
sary at some future time to alter the room arrangement. 


Random ashlar masonry is used with pleasing effect in gymnasiums. The concrete blocks shown are 
made with lightweight aggregate and are not painted. The lower 6 ft. of the walls are veneered, 


7. SEATING IN CLASSROOMS 


From the viewpoint of the architect, the question of 
whether the pupils’ desks should be fixed or movable is 
of importance. With fixed furniture, the tendency is to 
choose a floor finish of wood. On the other hand, a 
finish of linoleum or composition tile laid on the struc- 
tural concrete slab is preferable when the furniture is 
movable. Some trends in classroom seating will be 
briefly discussed. 


The traditional arrangement is shown in Fig. 5, in 
which 40 desks placed in five tiers and eight rows are 
fastened to the floor. One serious objection to this rec- 
tangular seating is that pupils look into bright glare of 
light from windows. This causes injurious eye strain, 
makes the pupils stoop over their work and reduces 
their power of attention and concentration. For left- 
handed pupils, the direction of light is, of course, wrong 
and the seating most undesirable. 


Educators have experimented to overcome the handi- 
cap of improper direction of light, and as a result, the 
desk arrangement shown in Fig. 7 has been adopted in 
many schools. The diagonal layout is found to be 
superior to the rectangular layout because the desks 
are in the ideal relation to the light which comes from 
behind over the left shoulder; and a number of seats 
may be placed in ideal position for left-handed pupils 
as indicated in the upper right corner in Fig. 7. It is 
also advantageous that the aisles are directed diagon- 


ally, giving more direct access from entrance to seats, 
and writing on the blackboard on the inside wall may 
be observed more conveniently by all pupils. 


The school administrator may wish to interchange 
between rectangular, diagonal and small-group seating 
arrangement; the number of left-handed pupils may 
change from year to year; and the height or type of 
desks may have to be changed periodically. For these 
purposes, it is doubtlessly better to have movable furni- 
ture and to specify linoleum or composition tile floor 
finish laid on concrete slab. Frictional resistance be- 
tween top of floor and bottom of desk may be increased 
by attaching shoes of rubber to the furniture; this pre- 
caution will keep desks in place, protect floor finishes, 
and reduce noise. 


8. GYMNASIUMS 


In warm climates, play space may be provided for 
pupils in the form of outdoor gymnasiums with a con- 
crete roof supported on columns, a concrete floor slab 
placed at ground level, and walls on one or two sides. 
This type of structure may be used for many school 
purposes, as will be discussed in Section 20. 


Indoor gymnasiums, which are required in colder 
climates, should offer advantages similar to those of 
the outdoor gymnasium. The floor is preferably at 
ground level with direct access to the playground, and 
ample window area—approximately 20 per cent of the 


40-0" 
LINES IN COURTS LESS 
THAN 75-0" LONG 
CENTER CIRCLE 


THESE LINES I" WIDE 
ALLOTHER LINES 2° WIDE 


FIG. 8. The size of basketball courts may vary, but the 
court layout usually governs the shape of gymnasium. 


floor area—is provided in the longitudinal walls. Sky- 
lights are objectionable because they give too much top 
glare for ball players. 

The gymnasium should be large enough to provide 
40 sq. ft. of floor area for each pupil accommodated and 
is usually made to fit the layout of a handball court. 
For this reason, a room 48x80 ft. is considered minimum 
for young players, but 56x90 ft. is a better size for pupils 
of high school age. A basketball court of minimum size 
is shown in Fig. 8. A margin at least 3 ft. wide is re- 
quired between outside court lines and wall surfaces. 

The height of gymnasium varies from one to two 
regular story heights. For a height of 6 ft. above the 
floor, all pipes and radiators must be recessed and 
screened and the wall finish be made smooth by using 
a wainscoting of concrete masonry, cast stone, glazed 
brick, pressed corkboard or linoleum. Above the wain- 
scoting, a concrete block wall such as illustrated in the 
photograph on the preceding page (ashlar pattern) is 
of pleasing effect. 


CONCRETE FINISH F270 
CONCRETE SLAB 


WATERPROOF 
INSULATION - 


CONCRETE BASE 
COURSE es 
CINDER FILL ———-~ 


INSULATED 


FIG. 9. Floor finishes in 
gymnasiums are of 
wood. Inall other rooms 
and in corridors, con- 
crete floors are used 
with a finish of con- 
crete, linoleum or com- 
position tile. 


CONCRETE SLAB ON FILL 


DIVIDING STRIPS 


TERRAZZO 
FINISH 


MORTAR BASE 


CONCRETE SLAB 


TERRAZZO 
FLOOR FINISH 


10 


Since a certain degree of resilience is desired, gymna- 
sium floors have a wood finish and subfloor laid on 
sleepers. To provide firmness, sleepers should be set on 
and securely fastened to a base slab of reinforced con- 
crete. A detail of this construction is shown in Fig. 9, 
which also gives details for concrete slabs and finishes 
suitable for floors in rooms other than gymnasiums. 
For an example of roof construction consisting of a 
reinforced concrete three-hinged frame with bleacher 
cantilevered from wall columns, see Reference No. 14. 


9. ASSEMBLY ROOMS 


Many schools have been constructed with gymna- 
sium and auditorium combined, ostensibly to make 
duplicate use of one room. The plans were to provide a 
large auditorium in which the entire school population 
gathered—on rare occasions—to listen to formal pro- 
grams. In many instances, however, the result was 
that the space reserved for gymnasium-auditorium was 
utilized inefficiently. 

The trend in modern school planning is to build one 
room just large enough for gymnasium and another 
small room where groups of pupils assemble regularly 
and participate in informal educational activities. An 
assembly room 40x60 ft., including a stage and seating 
for about 250 pupils, is considered large enough for 
most medium-sized schools. Properly administrated, 
the assembly room will give excellent educational re- 
turn and be economical in layout and operation, since 
it permits a reduction in the number of classrooms. 

In the small assembly room, floors need not be sloped. 
Concrete base slab overlaid with linoleum (see Fig. 9) 
and fixed seats in curved or straight rows are standard 
layout. Wall construction may be of concrete block laid 
in random ashlar, similar to that in gymnasiums. Such 


TE] LINOLEUM OR ak 
COMPOSITION TILE FSS 75 ZO GO 


wo 
“=| PADDING 
=| CONCRETE SLAB 


LINOLEUM OR 
COMPOSITION TILE FINISH 


FINISH FLOORING 
SUB-FLOORING 
BUILDING PAPER 
SLEEPERS 


CONCRETE SLAB 
DRAINED 
CINDER FILL 


WOOD FINISH FOR 
GYMNASIUM FLOORS 


4 
READING ROOM —o 
i f 5 FEET 
ee i se do Dr 
IEE Saeed 
1 I ] T T : 
CONFERENCE | | 
ROOM paar | ill aes 
- Rica erat et th 
= eae T T T T T | COAT 
9 | |ROOM 
Wn 2 Bea rans ie ah ae : 
a WORK ROOM 
O 
| : | 
B.B. ; +7 | 
os ase atic | 
aa is TTT be 


FIG. 10. Typical layout for elementary school of medium size includes main reading room, small conference room and working room 
for librarian. Since the reading room is the “‘living room" of the school, decoration is made attractive, yet simple and dignified. 


LEGEND 
B.B.: Bulletin Board Size of Reading Room: 30x40 ft. 
C.: Catalogs Ceiling: concrete with acoustical plaster. 


D.: Dictionary Stand 


T.: Table 
V.: Vent Space 


back-up. 


architectural treatments as illustrated are pleasing, yet 
simple and inexpensive. 

The hazards due to fire, windstorms or earthquake 
are nowhere greater than in the assembly room. There 
is generally no choice left but to make walls and ceiling 
absolutely fireproof as well as rigid and stable against 
lateral forces. Reinforced concrete beams and columns 
rigidly joined to form portals or frames* provide the 
suitable type of construction where safety, strength 
and beauty must be combined with economy. 


10. READING ROOMS 


The school library is a large unit which should be 
given special attention in educational and architectural 
planning. Good planning and administration of the 
library raises the utilization factor of the school as a 
whole, and—as has been demonstrated in Section 4— 
a high factor of utilization signifies economy. 


*Detailed design procedures illustrated with numerical examples 
for a single span frame are given in One-Story Concrete Frames Ana- 
lyzed by Moment Distribution, free copies of which are available in 
U.S. and Canada by request to Portland Cement Association. Useful 
information is also available in Analysis of Small Reinforced Concrete 
Buildings for Earthquake Forces. 


Floor Finish: linoleum or composition tile. 
L.D.: Librarian’s Desk Wall: brick facing with concrete masonry 


DESCRIPTION 


Partitions: concrete masonry. 

Floor Construction: reinforced concrete. 
Story Height: 12 ft. 414 in. 

Book Shelves where indicated. 


To gain maximum utilization, the reading room may 
be assigned as study hall for pupils during regular class 
periods and—outside such periods—be used for recre- 
ational and voluntary reading. The seating capacity 
should be not less than one-tenth of the average daily 
school attendance for reading room purpose, but some- 
what greater when the room serves also as a study hall. 

The layout in Fig. 10 illustrates a typical reading 
room for a school with about 800 pupils. In the main 
room, which is 30x40 ft., seats are arranged at separate 
tables for 60 pupils. By adding the tables indicated by 
dotted lines, the number of seats may be increased to 
80. No part of the tables is more than 19 ft. from the 
windows, the inside aisle being used for vents, doors, 
shelves, stands and librarian’s desk. A small room for 
conferences and a work room for the librarian are often 
arranged as shown in Fig. 10. The location preferred 
for the library is on the second floor near the center of 
the building, and the regular ceiling height of 12 ft. is 
sufficient. 

Reinforced concrete columns, laid out in Fig. 10 to 
give an economical floor framing, are concealed and 
occupy little useful floor area. The ceiling construction 


11 


indicated by dotted lines consists of a 4-in. solid con- 
crete slab reinforced as illustrated for a classroom in 
Fig. 14 (see Section 15). The slab is supported by beams, 
30 ft. long between columns. The beams may be left 
exposed in the ceiling. 

Noise must be eliminated as much as possible in 
reading rooms, and acoustical cement plaster is there- 
fore to be applied to surfaces in ceiling but not to walls 
of lightweight concrete masonry which, in itself, is a 
good sound-absorbing material. Sound-absorbing floor 
covering—such as linoleum, cork, or rubber plates— 
may be laid on reinforced concrete floor as shown in 
Fig. 9. 


11. CORRIDORS 


Schools have been built with non-fireproof construc- 
tion in and around classrooms, a practice which is not 
recommended. No such compromise should be toler- 
ated in the planning of corridors. School authorities 
agree that corridors and, of course, stairways must have 
walls and floors constructed of fireproof materials. 

The clear width is usually taken as 12 ft. for main 
corridors, 10 ft. for secondary corridors, and 8 ft. for 
corridors with rooms on one side only; but special study 
must be given to spaces adjoining large rooms. Every 
effort should be made to provide natural light, and 


*Free copies available in U. S. and Canada by request to Portland 
Cement Association. 


corridors should therefore be extended to or through 
outside walls. To reduce hazards in case of panic, sad- 
dles, thresholds, changes of level, blind pockets and 
dead ends must be avoided as much as possible. 

Arrangement of lockers, doors and recesses in corri- 
dor walls is shown in Figs. 6 and 7 for classrooms, in 
Fig. 10 for a reading room, and in Fig. 11 for area near 
a stairway. Typical corridor layouts are illustrated in 
the photographs on this and the opposite page. 

The construction of the walls in the photograph 
below is concrete masonry painted so as to give the 
pleasing effect illustrated. The lower 6 ft. of the con- 
crete masonry usually has a wainscoting which may be 
of cast stone, glazed brick or linoleum. In the photo- 
graph opposite, walls are of architectural concrete with 
a coat of portland cement paint. 

The concrete floor finish marked off in squares shown 
in the photograph opposite is wear-resistant. Either this 
type or a terrazzo finish (see Fig. 9) is recommended on 
account of the particularly heavy wear to which corri- 
dor floors are subject. Detailed information on how to 
place and treat floors is presented in the booklet entitled 
Concrete Floor Finishes.* 

The ceiling is of exposed painted reinforced concrete 
in the photograph opposite, but a suspended ceiling of 
plaster on lath as illustrated in the photograph below 
is sometimes required to conceal flues and pipes. 


Concrete masonry painted a light gray or buff is well suited for construction of corridor walls. The 
lockers are recessed, taised 4 in. off the floor, and the masonry around the lockers is veneered. 


a2 


An appearance of cleanliness and beauty is produced in the all-concrete corridor 


in Upland Junior High School, Upland, Calif. G. Stanley Wilson, Architect. 


12. STAIRWAYS 


Certain safety features are indispensable in the con- 
struction of stairways. The stairs shall be of fireproof 
material, shall have fire-resistive enclosures, and be re- 
moved from all fire hazards. There shall be no well-hole 
between runs of stairs, and all stairways from upper 
floors shall extend to ground level. The balustrade shall 
be about 5 ft. high, the lower part of which is to be 
solid. The width of tread (exclusive of nosing) multi- 
plied by the height of riser shall equal between 70 and 
75, all measurements being in inches. 

Width of stairs for schools is usually given in multi- 
ples of 22 in., which may be termed a stair unit. The 
following formula* is recommended for determination 
of stair width: 


: : Gross Area per Floor 
Number of stair units = vei Nae eed ek Ue 


2400 


the floor area being in square feet. 


*From Building Exits Code, 7th Edition, 1943, Section 2135, 
National Fire Protection Association. 


Close-up of partition in school shows the attractive 
appearance of concrete masonry. The cinder 
blocks, laid in American bond, are 8x4 in. in size. 


13 


. CONCRETE STAIR LAYOUT 


of SCALE -$"= 1-0" 


o- 8" 1 _ IO-TREADS @ 11" 9°2" 6:6" 


¢ 
) 
© 
CY 
5°SOLID SLAB er 
7$-G'0.C.ALT.BARS BENT = 
TRANS. BARS z'®PERTREAD)| 
a) ae 
@ 
zi 5 
che 
i) 
1) 
i : cf 
Se a 
Zo ‘f 
: Go : 
Z = 
ue ip ae 
ares Ze. tee 
SECTION ATA 
SCALES. 21:0" 


FIG. 11. Stairs with 22 risers, each 63/4 in. high, are laid out for the minimum story height of 12 ft. 41/2 in. obtainable with framing shown 
in Fig. 14. The construction incorporates safety features considered necessary for stairs. Stair widths are usually made in multiples of 22 in. 


14 


For illustration consider a three-story school build- 
ing with 12,500 sq. ft. of gross area on each floor. Stairs 
12,500 
= 5.2 

2,400 
units wide. Assuming there are two stairways, the width 
3X22 _ 

12 


leading from upper floors shall be at least 


of each stair is “S = 2.6, say, 3 units, or 


5 ft. 6 in. 

The typical stairway layout in Fig. 11 includes a 
floor plan showing the stair hall completely cut off from 
fire hazards by an enclosure of reinforced concrete. 
Note that ample natural light has been provided and 
dead pockets have been eliminated. The width is suffi- 
cient to let three pupils walk abreast. 


Section A-A in Fig. 11 shows the usual construction 
of stair slab of concrete—5 in. thick—cast integrally 
with the concrete steps, the slab being supported by 
transverse beams as shown. A non-slip concrete fin- 
ish may be applied, or precast* treads placed as illus- 
trated in Fig. 12. 


i3mLOLOETS 


It is highly objectionable to place toilet rooms for 
pupils in the basement. Such rooms must be provided 


ce *Free copies of Cast Stone Service Bulletins, dealing with the use of 
rast stone for various purposes, are available in U. 8. and Canada by 
equest to Portland Cement Association. 

**Public School Plumbing Equipment, see page 120 in Reference 
No. 6. 


on each classroom floor. Long and narrow rooms with 
windows on the long side are most suitable. Maximum 
exposure to sunlight is essential. To avoid spreading of 
odor, ventilation shall be direct to the outside of the 
building and not connected to the regular ventilation or 
heating plant. 

M. W. Thomas** has recommended that the number 
of fixtures be as follows: 


Lavatories 
in Toilet 


Rooms 


Boys’ Boys 
Water 
Closets 


Stall partitions and walls to a height of at least 6 ft. 
shall be of a material that contributes to cleanliness, 
is permanent, is difficult to mark or scratch and is easy 
to clean and maintain. Cast stone with highly polished 
and dense surface answers these requirements. 


Floors shall be as impervious to water as possible 
and be built with surface sloping to a floor drain. 
Terrazzo laid as in Fig. 9 in sections divided by brass 
strips and highly polished gives an excellent, permanent 
floor finish. 


Ze Hi I" TREAD 


iz 
HW" TREAD 


Pos 


ait 
S 


CONCRETE 
FINISH 


+"RAD. 


[-4 
FIG. 12. Stair finishes may be 
either precast or cast-in-place con- 
crete, and the treads have non-slip 
surface. 


Ep eae 
0/- ZREIN FORCED 4: 


SLC: CONCRETES I 


CONCRETE NON-SLIP TREADS 
SCALE -[57 = 170° 


15 


Main facade of Lincoln School, one of two concrete buildings constructed in lola, Kan., to replace 
five obsolete schools. Both buildings were designed by Lorentz Schmidt, architect of Wichita, Kan. 


C. STRUCTURAL DESIGNING 


14. INTRODUCTION 


Since school attendance is not voluntary but com- 
pulsory, it becomes an inescapable moral and legal 
obligation to safeguard school children’s lives with a 
maximum of precautions. This obligation, it is asserted, 
charges school authorities with the duty to build noth- 
ing less than the safest type of structure. 

The safety demands are incontestable and need not 
be supported by any allusion to disastrous school fires. 
The only subjects open to arguments are those dealing 
with cost and type of firesafe construction. 

John W. Sahlstrom, who has made significant and 
thoroughgoing studies of safety features in school 
buildings, quotes in his book* a school superintendent 
who gives a brief and true resumé regarding cost and 
type. He distinguishes between degree of firesafety in 
construction by describing as Type B: “A building of 


*Some Code Controls of School Building Construction in American 
Cities. See Reference No, 21, page 74. 


16 


fire-resistive construction in its walls, floors, stairways 
and ceilings, but with wood finish, wood or composition 
floor surface, and wood roof construction over fire-resistive 
ceiling’ ... and as Type C: “A building with masonry 
walls, fire-resistive corridors and stairways, but with 
ordinary construction otherwise, 1. e., combustible floors, 
partitions, roofs and finish.” 

In conclusion, he asserts that “ ... as it has been 
repeatedly proved that the difference between the cost of 
Type B and Type C buildings is often as low as 5 per 
cent and seldom above 10 per cent, it is extremely unwise 
to attempt a saving in this direction, if for no other 
reason than to safeguard child life. The factors of insurance 
rates and maintenance charges are financial considera- 
tions which militate against any type of construction 
below that of Type B.” 

With respect to the importance of protecting prop- 
erty, comprehensive surveys disclose that the ratio of 
fire loss in buildings of ordinary as against fire-resistive 


construction recently has been more than 9 to 1,* an 
unusually high ratio of fire loss which weighs heavily 
in favor of fire-resistive construction. 


The continuity, rigidity and permanence of fire- 
resistive construction such as reinforced concrete makes 
for minimum cost of maintenance, upkeep and replace- 
ment. School buildings—especially the large, crowded 
rooms in them—can not be pronounced safe unless they 
are designed to resist earthquake shocks or destructive 
windstorms. 


In first cost—contractor’s bid price—the safest and 
best construction is, usually, the most expensive. How- 
ever, when all expenditures (including insurance, main- 
tenance and replacements) are properly accounted for 
in the bookkeeping, the best construction becomes the 
most economical as well. Maintenance and insurance 
costs are particularly significant guides in selecting 
materials; but even if proper bookkeeping is neglected, 
other factors—such as safety—which are not subject 
to definite cost analysis combine to leave no choice 
but to provide the best type of structure. 


Examples of structural details will be presented in 
the sections that follow. Besides strength and rigidity, 
reduction of cubage or building volume will be given 
particular attention. To provide the same facilities in a 


*See p. 37 in Fire and Other Insurance for Public School Property, 
by H. C. Roberts, Proceedings National Association of Public School 
Business Officials, 1930. 


**p.s.f.—pounds per square foot. 


safer durable building occupying less total volume is the 
essence of true economy in school construction. 


15. FLOOR FRAMING 

Let it be assumed that a floor framing is to be laid 
out for the classroom plan shown in Fig. 7. Four rows 
of columns, one row in each of the walls, are arranged 
for the sake of economy in design so as to give minimum 
length of classroom span. 

Concrete joist floors—as in Fig. 13—are economical 
for the long spans and light loads prevailing in class- 
rooms. The typical loads on this slab are: 


Live load = 50D sal. 
Linoleum finish = 5p.s.f. 
Suspended ceiling = 10 p.s.f. 
Slab: 6-in. joist + 3-in. topping = 55 p.s.f. 
120 p.s.f. 


With 20 in. wide metal forms and 6 in. wide concrete 
joists between them, the load per joist 1s: 


w = 120 X ~ = 260 lb. per lin. ft. 


If the over-all length of the metal forms is 1’ = 22 ft., 
the total depth of the joists is 9 in., and the effective 
depth d = 9.0—1.5 = 7.5 in., the maximum unit 
shear, v is: 

_ Yul! _ 0.5 X 260 XK 22 
el en ah ri aa 

Reinforcement, A,, required in each joist is: 


= 73 p.s.l. 


Yeul? 14X 260 X23.52X12 
pe CEE = EES EE rye tia 
+ “df.” 0.875X7.5X20,000 "84-0 


Reinforced concrete 
beams with solid con- 
crete slab spanning 
about 10 ft. between 
beams above class- 
rooms are used in 
schools erected under 
the jurisdiction of the 
Public Improvement 
Commission, City of 
Baltimore, H. J. Liem- 
bach, Supervising En- 
gineer for the city of 
Baltimore. Suspended 
ceiling is omitted and 
plaster, stain or paint 
may be applied direct 
to the concrete. 


a7 


= 


Use two 1-in rd. bars (area = 1.58), one of which is 
straight, the other bent.* 

A 4-in. wide bridging joist, reinforced with one 54-in. 
rd. bar in both top and bottom is added along the 
center-line of the span. 

The partitions between classrooms were formerly 
supported by beams with webs extending below fin- 
ished ceiling, but the ceiling may be made flush through- 
out as in Fig. 13. In the construction featured in Phila- 
delphia Public Schools,** one row of metal forms is 
omitted under each partition as indicated, thus provid- 


*A theoretical deficiency of 1.64-1.58=0.06 sq. in. exists in tensile 
steel area. This is allowed because the moment of gw? is considered 
conservative in this type of framing in which torsional resistance of 
supporting beams tends to reduce the positive moment near midspan of 
the ribs. 

**See Shallow Concrete Floor Developed by Philadelphia Schools, 
Reference No. 20. 


ing a beam 9 in. deep and 32 in. wide reinforced with 
ten l-in. sq. bars, five in top and five in bottom of the 
shallow beam. 

The type of beam framing used in walls and corridor 
is indicated in Fig. 13. The spandrel beams are up- 
turned so that their soffit is 11 ft. 9 in. above the floor 
surface below, a dimension which is usually maintained 
to provide sufficient light for pupils in the interior of 
the classroom. 

The total depth required for the slab construction in 
Fig. 13 is remarkably low—only 10 in., including 1 in. 
for floor finish and ceiling plaster. With the standard 
clear ceiling height of 12 ft., the story height is as little 
as 12 ft. 10 in. No other construction with flush ceiling 
has a shallower floor design; but a still smaller story 
height may be obtained with a construction having two 
beams exposed in the ceiling of each classroom. 


FIG. 13. Concrete joist 
floors with flush ceiling, 
featured in Philadelphia 
public schools, require a 
story height of only 10 
in. more than the clear 
height required in class- 
rooms. This framing plan 
corresponds to the floor 
plan in Fig. 7. 


3-3°OSTR.IN OP 


jo 
SECTION MA & 


SCALE-}"=1°0 


18 


REINFORCED WITH MESH 


_pFABRIC QR BAR MAT /—10-1"S@.BARS 
se Ta ERE AIS rae ie SNe ast eh aise: 
O'e| 20° | 32" 20” |¢_ 20° 
ETeDk S ae 
| BLE STR. 
SECTION B-B 
SCALE-}"= 120" 


The floor framing with exposed beams shown in Fig. 
14 is laid out for the floor plan in Fig. 6; but this type 
of framing is, of course, equally suitable to a floor plan 
such as in Fig. 7. The typical loads on slab A in Fig. 
14 are: 


Live load = 50 p.s.f. 
Linoleum finish = 5 p.s.f. 
Slab 4in. thick = 50 p.s.f. 

105 p.s.f. 


With a clear span of approximately 9 ft. between 
beam webs, the slab reinforcement required is: 


1 1 

= wl? — x 105 X92 12 
A a es ee ee =0.16 sq. in 
+ “jdf, ~ 0.875 X3X20,000. °°. 


Use 3%-in. rd. bars at 71% in. o.c., alternate bars bent. 
On each of the two beams above the classroom, the 


load per lin. ft. is: 


Slab: 105 X 10 = 1050 lb. 
Beam: 1.33 XK 150 = 200 lb. 
w = 1250 lb. 


With beams 12 in. wide (6), 20-in. total depth, and 
18-in. effective depth (d), maximum unit shear is: 


_ Yul _ 0.5 X 1250 x 23 
einen?) Soe as 
Reinforcement required in each beam is: 


= 76 p.s.i. 


Yewl? 14X1250X 24212 
A,=4 = AO 3.43 sq. in. 
jdf, 0.875 X18 X 20,000 


Use two 1-in. sq. straight bars and two 1-in. rd. bent 
bars. 

In this framing, the distance from floor to soffit of 
spandrel beam is again made 11 ft. 9 in.; but the story 


CORRIDOR FLOOR CONSTRUCTION TO 

BE EITHER SOLID SLAB REINFORCED IN 
ONE DIRECTION (AS INDICATED), SOLID 

| SLAB REINFORCED IN TWO DIRECTIONS, 


| OR JOIST SLAB SIMILAR TO THAT IN OTHER 
ERANINGOR EL Neer ea 


BENT BAR 


FRAMING PLAN 


LE -1!0" 


SN tik 


CORRIDOR 


Be ee N-sTRAIGHT BAR 
# TL pcemnune 


FIG. 14. Slab-and-beam 
construction gives sim- 
ple framing and the 
smallest story height. It 


| 

| 

| 

| 
SLAB AT | is an economical rigid 
| 


Waviiy 


construction suitable for 
both floors and roofs. 


| 
| 


Hosssss 


SECTION A-A 
SEGRE = gl "Os 


| EXPOSED CONC.CEILING = 
SECTION B-B 2 
SCALE s = 1-O; = 


19 


Faculty dining room in Evanston (Illinois) Township High School is a beautiful example of concrete 
joists and beams exposed in the ceiling. Simple, inexpensive decoration available in many variations 
may be applied to give each room its distinguishing character. Hamilton, Fellows and Nedzed, Architects. 


height from floor to floor is reduced to 12 ft. 414 in.— 
the floor construction being, in effect, only 414 in. deep. 

Compare the story height of 12 ft. 41% in. with that 
required for ordinary construction, which is approxi- 
mately 13 ft. 5 in. The reduction in the height and also 
in the cubage of the building is 8 per cent, which repre- 
sents a considerable saving in construction of walls, 
stairs, columns, partitions, vertical pipes and flues. An 
additional saving accrues when the plastered ceiling is 
eliminated, as may be done in the framing in Fig. 14. 
The slab-and-beam construction illustrated is doubt- 
lessly an outstanding example of true economy, since 
service requirements have been maintained, a durable 
rigid floor constructed, and, withal, the building volume 
has been reduced 8 per cent. 

The use of dressed lumber or form lining will leave 
the concrete smooth and ready to receive simple, inex- 
pensive surface treatments such as portland cement 
paint, staining, stenciling, or perhaps a thin layer of 
portland cement plaster. With floor finishes such as 
linoleum laid on padding or various types of composi- 
tion tile, transmission of noise from story to story is 
deadened by the floor in a fully satisfactory degree. 

Decorated concrete ceilings are considered more at- 
tractive (see photograph above) than monotonous cal- 
cimined ceilings, and they offer excellent opportunities 
for the architect to give each room a different decoration. 


*An Achievement in School Construction, see Reference No. 8. 


20 


! 


Warning is often sounded against the use of floor con- 
structions with too light weight, a warning that is 
especially well justified in schools. Action in unison 
when pupils march or jump is apt to create vibration in 
floors but especially in those that are light and made 
of several independent parts, the result being that floors 
squeak and plaster cracks. 

Virgil L. Johnson sums up facts about vibration in 
schools in saying :* 


“Rigidity of construction is an essential fea- 
ture of all school buildings. Concrete construc- 
tion of the monolithic type is especially well 
adapted for use in schoolhouses because it can 
be so designed that there will be no vibration in 
any part of the building either from school 
activities or from the traffic of the adjoining 
Sirecim 


16. FRAMING SCHEDULES 


To convey complete information to the builder 
regarding the concrete structure, framing plans are 
augmented with sections and schedules such as those 
illustrated in Fig. 15. 

Solid concrete slabs are described by writing on the 
framing plan depth of slab and size and spacing of rein- 
forcement; but footings, columns, joists and beams are 
merely given a mark on the plan and each mark repeated 
in a schedule where the necessary data are written as 
illustrated. 


Footings under columns in schools are almost always 
square separate footings and are dimensioned as in Fig. 
15. Under walls, narrow and continuous footings are 
used and reinforced as illustrated in Fig. 16. 

A column is usually marked with a numeral which 
corresponds to that given the supporting footing, and 
the design is described by gross size of cross section 
number and size of longitudinal bars, size, pitch and 
diameter of spiral. Ties or hoops may be substituted for 
spirals. 

Three types of joists are illustrated in Fig. 15, the 
distinction being in the method of forming the joists. 
Reinforcement in the slabs—or topping—at right angles 
to the joists may be bars or steel fabric and is usually 


-DOWELS. SAME 
i 4 NUMBER & SIZE 
NO CONST, LEY AS BARS IN COL 


JOINT 


TYPICAL SQUARE COLUMN FOOTING 


STR.CONT —TBPM-CLOSED 


) 


baal UPTURNED BEAM 
SIRE DS JSBENT 8 | STRAIGHT BS BENT 


TYPICAL INTERIOR BEAMS © TYPICAL SPANDREL BEAMS 


Thou! 


PANEL OF 
WOOD FORM 


TE 
ORMS TYPICAL JOIST CONSTRUCTIONS 


FLR 
oe 
COLUMN 22 
DETAILS ie 
38 
TIES 28 


called for on the framing plan or in general notes. 

Typical interior beams and spandrel beams—includ- 
ing upturned beams—are sketched in Fig. 15. Concrete 
sizes and amount of reinforcement required for joists 
and beams of various spans and supporting given loads 
may be determined by simple standardized calculations. 

Framing plans also contain—usually in general notes 
—data on design, detailing and placing, such as live 
load assumed, thickness of concrete outside the rein- 
forcement, bar chairs, points of bending, types of hooks, 
transverse reinforcement (temperature steel), type of 
slab cores or forms, quality of concrete, and grade of 
reinforcement. 


FOOTING SCHEDULE 


FOOTING eee HORIZ. BARS] YE VERTICAL 
=a ;EACH WAY DOWELS 


Ey 
El A 
EE [NS aR | es | ee | yee | 


BEAM SenEDU EE 


BEAM [DIMENSIONS |LONGIT. BARS [PRONG 
MARK its [oT fst [oem a, NOTES | 


set ft} | —— 
8-103 eit Ca LE 


TOP OF FOOTINGS 


FIG. 15. Design data on concrete construction may, in the simplest manner, be 
conveyed to detailer and builder by schedules and by typical details as indicated. 


17. WALL CONSTRUCTION 


Below ground level, walls should always be of con- 
crete, as illustrated in Fig. 16 which shows an interior 
and an exterior concrete wall with typical footings, as 
well as an areaway built around a window in the 
exterior wall. No waterproofing need be applied to the 
concrete, but two precautions must be observed to keep 
the basement dry—the concrete must be mixed* with 
as little water as is consistent with good workability 
for placing, and the fill adjacent to the wall must be 
properly drained. 

*Free copies of booklet on Design and Control of Concrete Mixtures 


are available in U. S. and Canada by request to Portland Cement 
Association. 


B°CONC. MASONRY 


A’BRICK FACING 


Low bid on Dothan, 
Ala., high school 
was $40,000 under 
the appropriation, 
which allowed the 
architect, Charles H. 
McCauley of Bir- 
mingham, to increase 
the size of the build- 
ing materially. 


There are many points in favor of using, above 
ground, a skeleton of concrete columns and beams in 
both interior and exterior walls. Speed of erection is one 
advantage, and changes in classroom layout as well as 
extension of the building are carried out with more ease 
and less cost when walls and partitions carry nothing 
but their own load. An outstanding advantage of skele- 
ton construction is its great lateral stability insuring 
safety against lateral loads due to windstorms and 
earthquakes. There is also economy in the first cost of- 
skeleton construction, as illustrated by a $42,000,000 
school construction program in Philadelphia about 


TERRAZZO FINISH IN CORRIDORS, LINOLEUM OR COMPOSITION 


wy Oe g's Ob, Seger a Perec. 


2° PIPE RAIL 


ANGLE SUPPORTING 
BRICK ABOVE WINDOW 
OPENING 


KOGHOOD IGA ER ELEEE SSN 


Teg ES oD ite oe, * 


: oe IN ees WOOD FLOOR ON SLEEPERS IN SSN 


REINFORCED CONCRETE 
DIMENSIONS & REINFORCEMENT 
TO BE SHOWN ON FRAMING PLAN 


ial UCOR 


SI ORE Gas = 
et a sanrigbuenh Oe Pes ie 


FIG. 16. Safety requires 
that heating and other 


REINF. CONG , a 
ious mechanical facilities, 
WALL eT 2-4 °CONTINUOUS . usually placed in base- 
4— 3°6-10" BOTHWAYS REINF. CONC. WALL eu ments, be completely 
¥ FEE : BOTH FACES FLOOR DRAIN ped a surrounded by concrete 
sone “=a CAULKING -5°CONC. SLAB 3 ?-10°'OC. BOTHWAYS BASEMENT fod construction. Ground 
9.3% 9 AGA PI IE A Se aS H on water should be properly 
4 a “CONST JOINT. CINDER ‘OR GRAVEL FIL FILL drained away from base- 
ore A ni PRECAST EARTH ¥ Ze ments 
CONC. BLOCK KEYS . 
G'DRAIN TILE r¢ oe © DRAIN TILE 
8 $12"O.C 3-4 CONTINUOUS 
SCALE % = 1:0" 


22 


VERTICALLY 
OUTSIDE FACE 


Yg"o- GO.G. 
HORIZONTALLY 


OUTSIDE FACE 


ee 
Secgee 
Seert 


NOTE: EXTEND BARS AROUND OPENINGS 24" BEYOND SIDES OF OPENINGS. 2" PROTECTIVE COVER OVER 


BARS AT OUTSIDE FACE. 


FOR 10" WALLS USE 3/a"-10"0.C. IN BOTH FACES HORIZONTALLY AND %"¢-12"0.C. VERTICALLY. 


PROVIDE 2-%"¢ ON ALL SIDES OF OPENINGS. 


FIG. 17. Sketch indicates reinforcement to be placed in exterior walls of concrete. The use of concrete in 
exterior walls offers great opportunities for individual expression, as illustrated in some of the photographs. 


which Virgil L. Johnson says.* 


“Standardized specifications and standardized 
building methods, particularly the adoption of 
the concrete skeleton type of construction, have 
brought about a saving of $3,500,000.” 


Walls with 4-in. brick facing backed up with concrete 
masonry are illustrated in several of the line drawings. 
For the layout in Fig. 6, exterior walls of reinforced con- 
crete are sketched in Fig. 17 which shows typical rein- 
forcement recommended. Large-scale details of opening 
for window sash of either steel or wood are given in Fig. 
18. Data on designing, making and erection of formwork 
for this type of construction are presented in a booklet 
Forms for Architectural Concrete**. 

In cold climates, exterior concrete walls may be insu- 
lated as illustrated in either Fig. 18 or Fig. 19. A }4-in. 
rigid insulation board with plaster is separated from the 
wall in Fig. 19 by blocking fastened to wood blocks cast 
in the concrete. This construction is effective and 
economical. In many instances, it will be fully satis- 
factory to omit the insulation board, or even to leave the 
concrete walls exposed and painted in the classrooms. 

The use of architectural concrete in exterior walls is 
especially attractive in schools because it offers the 
architect opportunity to mold and treat the concrete 
surface and thereby to put his stamp of individuality 
upon an otherwise thoroughly standardized building.*** 


*An Achievement in School Construction, see Reference No. 8. 

**Free copies available in U. S. and Canada by request to Portland 
Cement Association. 

***For illustrations of outstanding examples of buildings with ex- 
terior walls of architectural concrete, write to Portland Cement 
Association. 


SILL dante. | SILL 


FIG. 18. Details around window openings in walls of con- 
crete. Sash of wood or steel may be used, and the “‘awn- 
ing” type of window is often preferred because it provides 
the greatest unobstructed opening for ventilation. 


23 


18. ROOF FRAMING 


Roofs are often built with sloping surface and with 
suspended ceiling, the space between roof and ceiling 
being used for pipes and flues. A considerable volume, 
however, may be wasted in such layouts, and the sus- 
pended ceiling is expensive. It is possible in many 
schools to economize by making such arrangements that 
the roof may be made truly level, the suspended ceiling 
omitted, and the underside of the roof construction 


exposed in the classroom ceiling as discussed in 
Section 15. 

The framing described in this section is laid out for 
the roof over the two-teacher school for which the floor 
plan is shown in Fig. 22; but it applies also, with minor 
modifications, to the roof over the one-teacher school in 
Fig. 21, as well as to roofs over typical urban schools. 

As illustrated in Figs. 19 and 20, the roof over the 
classroom consists of a 4-in. thick concrete slab cast 


without slope, having insu- 
lation and waterproofing, 


A" 


SOLID CONC.SLA 
3°>-67"OC. ALT. BEN 


(S-) 


* ’ " | 
8 b 9-10 ae ; Ll. 

: | 

| 

| | 
FIG. 19. Concrete roofs laid SLAB A SLABA : SLABA | SLAB i 
aos 

i 


and with beams exposed in 
the ceiling below are good 
standard construction. Such 
level roofs may, in con- 
gested areas, be used for 
recreational purposes. For 
cross sections, sez Fig. 20. 
See Fig. 18 for detail of wall 
furred without use of the 
rigid insulation board. 


Perr: Sd eo eee 
ee eee 


ee 


BEAM A 


ROOF FRAMING PLAN 
SCALE-3"= 1-0" 


GUTTER fll 


BLOCKING CONTINUOUS 


\ 


S 
: 


Or 
<x = 
— Ly 
na ‘ 
Or 
aye 
z =< 
SOO = 
aA ad — 
ars 
Se) 


tA 
oe 
res 


CONCRETE 
SLAB 


INSULATION 
BLOCKING 


DETAILS AT JUNCTION OF WALL AND ROOF 


24 


SCALE -l3° = 1-0" 


integrally with and supported by two concrete beams 
at approximately the third-points of the classroom. 
The detail shown for the junction of wall and roof 
shows plaster and insulation board attached to the 
inside of the wall by means of blocking. The roof has 
rigid insulation boards laid on top of the concrete slab, 
the insulation being covered with composition roofing. 
In regions with frequent snowfalls, it may be preferable 
to omit parapets and to use gutters as illustrated. A 
better appearance is created, however, when the gutter 


9-10" 


is omitted; a low parapet may then be built in form of a 
6-in. high curb around the outside of the roof, or a 
parapet of standard height may be constructed. 


The roof slab in Fig. 19 is designed for the following 
loads: 


Live load = 30 p.s.f. 
Roofing and insulation board = 15 p.s.f. 
Concrete slab: 4 in. thick = 50 p.s.f. 

95 p.s.f. 


Tesoro O.C.ALT. BARS BENT 


TRANS. BARS 2"4-15"O.C.1N ALL ROOF SLABS 


10-6" 


TOP OF FIN. FLOOR 


BENT BARS IN EXT. SPAN 


PONE ERED 2) 


on = Se 


= aE 


e 
+ 8 
as 
Lo 
0 
4 


9-@" 


43° HORIZ.& CONT 
peries- Orc! 


TYPICAL SECTION 
THROUGH 
SPANDREL BEAM 


SCALE 321-0" 


3">- “55 "O.C. bevel 
ALT. BARS BENT 


VARIES 


ES, 


“Pasaay MARKED A 


a 

4 | 

gsxp VENT OPENING 
: 7 


ap 2-2 “¢ CONTINUOUS 
Pe eries- -12"0.C. 


¥| Se BelteceiN icine BENT SLAB B a 28 '# CONTINUOUS 


CENTER LINE 
2"> HORIZ. ENG 
2-FosTR ee 


SECTIONS IOI 


SCALE 4 21-0" 


BENT BARS IN INT. SPAW 


IBAR ues c 


—— 


4-1"¢ BARS 


IN BEAMS 


BEAM A 22-4" 


SECIIQN I 


SCALE "= 1'0" 


ne 
$7670. 


TOP OF FIN. FLOOR 


ZB eTIES-12"0.C. 


FOR HORIZ. BARS SEE SEC.I-1 


| ¢TOP OF FIN. FLOOR 


FIG. 20. Two-level roofs for rural schools reduce the building volume, improve appearance and provide better cross- 
ventilation in the classroom. Typical details shown correspond to floor layout in Fig. 22. For framing plan, see Fig. 19. 


25 


Maximum moment, M, in the slab for this loading 
is: 


1 
[-xterior span: i xX 95 X 10.02 X 12 = 10,400 in. lb. 


10,500 in. Ib. 


1 
Interior span: Tr x 1955x010. 525 xe 12 


With a total depth of 4 in., an effective depth of d 
= 4.0 — 1.0 = 3.0 in., the reinforcement required is: 
eu ae 10,500 
~ gdf, 0.875 X 3.0 X 20,000 

Use 3%-in. rd. bars at 614 in. o. c. and bend alternate 
bars. 

The load in |b. per lin. ft. on the beams is: 

Slab tiel a <g05 1050 
Beam: 1.33 K 150 = 200 
w = 1250 
When the beam is 12 in. wide (b), 20 in. deep, the 


effective depth is 20 — 2 = 18 in. (d), and the clear 
distance from wall to wall is l’ = 22 ft. 4 in., the maxi- 


A, = 0.20 sq. in. 


mum unit shear is: 
Yul’ 0.5 X 22.33 * 1250 


pg ZO Be A ee 
0 bid 12 X 0.875 X 18 ee: 


The longitudinal reinforcement required is: 


LYyul? 14X 1250 X 23.02 12 d 
A,=— a A 
jdf, 0.875 X18 X 20,000 


Use four 1-in. rd. bars, two straight and two bent. 

These bars and also wall reinforcement recommended 
for the rural schools shown in Figs. 21 and 22 are indi- 
cated in Fig. 20. Floor plans for these schools will be 
discussed in Sections 19 and 20. 

For a rural school with 22 ft. wide classrooms, stand- 
ard height from floor surface is 11 ft. to soffit of spandrel 
and 12 ft.to bottom of the concrete slab. It is unneces- 
sary to extend the 12-ft. story height to the auxiliary 
rooms, where 8-ft. clear height is sufficient. It is seen 
that the concrete roof construction laid out in Figs. 19 
and 20 gives the smallest possible building volume and 
yet provides all the space usually required for the 
school activities. 


D. RURAL SCHOOLHOUSES 


19. ONE-TEACHER SCHOOLHOUSE 


It is inadvisable to advocate using one floor plan for 
all schoolhouses of the same type regardless of differ- 
ence in local requirements. The purpose in presenting 
the floor plans in Figs. 21 and 22 is to illustrate prevail- 
ing features and to discuss governing principles. 

The one-teacher schoolhouse in Fig. 21, suitable for a 
maximum of 40 pupils, has a 22x32x12 ft. classroom. 
Desks for 30 smaller pupils and seats for 10 larger 
pupils are provided. Various classroom features have 
already been discussed in Sections 6 (Regular Class- 
rooms), 7 (Seating in Classrooms), 15 (Floor Framing) 
and 18 (Roof Framing). This school must be oriented so 
that the classroom faces in the general direction of east 
or west and is turned away from the road. The extra 
door in the classroom leads directly to the playground. 


The wardrobes as laid out in the classroom represent 
a departure from traditional rural school plans, which 
with few exceptions have coatrooms with toilets, one 
for boys and one for girls. The arguments that combine 
in favor of abandoning the use of such coatrooms are as 
follows: (1) coatrooms occupy considerable space, and 
cubage may be greatly reduced by using wardrobes 
utilizing the inner aisle in classrooms for service space; 
(2) small children are likely to be pushed around by 
larger pupils in coatrooms but may be kept separated 
in the classrooms where they are under direct super- 
vision; (3) the odor from the toilets in coatrooms may be 


26 


obnoxious and unappetizing for the storage of lunches; 
(4) undue confusion and crowding during recess may be 
created when pupils in moving from desks to play- 
ground, or vice versa, must go to the coatrooms for 
their wraps. 


It was decided, while studying various floor plans for 
the school sketched, to eliminate coatrooms, to pro- 
vide toilets in an isolated yet accessible corner of the 
schoolhouse, and to recommend the use of wardrobes 
arranged as indicated in Fig. 21. 


Another departure from the usual layout for small 
rural schoolhouses is the placing of the heater in a 
separate room, where fuel is also stored. The size shown 
for heater room as well as kitchen may be adjusted to 
suit individual choice. It has not been thought neces- 
sary to provide teacher’s room and work room; but it 
may often be feasible to build a work bench in the front 
part of the fuel room, an arrangement that is desirable 
in so far as the source of noise is removed from the 
classroom as far as possible. 


Roof and exterior wall construction for this school- 
house are similar to that shown in Figs. 19 and 20. For 
partitions, painted concrete masonry is recommended. 
All floor finishes in the front portion of the building 
should be of concrete or terrazzo as illustrated in Fig. 9, 
but for the classroom, composition tile or linoleum on 
top of padding is recommended for floor finish. 


FIG. 21. Classroom for 40 pupils and auxiliary rooms occupy a total volume o: 


17,000 cu. ft. Note omission of coatrooms and the use of wardrobes for wraps. 


Roof framing and wall details are similar to those in Figs. 19 and 20. The perspec- 


tive illustrates the appearance of the schoolhouse as seen from the road. 


1 € 


aes 


LEGEND 


B.B.: Blackboard 
B.S.: Book Shelves 


C.: Closet 

T.: Table 

T.D. Teacher's Desk 
W.: Wardrobe 

F.: Fuel 

H.: Heater 


DESCRIPTION 
Size of Classroom: 22x32 Ft. 


Ceiling: exposed concrete, painted. 


Floor Finish: linoleum or composition tile in 
classroom, terrazzo or concrete in other 
rooms. 


Walls: architectural concrete shown with in- 
sulation and plaster, or exposed concrete 
without insulation but painted. 


Partitions: concrete masonry, painted. 
Floor Construction: concrete slab on fill. 


Roof Construction: reinforced concrete (see 
framing plan.) 


Clear Height to Bottom of Roof Slab: 12 ft. in 
classroom; 8 ft. in other rooms. 


27 


20. TWO-TEACHER SCHOOLHOUSE 


Two classrooms, each 22x32x12 ft., are provided in 
the typical floor plan in Fig. 22 showing a schoolhouse 
accommodating up to 80 pupils. For discussion of vari- 
ous details, refer to Section 19 and the sections men- 
tioned therein. 


According to individual preference, the length of room 
may be varied, usually between 28 and 32 ft.; the width 
should seldom be made less than 22 ft. nor more than 
23 ft. Large room sizes are preferable where increase in 
school enrollment is anticipated. 


The two classrooms are laid out with an intermediate 
partition which may be removed, by folding or rolling, 
so that both rooms may be joined into one large room, 
64 ft. 8 in. long. This arrangement is incorporated in 
many rural schoolhouses because the large room is usable 
for community meetings, and also because both rooms 
can conveniently be supervised by one teacher, as may 
be necessary in emergencies. The removable partition, 
of course, must be installed with blackboard on the side 
faced by pupils; likewise, the wardrobe should have 
blackboard attached to the front of doors. 

In the front portion of the school are two rooms, one 
of which is laid out as kitchen. The other may be used 
as teacher’s room or as reading room. The plan makes 
provision also for toilets for boys and girls, for supply 
cabinet and stairs down to the basement, where heater 
room and fuel supply are placed. It is preferable that 
work rooms be built separately at some distance from 
the main building to avoid disturbance due to noise. 

This two-teacher schoolhouse, if built on a north- 


28 


Painted cinder block 
masonry used for 
partitions (and back- 
up) gives a light and 
interesting texture 
desirable for class- 
room finish. Note 
the beams exposed 
in the ceiling. 


south road, may have classrooms facing either east or 
west; but if it is built on an east-west road, classroom 
windows should face either southeast or southwest; in 
either case, the windows should be turned away from 
the road. 


If funds are available, it is highly recommended to_ 
add to the layout in Fig. 22 an outdoor gymnasium, 
which may be built as follows: Imagine a roof the size of 
that shown in Figs. 19 and 20 over one classroom turned ° 
in its horizontal plane through an angle of 90 degrees 
and placed adjacent to the south wall of the two-room 
house shown. Build this roof at the regular roof level and 
support it on pilasters similar to those shown between 
the windows in classrooms, but omit walls and windows. 
Build also, at regular floor level, a concrete slab on 
fill (see Fig. 9). 

An outdoor gymnasium of this type will prove highly 
useful not only for play and lunch but also for shelter 
in inclement weather and for pupils waiting for school 
to open or for transportation home. Above all, it may 
easily be transformed into a third classroom by simply 
building up walls between the pilasters and placing a 
finish on top of the concrete floor. If built in this eco- 
nomical manner, the outdoor gymnasium becomes a 
natural step in adding a third room whenever required 
by an increase in school attendance. 


The layouts in Figs. 21 and 22 may be readily modi- 
fied to include a basement. If this is desired, refer to 
Fig. 16 for vertical section through typical basement 
and to Figs. 13 and 14 for suitable framing for floor 
over basement. 


FIG. 22. Rural school, with two classrooms separated by removable partition and 


accommodating 80 pupils, occupies a total volume of 31,500 cu. ft. For roof 
framing and details, see Figs. 19 and 20. See text for description of how this 
schoolhouse may be ‘extended to provide a third classroom. The perspective 
illustrates appearance with a parapet extending 2 ft. above the roof. A 6 in. high 


parapet is used in the perspective in Fig. 21. For explanation of legend and special 


features, see Fig. 21. 


aac UNIOR OEE 
| 
| 


rele 
i aS S| 


TEACHERS’ ROOM 
OR 
READING ROOM 


HEATER ROOM UNDER THIS PORTION 


29 


E. SCHOOL SITE AND OUTDOOR HEALTH AC iy Pili 


Fine grounds are a necessity for beautiful buildings, 
and relatively small expenditures for landscaping and 
playground facilities will make the investment in the 
building appear far more significant than if the school 
site is left barren and ugly. 

Far too little ground is generally provided for 
school sites. To meet modern standard requirements, 
the smallest school should have at least two acres for 
outdoor physical education, and five acres is preferred 
for a school enrollment of about 500 pupils. 

The building is placed on the site so as to give good 
illumination in classrooms, to provide for future exten- 
sion, to have adequate space for attractive landscaping, 
and to allow good access from street to building as well 
as from building to playground. Sidewalks around the 
building are seldom less than 8 ft. wide and are made 
from 12 to 15 ft. at entrances. For the sake of safety, 
steps are to be avoided where possible and sidewalks 
to be built with ramps having slopes up to 15 per cent. 
Driveways and parking areas, which are often incor- 
porated in the development of the site, may be built as 
described in detail in the booklet Concrete Pavement 
Manual,* which also covers other construction details 
of importance for improvement of school sites such as 
sidewalks, curbs and gutters. 

In cities, both a gymnasium and a playground must 


be provided to keep the pupils as physically fit as pos- 


*Free copies available in U. S. and Canada by request to Portland 
Cement Association. 

**For dimensioned layouts see, for example, Standards for Junior 
High School Buildings, Reference No. 17. 


sible. In many rural schools, however, the minimum 
requirements include a suitable outdoor area improved 
and equipped for play or for formal gymnastics. An out- 
door gymnasium, as that described in Section 20, de- 
serves far more consideration than it has been given in 
the past. 

On the ground set aside for games, fields or courts 
are laid out for regular baseball, playground ball, soccer, 
hockey, basketball, volleyball, tennis and handball.** 
For games like tennis, handball, shuffle board and hop 
scotch, a surfacing of concrete of a construction similar 
to that in Fig. 9 gives excellent service, and the perma- 
nent construction will in the long run be the least expen- 
sive. Lines suitable for the various games may be 
painted on the concrete, bands of special colored con- 
crete may be laid in the surface, or grooves as illustrated 
in the photograph below may be marked off before the 
concrete hardens. 


For the pupils not in actual play, ample space is 
usually provided near the school building. For such area, 
a concrete slab laid on firm, even, well-drained subgrade 
is preferred. 


Ample playground area and facilities for games, to- 
gether with attractive landscaping, are recommended 
highly by all school authorities. The comparatively 
small expenditures made for playground improvements 
are considered well spent because they help a great deal 
toward attaining the ideal of making the schoolhouse a 
center of community life. 


Concrete pavement 
marked off for games is 
a suitable and perma- 
nent improvement for 
playgrounds. Grooves 
as shown may be marked 
with templates, or bands 
of colored concrete may 
be inlaid in the surface. 


A desire to prevent a fire such as destroyed the previous school on this site, and to protect children from other 
hazards, prompted Architect J. E. Coyle to design the M. S. Cunningham School, Joliet, Ill., in reinforced concrete. 


F. INCIDENTAL COSTS 


The investment to be made in the school building 
itself often overshadows other expenditures which may 
be relatively small but, nevertheless, are of major im- 
portance for the proper functioning of the school plant. 
It is not uncommon to find instances in which school 
bonds voted for a certain project prove insufficient be- 
cause incidental costs have been overlooked. This situ- 
ation may cause considerable concern and embarrass- 
ment with the result that the expenditures needed to 
complete the plant are curtailed, equipment cheapened, 
playground and landscaping neglected. 

A systematic effort should always be made to antici- 
pate and provide for all the costs connected with pro- 
jected building programs. Besides the capital outlays 
for the usual building contracts, many other items must 
be included in the budget, such as the incidental costs 
given in the following list.* 


I. Bond Issue: 
Election costs, bonds, legal service. 


II. Educational Consultant: 
Building survey, building consultant. 


*Taken—with modifications—from Extra Costs and Incidental 
Costs in the Erection of School Buildings, see Reference No. 24. The 
original lists are very complete and comprehensive. 


III. Purchase of Site: 
Purchase price, title search and guarantee, 
boundary survey. 

IV. Development of site for building: 
Topographic survey, test borings. 

V.  Architecturaland Supervisory Service for Building: 
Architect’s fee, blueprints, building supervisor. 

VI. Letting of Building Contract: 
Advertising for bids. 

VII. Educational Equipment and Furniture: 
Architect’s fee, purchase price. 

VIII. Development of Grounds: 
Playgrounds, landscaping, architect’s fee, sur- 
veys, grading, shrubbing, walks, roads, fences, 
playground equipment. 

IX. Miscellaneous Expenses: 
Legal service, insurance of building during con- 
struction, dedication. 


During the erection of the building, extra costs are 
almost always encountered which have not been antici- 
pated. It makes for much less friction and considerably 
lower cost of such items, if the contractor is instructed 
to submit, in addition to the contract price, prices per 
unit of work of the nature included in the general con- 
struction. 


31 


1 


2. 


Wie 


12. 


13. 


15. 


16. 


LG 


Every effort has been made in this text to collect and correlate information available from 
all sources so as to express as nearly as possible that which is most generally thought of as 
modern standards or prevailing principles—especially as applied to small or medium-sized 
schools. It is not claimed, however, that statements made are immune from discussion, nor 
are they to be thought of as final. On the contrary, considering the rapid rate of progress in 
American school planning in recent years, much continued growth is to be anticipated in this 
field. At the present stage of development, the best that can be accomplished is to design educa- 
tional plants with a maximum of flexibility and to construct buildings that will endure. These 
two features will, in the highest degree, contribute to long-term economy in schoolhouse 


construction. 


G. BIBLIOGRAPHY 


The references listed below comprise some of the publications used in the preparation of the foregoing text. For more compre- 
hensive bibliographies, see References Nos. 2, 7, 9 (pp. 299-320) and 11 (pp. 521-534). 


. Packer, Paul C. Housing of High School Programs. Teachers 
College, Columbia University, New York, 1924. 

Fowlkes, John Guy. Bibliography on School Buildings. University 
of Wisconsin, Bureau of Educational Research, Bulletin 6, 1925. 

. Eicher, HuBert C. American School Architecture. Pennsylvania 
School Journal, December, 1925. 

. Strayer, George D. and Engelhardt, N. L. School Building Pro- 
grams. Teachers College, Columbia University, New York, 1927. 

. Morphet, Edgar L. The Measurement and Interpretation of School 
Building Utilization. Teachers College, Columbia University, 
New York, 1927. 

. Thomas, M. W. Public School Plumbing Equipment. Teachers 
College, Columbia University, New York, 1928. 

. Smith, Henry Lester and Chamberlain, Leo Martin. A Bibliog- 
raphy of School Buildings, Grounds and Equipment. School of 
Education, Bulletin 4, Indiana University, Bloomington, Ind., 
January, 1928. 

. Johnson, Virgil L. An Achievement in School Construction. School 
Board Journal, Vol. 76, 1928, pp. 60-67. 

. Moehlman, Arthur B. Public School Plant Program. Rand Mc- 
Nally & Company, Chicago, 1929. 

. Engelhardt, N. L. Planning High School Buildings for Better 

Utilization. Architectural Record, Vol. 69, 1929, pp. 276-287. 

Spain, Charles Lyle and Moehlman, Arthur B. and Frostic, Fred 
Watson. The Public Elementary School Plant. Rand McNally 
& Company, Chicago, 1930. 

Engelhardt, N. L., and Engelhardt, Fred. Planning School Build- 
ing Programs. Teachers College, Columbia University, New 
York, 1930. 

Dresslar, Fletcher B. and Pruett, Haskel. Rural Schoolhouses 
School Grounds, and Their Equipment. United States Depart- 
ment of the Interior, Bulletin 21, 1930. 

. Gould, John J. Structural Features of the Park-Presidio High 
School, San Francisco. The Architect and Engineer, Vol. 102— 
103, 1930, pp. 105-107. 

Byrne, Lee. Check List Materials for Public School Building Speci- 
fications. Teachers College, Columbia University, New York 
1931. 

Harrington, W. K. and Dobbin, C. E. School Buildings of Today 
and Tomorrow. Architectural Book Publishing Company, New 
York, 1931. 

Engelhardt, N. L. Standards for Junior High School Buildings 
Teachers College, Columbia University, New York, 1932. 


18. 


19. 


20. 


21. 


23. 


Q4.. 


26. 


2 


28. 


29. 


30. 


31. 


Calhoun, J. B. The Use of Multiple-Type Furniture to Secure a 
Higher Degree of Classroom Utilization. Proceedings, Tenth 
Annual Meeting, National Council on Schoolhouse Construc- 
tion, Milwaukee, Wis., 1932, pp. 73-75. 

Eckles, W. G. Room and Equipment Facilities for Science in the 
Small High School. Proceedings, Tenth Annual Meeting, 
National Council on Schoolhouse Construction, Milwaukee, 
Wis., 1932, pp. 75-86. 

Johnson, Virgil L. Shallow Concrete Floor Developed by Phila- 
delphia Schools. Engineering News-Record, Vol. 108, 1932, 
p. 390. 

Sahlstrom, John W. Some Code Controls of School Building Con- 
struction in American Cities. Teachers College, Columbia Uni- 
versity, New York, 1933. 


. Strayer, George D. and Engelhardt, N. L. Standards for Ele- 


mentary School Buildings. Teachers College, Columbia Univer- 
sity, New York, 1933. 

Lee, Chas. A. and Viles, N. E. Schoolhouse Planning and Con- 
struction. State of Missouri, Department of Education, Bulletin 
2, 1933. : 

Misner, Frank M. Extra Costs and Incidental Costs in the Erection 
of School Buildings. Teachers College, Columbia University, 
New York, 1934. 


. Carr, William G. Opportunities in School Modernization. A Survey 


of School Conditions and Prospects in School Construction. The 
Architectural Record, Vol. 78, 1935, pp. 201—2-4. 

Barrows, Alice. Functional Planning of Elementary School Buald- 
ings. U.S. Department of Interior, Office of Education Bulletin 
No. 19, 1936. Available through Superintendent of Documents, 
Washington, D.C. 

Sykes, Earl F. A Modern Bibliography of School Design; also other 
articles on school planning. The Architectural Record, Vol. 79 
June 1936. 

Several articles on school planning and related subjects. The 
Architectural Record, Vol. 81, April 1937 and Vol. 83, May 1938. 

Modern High School Plant Design and Design Data for Scholastic 
Units. The Architectural Record, Vol. 82, August 1939. 

Englehardt, N. L. and N. L., Jr. Planning the Community School. 
American Book Company, New York, 1940. 

Wynkoop, Frank. Advances in the Art of School-Room Daylighting. 
The Architectural Record, Vol. 98, July 1945. 


PORTLAND CEMENT ASSOCIATION 


A National Organization to Improve and Extend the Uses of Concrete 


33 WEST GRAND AVENUE 


Printed in U.S. A. 


CHICAGO10, ILLINOIS 


S5-Second Edition 


secnsoousissennenntlagicmso ae 


me 


ASSOCIATION 


ee 


of hospital 


6a Congies: passed The Hospital Survey these facilities, stimulated improvement 
* to assist the states in surveying standards, and are encouraging modern architectural 
design and construction practices: Although many hos- 
ted in the last few years, both 


and Construction Ac 
i health facilities and to help 
ds guthorized 


Since then fun 
p to 


r the Act have yaried U 


*n any one for health services: 


By encouraging a pro 


$150 million, 
project covering 9S much as two-thirds of the cost. 
To administer the Act states are divided into hospita of the people and W 
service areas designated as base, intermediate or rural, tals available smaller institutions, a coordinate 
depending upo population and distribution of communi hospital system can be established to give everyone equal 
ties. The ultimate goal is to provide each base area with access tO he best medical and hospital care 
g medical and teaching hospital center, each intermediate ThenUs Public Health Service has reviewed this 
area with a well-equipped hospital £ at least 100 beds, booklet and much of the information on arrangement of 
and each rural area with 4 smaller hospital designed and facilities '5 taken from its publications 
equipped to suit the needs and economy of the community This booklet is intended fo assist those engaged in 
The 100-bed hospital 's discussed 9 this booklet hospital design and construction 1" securing full benefit 
Response fo the program laid down In the Act has been from the use of structural and architectural concrete an 
gratifying: A\l states and territories have established concrete masonry: Typical examples and design details 
central agencies which ar responsible for hospital activi- are presented and suggestions are offered to illustrate 
ies have studied the needs for addi- the best application of these materials 
i * Public Law 725 (gist Congress): also called the Hill-Burton Act. 


ties. These agencie 


tional facilities, 


Front C 
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J. Fraz Jackson-Madi 
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mith, Inc. and Assocs ree General Hospi 
-, Memphis, pistes at Jackson, T : 
; A. R. Jessu , Tenn. 
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structural 
engineer; H 
; Harmon 
Construction Co., Oklah 
5 ahoma Cit 
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contractor. 


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and educati ssociation 
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marily designed to im esearch, the develop 
prove and ment of 
extend the new or im 
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Introduction Z 


UNS ae is more than just a building with rooms for 
patients. It houses a highly specialized service. Be- 
fore planning such a complex building, the anticipated 
services of the hospital must be carefully programmed. 
This program should include a list of all required facili- 
ties for study by the architect and heads of the hospital 
departments during the planning stage. The Hospital 
Facilities Division of the U.S. Public Health Service has 
prepared several publications to guide the allocation of 
area to various hospital functions. These include Design 
and Construction of General Hospitals,* Elements of the 
General Hospital—Revised edition** and Plans of Gen- 
eral Hospitals for the Coordinated Hospital System.*** 
These may be obtained from the various state hospital 
agencies or the U.S. Public Health Service, Washington, 
DC: 

Once the site is selected and the size and services of 
the hospital are agreed upon, close cooperation of all 
concerned with design is necessary to develop an efficient 
building layout. The present trend in hospital design is 
toward a compact, multistoried building. 

Because of its purpose, a hospital building must be as 
safe as possible. Concrete framework, walls and floors 
are not only fire resistive, but their rugged strength also 
offers protection from the effects of earthquakes, wind- 
storms and blasts. It is essential to minimize the danger 
of hospital fires by insisting on fire-resistive construction. 
Firesafety must extend over the lifetime of a hospital, but 
it begins in the designer’s office. 

Concrete masonry walls are well suited to hospital use. 
Their resistance to sound transmission is beneficial to the 
patient and improves the working conditions of the hos- 
pital staff. In administrative offices and other nonpatient 
areas where plastered walls are not required, a variety of 
interesting wall patterns may be obtained with exposed 
concrete block. An important function of hospital walls 
is the support of cabinets and sinks and the concealment 
of pipes and vent stacks. Concrete masonry partitions 
possess the necessary substance and strength and also 
provide space for conduits. 

A hospital differs from other building types in that its 
annual operations budget, including maintenance, will be 
approximately one-third to one-half of its original con- 
* The Modern Hospital Publishing Co., Inc., Chicago. 


** Reprinted from Hospitals, April 1952. 
*** Reprinted from Architectural Record, January 1948, 


struction cost.* This emphasizes the desirability of build- 
ing hospitals with materials that require the least main- 
tenance and have the longest life. Inferior construction is 
undesirable and uneconomical, and if sufficient funds are 
not available initially for the type of construction needed, 
it is preferable to build a smaller hospital and plan for 
future expansion. 

One of the most frequent questions concerning a con- 
templated hospital project is ‘“‘What will it cost?’ Un- 
fortunately, there is no simple answer. When working 
drawings and specifications have been prepared, a fairly 
definite cost figure can be established by obtaining bids 
from competent contractors. Up to this point, any cost 
figure is guesswork. 

An estimate of total cost based on the “‘cost per bed”’ 
method is unreliable for present day hospitals. The com- 
plexity of the modern hospital and the fact that the 
service performed by one hospital may be quite different 
from that of another precludes use of this method. 

However, even a rough idea regarding costs will be use- 
ful during preliminary discussions when a compromise 
must be reached between services needed and funds avail- 
able. Exclusively for aid in preliminary planning, the 
Hospital Facilities Division has presented a discussion 
of costs in How to Estimate the Cost of Hospital Con- 
struction,** from which the following is abstracted: 


To calculate the approximate cost of a hospital, 
first establish tentatively the number of beds and pre- 
pare an inventory of proposed services. Total net 
floor area can be estimated by means of area charts 
given in the publication Design and Construction of 
General Hospitals, while approximate gross area in- 
cluding walls and mechanical spaces may be found by 
multiplying the net area by the factor 1.14. Total ap- 
proximate cost is obtained by multiplying this gross 
area by the cost per square foot of a similar project 
in the general geographical area of the proposed 
hospital. 


Almost all of the design and construction details pre- 
sented in this booklet apply to hospitals of any size. 
However, the 100-bed hospital is considered wherever 
size or function are governing factors. 

* Design and Construction of General Hospitals. 


** Robert A. Cohen “Hospitals,” Journal of the American Hospital 
Association, March 1953. 


he drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which 
should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. 


Copyright 1954 by Portland Cement Association 


Fig. 1. The multistory, 100-bed general hospital provides medical facilities for intermediate hospital service areas having populations of at least 25,000. 
The entrance to the administration wing is in the stem of the T-shaped building, and faces north. 


1G. | illustrates a 100-bed hospital proposed by the 
U.S. Public Health Service to provide all services 
usually rendered in a general hospital. In plan the build- 
ing is T-shaped with a full basement. The first floor ex- 
tends into the stem of the T where principal administra- 
tive offices are located. Inpatients and visitors reach the 
service area containing lobby, stairs and elevators through 
an entrance corridor in the office area. 

The service area has five stories above the basement. 
The wing to the left of the service area has four stories 
and houses all nursing facilities. The first and second 
floors are for surgical patients, the third floor for mater- 
nity cases and the fourth floor for medical cases. The four 
floors of the nursing wing are essentially alike in room 


4 


and utility arrangement. 

In the wing to the right, the first floor extends ap- 
proximately 137 ft. from the service area, and houses 
laboratories, facilities for emergency patients and the 
outpatient department. The second floor is approxi- 
mately 90 ft. long and contains operating rooms and 
adjunct facilities. The third or top floor is 48 ft. long and 
is occupied principally by delivery rooms. 

The basement has service facilities for food, laundry 
and heat. 

Suggested detail layouts for the separate suites and 
units incorporated in the building are made available by 
the U.S. Public Health Service.* 


* Elements of the General Hospital—Revised edition. 


Fig. 2. The compact arrangement of wings and serv- 
ice areas of the 133-bed Smith County Hospital, 
Tyler, Texas, makes it convenient to operate and easy 
to maintain. This architectural concrete hospital was 
designed to carry another floor for future expansion 
to 200 beds. Shirley Simons and Sons, Tyler, archi- 
tects; Mullen and Powell, Dallas, structural engineers; 
Campbell and Kay, Tyler, general contractors. 


Fig. 3. Rooms of the surgical suite have terrazzo floor finishes and precast concrete 
wainscoting to aid in maintaining cleanliness. 


100-bed hospital requires at least one 
A minor and two major operating rooms, 
oo ce A a cystoscopic room, two scrub-up alcoves, 
two substerilizing rooms and a clean-up room. 
Fig. 3 shows part of the surgical section on 
the second floor in Fig. 1. This partial plan 
includes two major operating rooms separated 
by scrub-up and substerilizing rooms. 

To provide a clear width of 10 ft. 6 in. in 
the surgical corridor, the transverse clear 
distance between columns in the surgical wing 
is 10 ft. 10 in. as compared with 8 ft. 4 in. in 
the nursing wing. This increase in column 
spacing allows an area that handles large 
amounts of stretcher traffic to remain free 
from obstruction. 

Fig. 3 indicates the use of load-bearing 
architectural concrete walls to support floor 
and wall loads. In this scheme the sections 
of wall between windows serve as columns, 
and spandrels function as beams. The figure 
also shows the use of precast concrete 
wainscoting. Terrazzo floor finish, divided 


Precast 


CLEAN-UP 
ROOM 


Vision 


CORRIDOR 


+ 


SCRUB-UP 
SUB-STERILIZING 


SIA 
STORAGE into squares by metal strips, is indicated 


in the operating room and surgical corridor 
area. A discussion of terrazzo finish is given 
in the section on floor finishes, page 27. 


STORAGE 


a - 


the central corridor with the floor cantilevered 


Bedroo m Uni ts for a 100-Bed Hospital 


HE size of each of the four nursing units of the hos- 
VP pital shown in Fig. 1 depends largely on the number 
of patients that can be assigned to the nurse in charge, 
and on facilities provided for each unit. One unit usually 
consists of 25 beds plus facilities such as the nurses’ sta- 
tion, visitors’ room, utility room, linen 
closet, supply closet, floor pantry, toilets, bath 
and solarium. 

Patient accommodations include one-, two- 


to either side. This arrangement results in an 18-ft. col- 
umn spacing and allows beds to be equidistant from 
the windows. 

Each bedroom in Figs. 4 and 5 is furnished with 
dressers, lockers and cubicle curtains. 


EL 


and four-bed rooms to provide flexibility for 
grouping according to medical and surgical 
treatment. A typical bay consisting of 2 two- 
bed rooms arranged for a 41-ft. 10-in. build- 
ing width is shown in Fig. 4. Since the recom- 


CrOsReheleDaOnn 


mended clear width for one-bed and two-bed 


rooms is 11 ft. 6 in.,* this layout results in 
column spacings of 12 ft. 5 in. and 15 ft. 7 in., 
or a total length of 28 ft. for the entire unit. 
Other columns are similarly placed to satisfy 


space requirements, and the use of identical 


column spacing at either side of the corridor 
simplifies planning and construction. 


Another unit of 2 two-bed rooms designed 
for a building width of 39 ft. is shown in Fig. 
5. The structural frame in this case (see Fig. 7) 


involves two rows of columns spaced along 


BED ROOM |z 
ali ® 


* Elements of the General Hospital—Revised edition. 


iE 


CoOPRe hea Boake 


Fig. 4. Typical arrangement of 2 two-bed 
rooms per bay fer reinforced concrete column 
layout shown in Fig. 6a. 
Legend: B—Adijustable hospital bed 

C—Cubicle rod and curtain 

D—Built-in dresser 

L— Built-in locker 


P—Plumbing space 


q 


Fig. 5. Use of the modified reinforced concrete 
frame shown in Fig. 7b allows this arrangement 
of 1 two-bed room with private toilet per bay. 
Legend: B—Adijustable hospital bed 

C—Cubicle rod and curtain 

D— Built-in dresser 

L— Built-in locker 

P—Plumbing space 


‘Fi oor Fra min g é JS 


HE perspective views of Figs. 6 and 7 illustrate two 
types of structural framing. Fig. 6a shows a frame- 
work of reinforced concrete consisting of architectural 
concrete bearing walls and interior and exterior columns. 
A modified arrangement is seen in Fig. 7b where the 
floor cantilevers from interior beams and columns to 


Roof 


3rd Floor 


2nd Floor 


Ist Floor 


Basement 


a. PERSPECTIVE 


Fig. 6. Reinforced concrete structural frame consisting of exterior and interior columns, beams and bearing walls is shown here with a one-way ribbed 


concrete slab. 


Ay 
a= = 
_ i 

is Ee. 

L 4s 

= ll 

eat ial 

i | | 
ees | 


a, PLAN 


support the exterior wall. As shown in Fig. 5, this latter 
condition allows a convenient layout of patients’ rooms 
without disturbing a uniform column spacing and, in 
addition, the fenestration is unrestricted by the structural 
frame. Fig. 7b illustrates the use of a ribbed floor for this 
layout. 


_———— ey, 

’ i 

L | 

=) = i 

a Saree) (eee) ire 

ener Sma" 
Lo Fine a 

cw (Pa d 

Le) ean eal aes LR : 

SS ae 

JP oLeE | 

Re J} 

ae ae | ae cae ae 

Seas py ie p 

(Cot ae So aie Ib= ig 
i 41-10" a 
b, PLAN 


Roof 


3rd Floor 


2nd Floor 


Ist Floor 


Basement 


DAPERSPECTIVE 


Fig. 7. A ribbed concrete slab formed with metal pans is suitable for use with a modified framework having beams and interior columns supporting 


cantilevered exterior bays. 


ae 


"Concrete finish 


6'x 8'x 21" Concrete 
soffit-type filler unit 


Concrete joists 


Fig. 8. Concrete masonry units serve as filler block for cast-in-place joists 
and provide a flat ceiling for plastering or painting. 


Figs. 6b, 8, 9, 10, 11 and 12 illustrate reinforced con- 
crete floor types suitable for use with the framework of 
Fig. 6a. The selection of type will depend upon loading, 
span, desired freedom from obstruction, insulation and 
acoustical properties. The one-way ribbed slab (Fig. 6b) 
formed with metal pans is a light floor receiving rigidity 
from the deep ribs or joists. This construction is satisfac- 
tory for floors carrying live loads up to approximately 
100 psf although the 2- to 3-in. topping is not suited to 
the support of heavy concentrated loads. Economy results 
from removal and frequent re-use of the pans. 

Another type of ribbed slab (Fig. 8) employs hollow 


concrete block to fill spaces between joists. These block 
improve sound and heat insulation and provide a smooth 
undersurface to receive plaster. Joist width is easily 
varied, and the T-beam action of joists and topping im- 
proves strength and rigidity. Either plain or soffit-type 
filler block may be used. 

The slab-band floor shown in Fig. 9 is essentially a 
one-way slab utilizing wide, shallow bands in place of 
narrow, deep beams. The band serves as a beam span- 
ning between columns and is considered a haunch in 
design of the slab. As a result, the critical negative slab 
moment at the edge of the band is smaller than that 
existing at the face of a beam in the narrow-beam type 
floor. Because of its reduced depth, this band requires 
more longitudinal steel than the narrow, deep beam, 
but the total amount of reinforcement and volume of 


Fig. 9. A reinforced concrete 
frame with slab-band construc- 
tion is used for the hospital of 
the Medical College of the Uni- 
versity of South Carolina at 
Charleston, S.C. Hopkins, Baker 
and Gill, Florence, S.C., archi- 
tects; Watson and Hart, Greens- 
boro,N.C., engineers; M. B. Kahn, 
Columbia, S.C., contractor. 


Fig. 10. Two-way ribbed con- 
crete slab with concrete mason- 
ry filler block used in floors of 
Veterans Administration Hos- 
pital at Wilkes-Barre, Pa. Kelly 
and Gruzen, architects, with 
Isadore Rosenfield as consultant; 
Severud, Elstad, Krueger, en- 
gineers; Merritt-Chapman and 
Scott, Corp., general contractors. 
All are of New York City. 


PN 


Fig. 11. Flat plate floor construction provides a smooth ceil- 
ing in the Olympic Memorial Hospital at Port Angeles, Wash. 
Reduced cost results from simplified formwork. Ceiling is 
exposed concrete with two coats of portland cement 
base paint, G. C. Field, architect, Seattle; H. H. Johnson, 
engineer, Seattle; J. G. Watts Construction Co., contractor, 
Portland. 


» 


Fig. 12. Reinforcement and utility conduits are in place for 
a one-way solid slab floor of the Tipton County Memorial 
Hospital in Indiana. McGuire & Shook and Assocs., Indian- 
apolis, architects-engineers; W. R. Dunkin and Son, Inc., 
Anderson, Ind., contractor. 


concrete in the slab are reduced. 

Fig. 11 illustrates a flat plate floor consisting of a 
solid concrete slab of uniform thickness supported by 
columns of uniform cross-section. It is essentially a flat 
slab floor but is distinguished by the absence of drop 
panels and column capitals. It requires a minimum depth 
and reduces the height of columns, walls, stairs, ducts 
and elevator framing. The smooth underside of the slab 
aids the placing of mechanical equipment and the sim- 
plicity of formwork and shoring results in added economy. 

The undersides of flat plate and slab-band floors may 
be left exposed in areas where it is unnecessary to con- 
ceal mechanical equipment. 


Stor yH eights : 


TORY heights are determined by minimum ceiling 
heights required by building codes and by space 
requirements for mechanical equipment. 

In the hospital under consideration, floor-to-floor 
height is established at 11 ft. 0 in. to allow proper room 
height in the surgical suite. In Fig. 13 pan construction 
is suggested for floors of the nursing and surgical 
wings to allow enough space for recessed lighting 
fixtures and pipes. Recommended minimum ceiling 
height for the surgical unit is 9 ft. 6 in. while 9 ft. is con- 
sidered sufficient in nursing rooms. A ceiling height of 
8 ft. in corridors allows space for placement of mechan- 
ical ducts below the structural floor. An important con- 
sideration in establishing floor elevations is the selection 


24 Terrazzo finish 
2 Concrete topping 


Dp oe 


| Suspended 
°-? ill plaster ceiling 


Precast concrete 
wainscot 


Convector unit 


I" Insulation 
board 


‘Baseboard 
radiator unit 


Tile floor on errazzo finish 


concrete finish 


TYPICAL WALL SECTION 
OF SURGICAL UNIT 


TYPICAL WALL SECTION 
OF NURSING UNIT 
Fig. 13. Ceiling heights depend on building code requirements and on 


space needed for mechanical equipment. Concrete joist floors provide 
recesses for utilities. 


10 


Roofing & insulation 
(Concrete roof slab 


Cast-in-place 
parapet 


Metal gravel stop 


x Roofing & insulation Ho. 2 (eA 
» || \ Concrete roof slab A? ee aE 
ie ST = t sannnnoo0r. ZL: R A 2 - — 
Toe (Om apes ae 
J Dr | Suspended 
UJ! plaster ceiling 


DETAIL OF 
STEP-UP SLAB 


Metal window 
frame = 
o 
re) 
Cast-in-place 
sill concrete 
wainscot 
Plaster 
Tile floor on Terrazzo finish 
concrete finish 


TYPICAL WALL SECTION 
OF SURGICAL UNIT 


TYPICAL WALL SECTION 
OF NURSING UNIT 


Fig. 14. Detail of roof slab provides for varying ceiling heights where roof 
occurs at both sides of step-up. 


of inside clear heights conforming to 4-in. modular di- 
mensions of concrete masonry units. This prevents un- 
necessary cutting and results in rapid construction and 
neat appearance. Heights of door openings should be 
planned to use full- and half-size concrete masonry units. 

Fig. 14 suggests a detail for varying ceiling heights. In 
multistory hospitals similar to that shown in Fig. 1 suc- 
cessive stories of the north wing are stepped back so that 
the slab above the second floor operating rooms serves 
only as a roof slab. The step-up slab detail of Fig. 14 
could be used to raise the level of part of this roof without 
necessitating a change in the floor line of the entire third 
floor. It should be noted that such a step-up may affect 
future expansion requiring the use of this roof as a floor. 
However, this detail can be used successfully to vary the 
ceiling heights of one-story buildings. 


Concrete Floors on Fill 


‘| ee basement floor of the hospital shown in Fig. 1 
is supported on the subsoil. Some design and con- 
struction details for this floor are illustrated in Figs. 15, 
16 and 17. 

Before placing a concrete floor on excavated ground 
or subsoil, all loose and nonuniform top soil is removed 
and the subgrade compacted uniformly. Fill, if required, 
is built up in layers not over 6 in. deep, each layer being 
tamped thoroughly. Mechanical tamping equipment is 
convenient for large areas, handwork being used only 
where necessary. Care should be taken to provide a uni- 
form dense fill. 

For maximum density, subsoil material should be com- 
pacted at optimum moisture content. Although accurate 
tests may be required to determine this content, an esti- 
mate may be obtained at the job site by hand-molding 
soil samples containing different amounts of water. 
When too dry, the mold falls apart and when too wet, it 
becomes plastic or muddy. 

After all fill has been placed it is scarified, shaped, 
rolled and tamped. The subgrade must be moist when 
concrete is placed to prevent absorption of mixing water 
by the supporting soil. In dry weather it is often neces- 
sary to moisten the subgrade just before placing the 
concrete. 

Expansion joints are provided between the slab and 
walls, and between columns and footings to allow free- 
dom for movement caused by settlement and nonuni- 
form volume changes. A ¥-in. premolded joint filler 
separates the slab from the wall or interior columns as 
shown in Figs. 15 and 16. A layer of 15-lb. felt is placed 
on horizontal footing surfaces which support the slab and 
the felt is given a mop coat of bituminous material. 

A concrete slab supported by firm subsoil and pro- 
vided with contraction joints spaced 20 to 30 ft. apart 
may not need reinforcement except in special locations. 
However, cracks tend to develop at re-entrant angles of 
slab openings and may be minimized by placing rein- 
forcement adjacent to the openings. Two or three #4 
bars placed near the top of the slab as shown in Fig. 16 
are considered satisfactory. 

When cast integrally in large areas, concrete slabs on 
fill often develop shrinkage cracks as the concrete hard- 
ens and dries out. These cracks usually travel from 
column to column since the slab is weakened along these 
lines by the presence of the column openings. Cracks are 


Grade line 


Reinforced 
concrete floor 


Projected metal 
window frame 


Pilaster = 
r 9 
iw 


Plaster 


Reinforced concrete 
areaway wall 


LJoint filler 
4" Concrete slab 


Concrete wall 
designed as 
grade beam 


U Joint filler 


Concrete finish 


earth fill 5 Concrete slab 


Stone or gravel fill 
6" Drain tile 


TRO RT RR A RT OR 


¢ of pilaster footing 


Stone or gravel 
Waterproof felt 


Fig. 15. Typical areaway for large basement windows. Long areaways 
require concrete tie beams at approximately 20-ft. intervals. 


2 Joint filler 


"Concrete finish 
5"Concrete slab 


3-4 Bars 
around opening 


| 
¢ of pilaster 
footing 


Fig. 16. Basement floor consists of two concrete thicknesses separated by 


waterproof insulation. Premolded joint filler separates the slab from all 
walls and columns. 


1] 


unsightly and may be controlled by means of contraction 
joints preferably placed at column lines. 

Interior contraction joints have no premolded joint 
filler such as that used around walls and columns since 
the initial shrinkage of concrete exceeds any subsequent 
volume change caused by moisture and temperature 
variations. These joints permit the slab to separate when 
tension develops. Location of cracks may be controlled 
by inserting a concealed strip of metal, wood or joint 
filler at the bottom of the slab to reduce effective slab 
thickness. To make the cracks clean and inconspicuous, 
a groove is tooled at the top of the slab with edges 
rounded to a radius of not more than 14 in. Reinforce- 
ment, if any, should be cut at all contraction joints. 

There are two methods for finishing concrete floors. 
The entire thickness of floor may be cast at once or a 
separate finish may be cast later. In one-course construc- 
tion, the concrete is placed and the surface screeded and 
floated to the specified floor elevation. Final troweling 
is postponed until all water sheen has disappeared and 
the concrete is hard enough so that no mortar accumu- 
lates on the trowel and a ringing sound is produced as 
the trowel is drawn over the surface. This will give a 
smooth finish. 


In two-course construction a separate floor finish | in. 
thick is applied any time after the water sheen has dis- 
appeared from the base. If the base slab and finish are 
not placed the same day, coarse aggregate in the base 
slab should be exposed slightly by wire brushing the 
surface. Just before placing the top course, the base slab 
should be thoroughly moistened and a thin coat of neat 
cement grout broomed into the surface. It is important 
that the coarse aggregate in the finish course be right 
at the surface. Overworking the surface tends to push 
large aggregate particles down into the slab and to bring 
the cement paste to the surface, an undesirable condition 
from the viewpoint of wear resistance. For additional 
information, see the section on Concrete Floor Finishes,* 
page 27. 

The construction shown in Fig. 16 is recommended if 
the floor is to be insulated. Subsoil is leveled and com- 
pacted and a 3-in. concrete base is laid and brought to an 
even surface. The hardened surface is mopped with a 
bituminous material and waterproof insulation placed. 
The slab on top of the insulating material is constructed 
as if it were placed directly on the ground. 


The slab in Fig. 15 cannot withstand upward hydraulic 
pressure. To drain water. away from the soil under the 
basement slab and thereby relieve pressure which might 
develop during heavy rains, two lines of concrete drain 
tile are laid in cinder or gravel fill as shown. The joint at 
the inside of the wall may be calked with oakum and 
* A more complete treatment is given in Concrete Floor Finishes 

and Concrete Floors on Ground for Industrial Uses. Both publica- 


tions are available free in U. S. and Canada on request to Portland 
Cement Association. 


a 


Basement wall 
"Concrete finish 


Membrane waterproofing 
2° Concrete base 


Fig. 17. Basement floor, designed to resist hydrostatic pressure, functions 
as an inverted slab. 


sealed with a poured joint filler to prevent the entrance 
of water. In addition, a metal water stop may be incor- 
porated in the joint to prevent dampness or the infiltra- 
tion of groundwater. 

When the water table is above the level of the base- 
ment floor, an upward hydrostatic pressure is developed 
and the slab should be designed as an “‘inverted”’ floor 
slab as illustrated in Fig. 17. The additional depth of slab 
under the column serves the same purpose as the drop 
panel in flat slab construction. The enveloping waterproof 
membrane is protected under the basement by a 2-in. base 
course and at the side walls by two 44-in. coats of port- 
land cement plaster. 


Architectural Concrete Walls 


RCHITECTURAL concrete exposed in building walls 
differs from concrete used in building frames and 
floors mainly in that more care must be taken during its 
construction. Complete plans and specifications are essen- 
tial and quality construction is required throughout to 
produce results which are satisfactory structurally as well 
as architecturally. 

Cement should comply with specifications C-150 or 
C-175 of the American Society for Testing Materials for 
portland cement and should be delivered to the job in 
sacks showing the brand and name of the manufacturer. 

Fine aggregate is usually natural sand, but sand made 
of crushed stone is also used. The sand should be graded 
from fine to coarse with 95 per cent passing the No. 4 
sieve. To obtain a workable mix that will not “‘bleed,”’ 
between 15 and 30 per cent of the sand should pass a No. 
50 sieve, and from 3 to 8 per cent pass the No. 100 sieve. 


For the average job, 95 per cent of the coarse aggregate 
should pass a 114-in. sieve and should be graded uni- 
formly with not over 5 per cent passing the No. 4 sieve. 
There may be quite a variation from job to job, but once 
a grading is accepted for a certain building no variation 
greater than 10 per cent should be permitted in the 
amount passing any sieve. 

Mixing water must be clean and free from harmful 
amounts of alkalies, vegetable matter and other impurities. 
In storage, the cement must be kept dry and the aggre- 
gates clean. Reinforcement in architectural concrete 
walls is generally of intermediate grade new billet or rail 
steel complying with ASTM specifications. Reinforce- 
ment shown in Table 1, page 14, is for resisting stresses 
induced by shrinkage and normal changes in tempera- 
ture. If the wall is to serve as a structural frame for sup- 
port of floors in multistory buildings, additional rein- 


Fig. 18. St. Vincent’s College of Nursing, Los Angeles, Calif., illustrates contemporary architectural design in concrete. At the left the modern appear- 
ance is accentuated by contrasting smooth and ribbed concrete surfaces. Horizontal and vertical V-grooves, visible in the foreground below, form an 
interesting wall pattern. Austin, Field and Fry, Los Angeles, architects-engineers; James |. Barnes Construction Co., Santa Monica, contractor. 


wW 


Fig. 19. In the all-concrete Veterans Administration Hospital at Spokane, Wash., a slab-band floor was used by John Graham and Co. of Seattle, architect 
and engineer, and George Rasque and Son of Spokane, associate architects. Robert E. McKee Construction Co., Los Angeles, was general contractor. Design 


and construction were directed by the Corps of Engineers, Seattle District. 


forcement may be indicated by the structural analysis. 
Some parts of the wall may require more reinforce- 

ment than the minimum recommended in the table. The 

parapet, for example, should have about 50 per cent more 


TABLE 1 
Wall 
thick- Horizontal Vertical 
ness, in. reinforcement reinforcement 
6 #3 bars at 8-in. ctrs. #3 bars at 8-in. ctrs. 
in outside face of wall in outside face of wall 
8 #3 bars at 6-in. ctrs. #3 bars at 8-in. ctrs. 
in outside face of wall in outside face of wall 
10 #3 bars at 10-in. ctrs. #3 bars at 12-in. ctrs. 
in both faces of wall in both faces of wall 
12 #3 bars at 8-in. ctrs. #3 bars at 12-in. ctrs. 


14 


in both faces of wall 


in both faces of wall 


steel than shown plus two horizontal #5 bars placed 
continuously just below the top. 

A typical arrangement of wall reinforcement is shown 
above the grade beam in Fig. 20. This elevation is taken 
at the north wing of the 100-bed hospital of Fig. 1, and 
the areaway indicated is the same as that shown in Fig. 
15. One curtain of bars is used in 6- and 8-in. walls and 
two curtains in thicker walls. Vertical bars in the outside 
curtain are placed at a clear distance of 2 in. from the 
outside wall face, and horizontal bars are attached inside 
these verticals. This allows maximum space for placing 
of concrete at the face of the wall where good appearance 
is desired. Continuous bars are spliced a length suf- 
ficient to develop full strength, and all intersecting bars 
are tied securely. The outside curtain of reinforcement 
may be held in place by tying it back to the inside form, 
or by inserting temporary wood spacers between this 
steel and the outside form boards. 

Construction joints are placed at the head and sill of 


Control joint 


C of pilaster 
sees 


¢ of pilaster 
RIiPiscor 


Tie beam 


Reinforced 


‘ ner f 
Construction concrete floor 


joint— 


Plaster and 


furring 


Construction 


joint 


Lower part of 
concrete wall 


designed as 


grade beam 


Basement floor 


Control joint 


ELEVATION 


[ [ here | 
Bessie ih fa 


SECTION A-A 


Fig. 20. Arrangement of reinforcement for an architectural concrete wall adjoining the areaway in Fig. 15. Lower wall functions as a grade beam 


spanning between column footings. 


the window opening of Fig. 20 and a vertical control 
joint is placed at the center of the window with alternate 
horizontal bars stopped 2 in. clear on either side of the 
joint. 

Careful control of uniformity, density and workability 
of the concrete mix is of prime importance in architec- 
tural concrete work. Aggregates and cement should be 
measured by weight rather than by volume. In regions 
where freezing temperatures are rare, durability may be 
obtained with a mix containing not over 7 gal. of water 
per sack of cement and not less than 514 sacks of cement 
per cubic yard of concrete. Elsewhere, these limits must 
be changed to a maximum of 614 gal. and a minimum of 
SY, sacks. Slump should not exceed 6 in. for hand plac- 
ing but a 4-in. slump is better when the concrete is vi- 
brated in place. 

To avoid segregation and splashing, concrete for ex- 
posed walls is placed through a chute or ‘elephant 
trunk” made of canvas or metal. The concrete should 
be kept wet for at least 5 days to cure unless high-early- 
strength cement is used. In this case 2 days curing is 
satisfactory. 

Cleaning the wall is the last important operation. 


Burrs are ground off and oil spots removed with a 5- to 
10-per cent solution of muriatic acid. This solution must 
be thoroughly washed off. A grout consisting of one part 
portland cement, a portion of which is white cement, 
and one part fine sand is brushed on the concrete surface 
after it has been moistened. The amount of white cement 
used will vary depending on the color desired. This grout 
is floated with cork or other suitable floats, filling all 
holes and pits. The excess grout is removed with a 
sponge rubber float. After a short interval, the wall is 
rubbed vigorously with dry burlap to remove dried grout 
from the surface without removing it from the pits. 

Furring may be required at the inside surface of archi- 
tectural concrete walls in the North to minimize heat loss 
and prevent condensation. Furring may be attached by 
means of anchors or galvanized wire cast in the concrete 
or by studs set by a powder-driven fastening gun. 

The subject of formwork for architectural concrete 
walls is not considered within the scope of this booklet. 
For a complete discussion see Forms for Architectural 
Concrete.* 


* Available free in U. S. and Canada on request to the Portland 


Cement Association. 


15 


Fig. 21. Continuous windows 
and concrete canopies of the 
Olympic Memorial Hospital, 
Port Angeles, Wash., allow 
maximum and comfortable use 
of natural illumination. 


HE location of window openings in exterior walls 
Reece the appearance as well as the comfort of a 
hospital. Fenestration is interrelated to problems of 
heating, lighting and ventilation and must be developed 
to harmonize with the architectural treatment of the 
building. 

Natural lighting is desirable in patients’ rooms, sup- 
plemented artificially when necessary. Many patients 
prefer to have fresh air and sunlight admitted through 
the windows and their comfort is increased considerably 
if they are permitted an outside view from their beds. 
For optimum lighting and ventilation, the top of the 
window opening should be placed as near as possible to 
ceiling level. The nursing units, if it is possible, should 
be arranged to receive benefit of southern exposure, pre- 
vailing winds and maximum quiet. 

Figs. 22 and 23 illustrate architectural details for win- 
dows used in conjunction with plastered walls or precast 
concrete wainscot. In both cases a cast-in-place sill is 
used with a precast concrete stool, and jambs and heads 
are formed with grooves to receive the metal frame. This 
frame is fastened by metal clips or cement mortar and is 
calked at the outside to prevent leakage. Construction is 


16 


facilitated by the use of standard dressed lumber for 
forming all wall openings. For example, lumber of 8-in. 
nominal width is used without cutting to form openings 
in a 7¥4-in. thick wall. : 

Plaster and insulation may be placed directly against 
the inside wall face, or wood furring strips may be used 
as indicated in Fig. 22 by setting beveled wood strips or 
nailing blocks in the concrete at the time of casting. 

Canopies are often cantilevered from exterior hospital 
walls for protection from rain and direct sunlight. These 
may be individual units over certain doors and windows 
or continuous as shown in Fig. 21. Flat and sloped cano- 
pies made integral with the architectural concrete wall 
are shown in Fig. 24. 

A discussion of types of window sash, screening and 
curtaining is presented in Design and Construction of 
General Hospitals. Additional details are given in five 
information sheets, Windows, Doorways, Reveals, Span- 
drels and Canopies.* These publications contain design 
suggestions together with drawings and photographs of 
actual construction. 


* Available free in U. S. and Canada on request to the Portland 
Cement Association. 


Beveled wood strip 


set} in concrete 


Beveled wood strip 
set in, concrete Plaster 


— ——t 


Nailing block 
{ be 


+ mortar Calking Cement mortar 


Plaster 


Precast concrete 


oll | KA U7Dovetail anchor 
eal teres. | 


Wood ifurring strip | 


wainscot 
Nailing block | 
Sess 
avant mortar 
Calking Metal clip 
Plaster |Return 
‘— Ay 
JAMB | 
4 \ | 
t. | | 
Precast concrete stool Precast concrete |stool 


Precast concrete 
wainscot 


ARCHITECTURAL ARCHITECTURAL 


t t t 
PROJECTED WINDOW 
WITH WAINSCOT 


| r z 
role ee iP Oe} PROJECTED WinDow Construction 
fe jill}e" 1 ET WITH PLASTERED WALL joint 


Fig. 23. Window details for an architectural concrete wall in 
the surgical area showing use of precast concrete wainscot. 


Fig. 22. Typical datails at window opsnings in nursing area. 


att | Eee a one ek 
a POREE ome: . Or af ey a ee ane oS ees pe er Oh eee ee fhe 
Beas Window aN ri Drip Window ate 
SLOPED CANOPY FLAT CANOPY 


Fig. 24. Canopies integral with architectural concrete walls afford protection from rain and direct sunlight. 


SECTIONAL VIEW OF STAIRWAY 


SIS : : at — es 


2 EN CE 
2 


SI} 


PLAN 


Fig. 25. Either cast-in-place concrete or concrete 
masonry walls may enclose the stairwell. A solid 
balustrade gives a feeling of security. 


eal 
‘| | 
| 
| | 
a 
“TH 
| | 
al 
| | 
a 
ail 
| 
i 
fl 


TAIRS and exits should be located so that walking dis- 

tance to the nearest exit from doors of private rooms 

or beds in open wards does not exceed 100 ft. In buildings 

with automatic sprinklers this distance may be increased 

to 150 ft. At least two exits should be provided as remote 

from each other as practicable. The clear width of stairs 
and landings should be not less than 44 in. 

The usual rules for dimensioning risers and treads are: 

1. Sum of one tread and two risers to be not less than 

24 in. nor more than 25 in. 

Qe Nosriser torcxceeday a1 

3. No tread to be less than 9 in. 

Stairs designed accordingly have been found adequate, 
safe and practical. People are accustomed to such steps 
and use them with comfort and convenience. Winders 
are not allowed. 

Openings are not permitted in the stairway enclosure 
except for access and light, and the stair structure and 
enclosing walls should be of incombustible material 
having at least a two-hour fire rating. This rating may be 
obtained with solid concrete or concrete masonry wall 
construction. 

Fig. 25 includes sectional and plan views of a typical 
hospital stairway. The inclined concrete stair slab is 
designed as a one-way slab supported by beams as shown. 


18 


The landing may be suspended by hangers from the floor 
above, supported on concrete struts from the floor below, 
or may bear on the enclosing walls. A live load of 100 
psf is satisfactory for stair design. 

Self-closing doors between corridor and stairway 
should open onto the landing, but enough space must be 
provided on the landing to avoid obstruction to traffic 
when doors are open. Continuous and smooth handrails 
are required on both sides of the stairs and a solid 
balustrade alongside the steps will give a feeling of 
security to the patients. Exit stairs should discharge 
directly to the outside or to a safe interior area which 
connects directly to the outside. 

The stairway shown in Fig. 25 may be constructed in 
two operations, the rough slab first and the finish for 
treads and risers second. The finish course should be 
1 in. thick. 

Fig. 26 illustrates two types of stair finish. One is the 
two-course construction discussed above and the other 
a finish consisting of precast concrete units. It is advisable 
to provide a nonslip surface on stair treads by adding a 
metal nosing as shown or by incorporating special non- 
skid aggregates in the concrete of the treads. 

Elevators are desirable when patients’ beds or surgical 
and medical facilities are on more than one floor. The 


Precast concrete 
Il Tread 


Concrete or terrazzo finish 
I" Tread 


%, 2. Liew - BS 
. Reinforced |. _. Reinforced |: 


“ concrete=-/« s-c-ess. .. concrete :| 


Fig. 26. Finish for stair treads and risers may be precast or cast in place, 
A metal nosing or nonskid aggregate in the treads gives added safety. 


100-bed hospital should be equipped with at least two 
elevators, one for passengers and one for service use. 
Passenger elevators should be located near the hospital 
entrance on the ground floor and in the vicinity of the 
nurses’ stations on upper floors to facilitate control of 
each floor by hospital personnel. 

Elevator cars should have a minimum size of 5 ft. 4 in. 
by 8 ft. 0 in. to hold a bed or stretcher and attendants. 
Doors should have an opening not less than 3 ft. 10 in. 
wide. 

Fig. 27 is a typical layout for stairs and elevators. With 
this arrangement it is advantageous to use architectural 
concrete walls (shown solid) to enclose the stairwell and 


SURGICAL 


Fm rn CS FATT OTR 


tH] 

a Spo | OD ES GENES OA PS CEA FSS OES TS 
Laundry chute ic 
5 H 


~ SS =a 
SS 
sae 
See | ee | 

aa oes 


joint 


Expansion 
ROOF joint 


ye 


Fig. 27. Plan of stair and elevator area at surgical floor. Walls shown 
solid are load-bearing cast-in-place concrete. Entrances to service and 
passenger elevators are generally separated. 


elevator shaft. These load-bearing walls eliminate the 
need for beams and columns in this area and also act as a 
shield against fire. The exposed walls require no painting 
or plastering and provide an attractive stairway. 

Information on requirements for stairways and other 
exits may be found in the Building Exits Code of the 
American Standards Association. 


Parapets, Copings and Roofing 


Seen. performance of parapets and copings 
can be achieved by proper attention to construction 
details and quality of material used. Concrete of the 
quality specified for architectural concrete walls should 
be used for parapets and copings. 

Tops of all walls are covered with a coping to eliminate 
the possibility of standing water. Cast-in-place copings 
should be sloped about °% in. per in. to insure quick and 
complete drainage. A steeper slope is hard to finish by 
troweling and involves the inconvenience of top forms. 
Steeper slopes on precast copings may be obtained by 
casting with the top surface down. 

If the coping is cast in place after the parapet concrete 
has hardened, the construction joint should be strong 
and tight. Laitance should be removed from the top of 
the wall and the joint surface roughened and brushed 


with neat cement grout before the coping is cast. In earth- 
quake regions, vertical reinforcement or dowels should 
extend into all copings. 

A projecting drip on the coping of an architectural con- 
crete building is not essential but may be used to direct 
runoff away from the wall, or as a decorative feature. 

Fig. 28 illustrates two parapets, one having a precast 
coping. A full mortar bed of 1:3 portland cement mor- 
tar should be used for bedding precast copings, and 
vertical joints between sections should be pointed with 
an elastic compound to a depth of about 34 in. The bal- 
ance of the joint is filled with mortar. 

Parapet stresses require more reinforcement above 
the roof line than in the wall below. This is particularly 
true at the coping. The details in Fig. 28 show recom- 
mended reinforcement. It is desirable to coat the entire 


19 


Fig. 28. Parapet walls may have precast or cast-in-place copings, sloped 
to drain off water. 


inside surface of parapets with roofer’s pitch, especially 
in regions where snow may drift above the flashing. 

No slope is necessary for drainage of flat roofs. If roofs 
are made level with drains, and overflows placed at least 
2 in. above the surface, a layer of water will cover the 
roof much of the time. This preserves the roofing and 


Tooled L Tooled edge 
edge, El LEI 
Construction |}: ’ -: Continuous P/.@ -x-“ 
aint! slot CT il hs 
Cement aie Sed en awe 
mortar Pao etl Pet eeoes 
sel.” eo. 
s re ae rj ie 
- ~|/Dowel ‘set | | -- | Bie, 
‘yin wall = =the ee 
[eae clllcumlliouan ee Calking 
“ff, b ae Cant strip 
eal “Ole L 
ee ya | eee: Roofing 
cn A eal Sc Insulation / 
2" Min lo" Minh fie fo Tn MITA ATA 
ie | ale io vale aN z ae fe 
Elevation Cast-in- Place Coping __|—Precast {Coping 


Fig. 29. Parapet detail for architectural concrete wall illustrating use of 
raggle and cant strip. 


helps in cooling the rooms below. At all vertical surfaces 
roofing should be flashed and counterflashed. When the 
parapet is cast in place, a raggle may be provided as 
shown in Fig. 29 and flashing is later calked in this 
groove. The height from surface of roof to raggle depends 
upon climate and precipitation. 


aa 


ONCRETE masonry has certain properties which make 
C its use desirable in hospital construction. Fire re- 
sistance, structural strength and the reduction in sound 
transmission offered by this material are essential in a 
building designed for the care of the sick. 

Advantage may be taken of the sound absorbing quali- 
ties of concrete masonry in nonpatient areas where ex- 
posed concrete block form the wall surfaces. A smooth, 
dense surface such as plaster absorbs about 3 per cent 
of the sound striking it but an exposed concrete masonry 
surface will absorb from 18 to 68 per cent depending 
upon the aggregates and surface texture. When plastered 
walls are required, concrete masonry adds to the com- 
fort of the patient by reducing the transmission of sound. 
Table 5 (page 16) of Concrete Masonry Handbook* gives 


* Available free in U. S. and Canada on request to the Portland 
Cement Association. 


20 


reduction factors in sound transmission through walls of 
various types of concrete masonry construction. 

Estimated fire-resistance ratings of hollow concrete 
masonry walls and partitions, as given in the National 
Building Code (1949) and recommended by the National 
Board of Fire Underwriters, are in the Concrete Masonry 
Handbook. These ratings are based on fire tests made by 
the Underwriters’ Laboratories, Inc.,the National Bureau 
of Standards and the Portland Cement Association, and 
indicate types of construction which satisfy various build- 
ing code requirements. 

ASTM specifications** require a minimum compres- 
sive strength for concrete masonry units based on gross 
area of 700 psi for load-bearing units used in walls pro- 
tected from frost action and 350 psi for non-load-bearing 


** American Society for Testing Materials’ Designation C90 and 
(CHS), 


STAFF 
LOUNGE 


CORRIDOR 


INFORMATION 


——1- 


2 CaSO a Se 
= ar* he es oo 
a Ce wees 
7 RGEC poy ae 
: vos Boece 


(ake re 


Fig. 30. Painted concrete masonry units laid in interesting and unusual patterns give a cheerful appearance to entrance lobbies. The photograph shows the 
wall pattern used in the Catawba Sanatorium, Roanoke County, Va. Brown, Wells & Meagher, Roanoke, architects; J. H. Saunders, Jr., Alexandria, associate 
architect; Fred Nicholas Severud, New York City, structural advisor; J. A. Jones Construction Co., Inc., Charlotte, N.C., general contractor. 


units. When units of 700-psi strength are laid in face 
shell mortar bedding using a 1:1:6 portland cement- 
lime, or stronger mortar, they produce a wall having a 
compressive strength of about 300 psi. The usual working 
compressive strength of 70 psi then gives a factor of safety 
of between 4 and 5 which is considered ample for mason- 
ry wall construction. 

Effective use may be made of exposed concrete block 
to create interesting wall patterns in nonpatient areas of 
the hospital. Some patterns that may be achieved are 
illustrated in Concrete Masonry Handbook, and Fig. 30 
suggests a treatment for the hospital entrance lobby. Pat- 
terns of this type are accentuated by tooling the joints. 

An attractive finish for exposed concrete masonry 
walls is obtained by application of portland cement paint. 
This paint is available in powdered form in a variety of 
colors, and is mixed with water before use. The surface 


to be painted must be clean and should be lightly mois- 
tened before painting to prevent absorption of mixing 
water needed for proper curing of the paint. Brushes with 
stiff fiber bristles not over 2 in. long are used to scrub the 
paint onto the wall and into surface pores, and the 
painted surface is then kept damp for at least 24 hours. 
Detailed information on this subject is contained in the 
publication, Suggested Specifications for Application of 
Portland Cement Paint.* 

Figs. 31 and 33 illustrate typical wall sections for parti- 
tions in corridors and surgical sections of the hospital. 
Walls in patient areas should be given a hard surface 
such as plaster, and walls of operating rooms must have 
a moisture-resistant wainscot to a minimum height of 5 
ft. Cast-stone wainscoting is available in many colors. It 


* Available free in U. S. and Canada on request to the Portland 
Cement Association. 


2] 


- 


Concrete 


Plaster 


| 
2"«8'x ie" 
Concrete 
masonry 
units 


Precast concrete 


lintel 
aes eee 


Metal door 
frame 


Head of Door 
plaster on one side 


Heap oF Door HEAD oF Door i 
| es 


Head of Door 
without plaste 


4 


6x8xI6" Concrete A 


8'x8xI6" Concrete 
masonry units 6% 8"x16" . Plaster 


+ = 
masonry units 


6x8xI6' Concrete 


masonry units Concrete 
| | masonry 
Wire units Wire 
t4yanchors anchors 
Plaster 
Precast = Precast 
Gee, fare concrete 4x8xl6" concrete 
4x8 xl6 Concrete wainscot Concrete wainscot sliilga 
masonry units Part Height | masonry Part Height 
plaster on one side units without plaster 
SecT, - PART HEIGHT SECT.” PART HEIGHT 
iS 
rk Precast concrete Precast concrete i 
wainscot & base wainscot 
Plaster | 
| ] aie 
Dowel Dowel 
| 
Masonry PARTITION Masonry PARTITION 
Top of slab WITH WAINSCOT ON WITH WAINSCOT ON 
ONE SIDE ONLY BOTH, SIDES 


Fig. 31. Interior wall between corridor and bedroom unit. Alternate details Fig. 33. Interior wall between corridor and operaling room. Alternate 
show concrete masonry at corridor side which is on the right. details shown on the right may be used in nonpatient service areas. 


Fig. 32. Walls of exposed concrete masonry painted in light colors are used in corridors and administrative offices of the Veterans Administration Westside 
Hospital 820 S. Damen, Chicago, Ill. Architectural design by the Veterans Administration; general contractor, J. L. Simmons Co., Inc., Chicago. 


Fig. 34. The attractive lobby of the Veterans Administration Research 
Hospital, Chicago, Ill., utilizes cast-stone wall surfaces and a terrazzo floor. 
Schmidt, Garden and Erikson, architects; W. E. O’Neil Construction Co. 
and Kenny Construction Co., contractors, all of Chicago. 


has an attractive durable surface that will withstand the 
scraping and bumping of portable equipment. In addi- 
tion, this surface is cleaned easily and provides water- 
tightness in areas such as substerilizing rooms where high 
humidity may occur. Exposed concrete masonry may be 
used above precast concrete wainscoting in lavatories in 
the hospital administrative area. 

A precast concrete wainscot is anchored to concrete 
masonry backing with noncorrodible wire of at least 
Yg-in. diameter. These wires are placed in holes drilled 
¥, in. deep in the end surface of each precast slab parallel 
to its face and the holes are filled with mortar. There 
should be at least three anchors for slabs from 2 sq.ft. 
to 4 sq.ft. in area, four anchors from 4 sq.ft. to 12 sq.ft., 
and at least six anchors from 12 sq.ft. to 20 sq.ft. Attach- 


Lead lined door 
and frame 
Lead insulated 
concrete block 


Fig. 35. Walls of hospital X-ray departments may be shielded with special 
lead-insulated concrete block. 


laster 
Sawed concrete ae | 


block 


Metal door Jamb to be lead lined 
frame with 


strut angles 


Detail of Exterior 
Corner | 


4'x8'xI6"Concrete |:| | 
masonry units Balle 
| ps alle 


Wood furring 


Lead headed nail | 


Epp fo : Lead insulated lath 


ica 
Jo] |] Lea 
Plaster aes a 
slat 2 
“lo pl 
ak v 
Detail of Interior 
Corner 
= 
Plaster 


ONRY PARTITION 
LEAD INSULATED 


Fig. 36. Walls of conventional concrete block and lead-insulated lath for 
use in X-ray areas. 


ment to the masonry wall is made by inserting the looped 
end of the wire anchor into a mortar joint or by bending 
it down into the core of a block. 

When wainscoting is required at both sides of a wall, 
the detail shown in Fig. 33 may be used. Here precast 
concrete lintels over openings are desirable if the wall is 
to be plastered above the wainscot, or a concrete lintel 
block may be used if this wall will be exposed. In either 
case, concrete masonry courses should coincide with the 
top of the door frame. 

Walls, floors and ceilings of X-ray departments must 
be properly shielded for staff protection from overex- 
posure to radiation. This may be obtained either by the 
use of lead-insulated concrete block (Fig. 35) or by lead- 


ZS 


Down 


4'x8"xI6" Concrete 
masony units 


Section of 
column at 


Metal lath wainscot level 


Metal corner bead 


Fig. 37. Detail at interior column showing masonry partition faced with 
precast concrete wainscot. 


insulated lath illustrated in Fig. 36. Special insulated block 
are available from several manufacturers. If necessary, 
lead sheeting may be placed in the floor slabs above and 
below the X-ray rooms at the time of casting. 

Fig. 37 is a horizontal section giving wall details at an 
interior column for the partition indicated in Fig. 31. 
Fig. 38a shows the intersection of a partition wall with 


4"x8'xl6" Concrete 
masonry units 


a.EXTERIOR COLUMN b. MULLION 


Fig. 38. Partition walls may intersect exterior walls at columns (a) as in 
the construction in Fig. 6a or at window mullions (b) in the framework in 
Fiat zee 


an exterior column as seen in Fig. 4, and Fig. 38b the 
junction of a partition wall with exterior fenestration 
shown in the bedroom plan of Fig. 5. 


construction Joints 


} | ee construction joints occur wherever cast- 
ing operations are stopped and the concrete allowed 
to harden before the next lift is placed. The location of 


Construction joints 


a Control ba as 


these joints affects progress of the work as well as appear- 
ance of the finished structure and should be determined 
by the architect and indicated on his plans. If construc- 


Fig. 39. Construction joints placed at head and sill 
of window openings are obscured by rustications. 
Control joints are spaced at intervals of 20 ft. or less. 


Rustications at 
construction joints 


— Seed = 


ail aero pak: 


24 


es bes oe | Se ep ee oe es ae | 


==—=——== 


pas lll 


1 


PE ease cece ech [= ee 
i of | 1 ipod (4 
at er aah be aaa oe eee eee Sea Lo ee 
| | | | | | | 
\ | | | | | | 
qos — — bt! tt a te tt to tt a ot SS 
Control joints 


tion joint location is left to the contractor, his selection 
should be submitted for the architect’s approval. 
Construction joints should be close enough so that 
concrete between them is placed conveniently in one 
day’s time, without hurried or careless workmanship. 
When panel forms are used, joints should be spaced so 
that panels reach from one joint to the next. This avoids 
the unsatisfactory appearance of intermediate joints and 
the possible difference in concrete texture above and 
below the joint. When forms are placed for the next lift, 
the outside form should fit tightly against the concrete 
below so that leakage will be negligible and wall surfaces 
at either side of the joint will be flush. This may be ac- 


complished by bolting the form against the hardened 
concrete. 

Joints may be concealed by taking advantage of archi- 
tectural detail such as rustications. In this way, joints may 
blend with the architectural treatment of the building and 
will not be conspicuous. 

Construction joints are shown for the 100-bed hospital 
in Fig. 39. They are placed at head and sill of all window 
openings, and are concealed in horizontal rustications 
between window openings. 

Joints in the stair and elevator tower may be formed 
as a %-in. V which will not detract from the desired 
massive effect of the solid architectural concrete wall. 


OLUME changes due to variations in moisture and 

temperature set up stresses of considerable magni- 
tude in an integral concrete structure because of restraint 
to free movement between component parts. Although 
cracking from these causes might be minimized by suf- 
ficient reinforcement, it is more practical and economical 
to allow cracks to develop at controlled locations. 

A control joint in an architectural concrete wall is 
similar to a dummy joint in a slab on fill; both represent 
weakened planes along which cracking may occur. These 
joints control cracking along clean, straight lines. In walls 
it is general practice to make a groove in the exposed 
surface at the weakened plane. 

A typical control joint detail is given in Fig. 40. A strip 
of wood or rubber is tacked vertically to the inside form 
sheathing. This strip remains in place. A narrow, vertical 
groove is formed on the exposed wall surface by fastening 
a wood strip to the form as shown. These outside grooves 
are generally 114 in. deep and as narrow as possible. 
After the concrete hardens and the wood strip is removed, 
the remaining groove is filled with a nonstaining, con- 
crete-colored calking compound serving as a water seal. 

Numerous ways have been devised for forming control 
joints. In all cases it is recommended that the combined 
depth of inside and outside grooves be not less than 2 in. 
and constitute not less than one-fifth of the wall thick- 
ness. 

The location of control joints varies with each job. In 
walls having frequent openings a spacing of 20 ft. is con- 
sidered maximum except at and below grade where a 
closer spacing is desirable. The spacing in walls without 
windows should not be more than 25 ft. and a joint within 
15 ft. of each corner is desirable. 


Fig. 39 indicates the location of vertical control joints 
in the typical 100-bed hospital structure. These joints are 
placed at window centerlines where possible. Where off- 
sets occur at the second and third floors, a control joint 
is placed to the right of the column since cracks are most 
likely to develop at this point. 

Control joints should be used in basement walls since 
nonuniform shrinkage takes place in a wall located both 
below and above ground level. Fig. 20 indicates a control 
joint in a grade beam extending between column foot- 
ings. This joint is lined up with a similar joint in the wall 


SS 


Notch strip 8'o.c. 
to permit nailing 


— 


| 
6d casing nails 


—- 
SSS 


Use this detail 
for all unexposed 
or plastered 

interior surfaces 


Cut every other 
bar here 


PLAN 


Fig. 40. Control joints should reduce the effective wall thickness at least 
one-fifth. 


25 


above the window openings. 

Control joints should begin at the top of the wall foot- 
ing and follow the exterior wall face to the top of the 
parapet, across the top of the parapet and down to the 
raggle strip. At the inside face, the joints should extend 
from floor to ceiling. It is not customary to provide con- 
trol joints in floors. 

Control joints must be planned for interior masonry 
walls as well as exterior architectural concrete walls. 


Joints should be placed at junctions of walls and columns 
and in walls weakened by openings. They also should be 
placed where nonbearing walls join other walls. Control 
joints in concrete masonry walls may be formed by laying 
a vertical mortar joint, raking the mortar out to a 34-in. 
depth and filling the remaining open joint with calking 
compound. 

Details of control joints in concrete masonry walls are 
given in Concrete Masonry Handbook. 


ee general purpose of expansion and control joints 
in reinforced concrete buildings is the same—to 
relieve stresses from volume changes resulting from 
variations in moisture content and temperature. In 
buildings of ordinary size, control joints are sufficient to 
handle these stresses, but expansion joints are often used 
when the building length exceeds 200 ft. 

To be effective, expansion joints should separate a 
building into two or more completely independent struc- 
tures. Joints should extend through foundation walls, 
but column footings need not be cut at a joint unless the 
columns are short and rigid. No reinforcement should 
pass through these joints. 

Joint location is generally dictated by structural con- 
siderations, with architectural treatment of walls at the 
joints developed accordingly. Figs. 27 and 41 indicate 
locations selected for the typical 100-bed hospital, the 
joints being placed at major changes of building mass 
where stress concentrations are likely to occur. Fig. 42 
illustrates details of the expansion joint in the corridor 
floor where sliding plates flush with the floor are pre- 
ferred. Fig. 43 shows the junction of the exterior wall 


Fig. 41. Expansion joints are placed at major changes of building mass. 
(See also Fig. 39.) 


NURSING UNITS 


ADMINISTRATION 


26 


x5" Brass cover plate % x!" Brass plate 


Screws tapped to angles 6'o.c. 


Steel anchors 38 a> 2 
welded to angles/ “— Baie Compressible filler 


I6 oz. Copper 


aie 
Fig. 42. Expansion joint in corridor floor provides a smooth surface with 
no obstruction to walking or rolling traffic. 


Fig. 43. Crimped metal water stops assure watertightness of expansion 
joints at exterior walls. 


Metal angle with bolts 
3" long 2°0'ac. 


Plaster 


Metal trim 
secured to 
concrete 


I6 oz, Copper 


with the elevator shaft while Fig. 44 suggests a method 
for joining a roof (right) with a vertical wall at an ex- 
pansion joint. Here, the suspended ceiling is supported 
by wire ties and runner channels and is also provided with 
a joint. 

Expansion joints should be simple and positive in 
action since failure to operate properly can result in 
damage to the building. There may be frequent move- 
ments back and forth in the joint. Water seals are usually 
crimped strips of 16-oz. metal securely anchored at both 
ends while remaining flexible in the joint. Details are 
shown in Fig. 43. 

Additional information may be obtained from the 
publications* Construction Joints, Control Joints, and 
Expansion Joints in Concrete Buildings. 


* Available free in U. S. and Canada on request to the Portland 
Cement Association. 


Fig. 44. Junction of low roof (right) with vertical wall 
provides a suitable location for expansion joints. 


SS Nailing block 
res 


EAC = mine 
_7 Sliding 
surface 


Metal to match 
interior trim 


Screws tapped to 
metal ground 


HE floor finish plays an important part in the success- 
ful operation of a hospital and should be economical, 
durable, impervious, fire resistant, skidproof and easy 
to keep clean. Concrete finishes fulfill these requirements 
when constructed according to proper specifications. 
A terrazzo finish is used where a decorative floor treat- 
ment is required. Terrazzo is produced by the use of con- 
crete mixtures containing marble chips or other colored 


Fig. 45. Terrazzo floors in operating rooms of the Veterans Adminis- 
tration Research Hospital, Chicago, Ill., use closely spaced dividing 
strips for electrical conductivity. Terrazzo is widely used in hospitals 
because it is easy to keep clean. 


aggregate. Additional aggregate is rolled into the fresh 
concrete when necessary so that 70 to 85 per cent of the 
floor area will consist of aggregate. Pigments may be 
added to produce a matrix of almost any desired color. 

There are two standard methods of laying a terrazzo 
floor. One is the bonded finish in which a neat cement 
grout is thoroughly broomed into the surface of the struc- 
tural slab after the slab is cleaned and moistened. The 


underbed is then spread uniformly with its surface be- 
tween 4 in. and 34 in. below the finished floor level. 

In the broken bond finish, the structural slab is covered 
first with a 14-in. thick layer of fine sand and then with 
tar paper. The underbed is spread uniformly on the paper 
and brought to a level surface between 4 in. and % in. 
below the finished floor. 

In both methods, dividing strips of brass or other suit- 
able material are installed while the underbed is in a 
semiplastic state, the top of the strips being at least %2 in. 
above the finished floor level. The terrazzo mix is placed 
in the spaces formed by the dividing strips and com- 
pacted by means of heavy rollers. The surface is floated 
and troweled level with the top of the metal strips. 

As soon as possible the concrete is covered with | in. 
of sand or other satisfactory covering and kept wet for 
at least 7 days for normal cement or 3 days for high- 
early-strength cement. When the terrazzo concrete has 
hardened enough to prevent dislodgement of aggregate 
particles, it is machine ground. The floor is kept wet 
during this grinding process. 

A grout of portland cement, water and pigment of the 
same kind and color as the matrix is then applied to the 
surface to fill all voids. The grouting coat is removed 
after 72 hours and the surface is given a final machine 
polish. 

Details and specifications for terrazzo floor construc- 


tion are given in Concrete Floor Finishes. (For floors on 
fill see page 11.) 

When concrete floors are to be covered with materials 
such as linoleum, rubber, cork or asphalt tile the struc- 
tural concrete is finished to an even surface slightly below 
finished floor elevation. The concrete should be thor- 
oughly dry before the covering is applied. Dryness may 
be checked by placing a piece of the covering on the 
concrete surface. If moisture appears on the underside 
of the covering material after 24 hours, the concrete 
should be allowed to dry further. 

Floor surfaces for specific hospital areas should be 
selected for durability, economy of maintenance, and 
utility. Linoleum or rubber vinyl or asphalt tile will 
provide comfort and resiliency for offices, patients’ 
rooms, treatment rooms, patients’ corridors, laboratories, 
workrooms and solariums. Bathrooms, toilets, showers, 
hydrotherapy rooms, utility rooms, serving kitchens and 
cafeterias usually have terrazzo floors. Operating, delivery 
and emergency suites should have electrically conductive 
floors of terrazzo.* Fig. 45 shows the use of terrazzo in a 
modern operating room. Terrazzo floors.also are suitable 
for public corridors, lobbies, stair halls and other areas 
used by the public. Coved baseboards are indispensable 
for all floor finishes. 


* See ““Low Cost Conductive Flooring for Hospitals,” pages 5-11 
of The Construction Specifier, July 1949. 


JT small hospital having 20 to 25 beds serves the basic 
need of a rural community that is too far from larger 
facilities to depend solely upon them. In this situation, 
limited finances usually require economical construction 
and maximum use of available space. 

The layout of the Decatur County Hospital at Oberlin, 
Kan., (Fig. 47) illustrates how facilities can be concen- 
trated and yet permit efficient hospital operation. An out- 
standing feature of this design is the double corridor that 
separates nursing units at either side of the building and 
provides common utility and storage rooms at the center. 
This arrangement shortens horizontal travel and improves 
working conditions for hospital personnel. The nurses’ 
station, focal point of hospital activities, is located at the 
intersection of the double corridor with the flow of traffic 
from the hospital entrance, a position that allows control 
of nursing units and visitors. The proximity of this station 


28 


to the business office and entrance lobby allows the nurse 
on night duty to maintain control in the absence of other 
employes. 

Operating and delivery rooms are located at one end 
of the building where there is no traffic other than that of 
ambulance patients. The central sterilizing department is 
next to the surgical suite and the nursery, closed off from 
the corridor, is close to both delivery room and maternity 
nursing units. Service facilities including kitchen, storage, 
laundry and utility room are isolated at the opposite end 
of the hospital and are provided with a separate corridor 
to avoid annoyance to patients. The kitchen is con- 
veniently related to nursing units for easy service of meals. 

The design shown in Fig. 47 involves concrete bearing 
walls, floors and roof. Subsurface construction included 
only wall footings and the mechanical equipment space 
shown in the transverse section of Fig. 48. Emphasis of 


Fig. 46. The Decatur County Hos- 
pital, Oberlin, Kan., illustrates con- 
temporary design of small hospi- 
tals of architectural concrete. 
Thomas W. Williamson & Co., 
Topeka, architects; O. D. Milligan 
Construction Co., Manhattan, 
contractor. 


horizontal lines and use of the roof overhang give a vertical and horizontal rustications in the architectural 
pleasing architectural appearance to the single-story concrete walls. Details of this rustication are given in 
structure. The contemporary treatment is accentuated by Fig. 49. 


PEAT joint - see di detail B _Fig. 50 


pee tl ~ Ses. Ee 


| +H == 

le io 2-BeD LE 2-8e0 |] 2-2e0 4 HT, -eco |2-eeo LH 2-20 | 1-ae0 al iT CENT 
| 4 | ROOM F 7 ROOM J ROOM "7 ROOM | ROOM tes ROOM STER 
a (ot iLL 

| 

| 

| 

| 


OPERATING 
ROOM 


ISOLATION -= 


ROOM nS NRS 
SPEANCe Fe] s [esfsrort | Ex | UTILITY | B [uinen [sr] J ean 


rm : 
— 


SERVICE 


a 
AMBULANCE 
ENTRANCE 


DELIVERY 
ROOM 


mana KITCHEN 


z |t40 Ly oe | no fl fo 
LAUNDRY | STORAGE ft = He 
Detail A Cy, z the, 
Bia 20) (FAG GGG Cao &b States =a eye a 
= ie e id 
WAITING 
ComonsO CO OGonD VEST 


ve 


SCALE IN FEET ae Pee oF 


1 O8aR apnure 


—————— Es 
O55) 10) 515) 20525 MAIN 


ENTRANCE 


Fig. 47. Use of the double corridor allows concentration of hospital facilities. Nurses’ station is placed for maximum control of visitors and patients. 


CORRIDOR} LINEN 


MECHANICAL EQUIPMENT 


Fig. 48 Transverse section 
of single-story hospital with 
partial basement. 


I0'-2" 


BED ROOM 


CORRIDOR BED ROOM 


29 


Fig. 49. Typical detail of hori- 
zontal rustication. Such grooves 
are often used at construction 
joints and become a conspicuous 
part of the architectural treat- 
ment, 


< 


West wall 


Metal water dam 
| du 


East gua 


DETAIL A 


DETAIL B 


Fig. 50. Metal water dams are used in the expansion joint (see Fig. 47) at 
the east (A) and west (B) faces of the building. 


Cast-in-place 
parapet 


“61 “Suspended 
“ol! plaster ceiling 


o.” |/Rustication 


. ac) 
sas 
, 
pon 
is 
ra 


Insulation board 


Metal double 
7-O" high © 
wainscot D 


fie: 


Rustication 


TYPICAL WALL SECTION 
OF SURGICAL UNIT 


TYPICAL WALL SECTION 
OF NURSING UNIT 


Fig. 51. Wall sections for one-story architectural concrete construction 
illustrate the roof overhang at patients’ rooms and increased ceiling 
height in surgical areas. 


30 


The building is separated into two parts by a transverse 
expansion joint shown in Fig. 47. The details of Fig. 50 
indicate metal water dams used at the exterior building 
faces between the kitchen and storage room (detail A) 
and at the west elevation (detail B). The expansion joint 
detail at the floor may be similar to that shown in Fig. 42. 

Typical wall sections for nursing and surgical units of 
a one-story hospital are shown in Fig. 51. Walls are cast 
in three lifts with rustications provided at the two hori- 
zontal construction joints. These joints coincide with the 
head and sill of all windows. The floor is supported by a 
compacted subgrade and is separated from the walls by 


Wood blocking 


Corner bead 


Metal window 
frame 


———— 


Optional concrete Plaster 


window frame — 


=a 


Furring 


Wood blocking 


is 
Corner bead 


Beveled edge J 
Calking 


Rustication —1— Precast concrete 


Optional cast- 


in-place sill DouBLE HUNG 


MeTAL WINDOW 


Fig. 52. The double-hung window is easily installed and made weather- 
tight in cast-in-place concrete walls. 


Fig. 53. Unusual design for hospital entrance features closely spaced horizontal grooves. 


an expansion joint filled with a bituminous material. The 
roof, consisting of a ribbed slab formed with metal pans, 
overhangs at the nursing units to give protection from 
sun and rain. 

Use of the double-hung window in architectural con- 
crete walls is illustrated in Figs. 51 and 52. Fig. 52 also 
shows the optional concrete window frame which, if used, 
is integral with the wall. Concrete window frames are 
visible in Fig. 46. 

Fig. 54 gives details of the ambulance entrance shown 
at the north end of the hospital in Fig. 47. In addition to 
the framework of the wall opening, entry walls and soffit 
were cast integrally with the architectural concrete wall. 

Many of the details described for the 100-bed hospital 
are applicable to both smaller and larger structures. The 
layout of hospitals of any size depends largely upon the 
bedroom unit, the arrangement of which determines the 
dimensions of nursing areas and may affect the structural 
frame layout but not necessarily the details. 

A hospital building should be functional but flexible 
for future expansion. For sturdiness and economy, rein- 
forced concrete construction is recommended. This com- 
bined with a restful, dignified architectural treatment both 
inside and out will provide a hospital which is an asset 
to the community. 


he 


; ea | 


Suspended 
ceiling 


Concrete * “}| |. 
= frame | /|3 


HALF ELEVATION SECTION 


Fig. 54. The ambulance entranceway is an integral part of the architec- 
tural concrete wall. 


31 


rH MER 


Printed in 


33 West Grand Avenue ° Chicago 10, Illinois S6—3M— 10-60 


oncrete Floor Finishes 


Se 


Portland Cement Association 
33 WEST GRAND AVENUE ¢ CHICAGO, ILLINOIS 


11 YEARS OF REAL PUNISHMENT—For 11 years this 
concrete floor has been used for heavy trucking at Tool 
Steel Gear and Pinion Co., Cincinnati, Ohio. The 
owner reports, ‘*... we find that it is holding up 100 
per cent...”’ 


OS hat 


AFTER 20 YEARS—This concrete floor in the truck- 
ing aisle of a paper storage room at Eastman Kodak 
Co., Rochester, N. Y. after 20 years is giving the 
same excellent service as when new. 


FOREWORD 


RCHITECTS and engineers want to specify and 

obtain the best concrete floor for a given type 

of service. The contractor’s desire is to build exactly 

what the plans and specifications call for. Certainly 

the owner is entitled to a floor that will meet the 
hard use any floor always receives. 

Within the covers of this booklet have been brought 
together the results of years of laboratory research 
on proper methods of making and placing concrete 
for floor use. These laboratory data have been proved 
on actual concrete floor construction and found to 
be reliable under service conditions whether for light 
or heavy duty. Special sections are devoted to the 
most ornamental and colorful of all floors—those of 
colored concrete. 

The information will tell the owner how to get 
what he needs—it will assist the architect and spec- 
ification writer in preparing their plans—it will show 
the contractor how to build serviceable and durable 


AFTER 25 YEARS—Millions of feet and thousands of concrete floors economically. 
loaded trucks have passed over this concrete floor of a plat- 
form at Grand Central Terminal in New York City since 


jchvastholltias Soureaent Portland Cement Association 


CUNCRETE FLOOR FINISHES 


Careful selection of materials! 
Skilled supervision! 
Workmanship! 


HESE are the ingredients of which good floor sur- 

faces are made! The “goodness” will be in direct pro- 
portion to the efforts expended by the architect, engineer 
and contractor in making certain that all three above 
essentials—not any one—are maintained throughout the 
construction of the whole job. The top surfaces of floors 
take the wear and grind. For that reason they deserve 
all the attention possible during construction. If this 


ER 25 YEARS—Trucks loaded with metal castings have been 
over this concrete trucking aisle in the plant of the Stanley 
Works at New Britain, Conn. for 25 years. 


is properly done, concrete floors will resist extremely 
severe conditions indefinitely and “‘dusting’”’—that most 
troublesome of floor diseases—will be unknown. Prop- 
erly made wearing surfaces is the subject of this book. 
The structural slab which carries the surface is dis- 
cussed only to the extent of showing its relation to the 
wearing course. Too often floors are specified to be given 
a “cement finish’’. Then follow inadequate requirements 
as to materials or procedure to be followed during con- 
struction. Then, the inevitable sequence—trouble. 
There are certain basic principles of concrete making 
which every user of concrete should understand. Because 
of the thinness of floor finish and the nature of its ser- 
vice, it is particularly important to observe these prin- 
ciples. A different manipulation or working of the 
concrete into place is used in making floor finishes than 
in other parts of the structure. It is important that 
directions for doing this be observed carefully. 


Fundamentals of Concrete Making 


Concrete can be made to have a wide range of quali- 
ties. Thus, the strength, resistance to wear, watertight- 
ness and other characteristics may be varied by changes 
in the materials or the proportions of the ingredients 
used and by differences in the manipulation of 
the concrete. 

The quality of the materials affects the quality of 
the concrete. Portland cement is made to meet standard 
specifications. It should be protected from moisture while 
in storage to prevent deterioration. Water used for mix- 
ing should be clean. Clean, hard, tough, suitably graded 
aggregates give more wear-resistant concrete than mate- 
rials which are inferior in these respects. 

The less water used in mixing concrete, the stronger, 
more wear-resistant and more watertight it will be, pro- 
viding the concrete can be placed properly. 

For uniform concrete, a mixture that does not permit 
segregation of the ingredients must be used. The pro- 
portions of the various sizes of aggregate and aggregate 
to cement and water should therefore be such as to pre- 
vent their separation during handling and placing. 

The chemical combination of cement and water to 
produce hard, strong concrete requires time. During 
this time moisture must be available, either by prevent- 
ing evaporation of the water used in mixing or by replac- 
ing that which does evaporate. 


e activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical 
rvice, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program 
tthe Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in 
e manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. 


COPYRIGHT 1957, BY PORTLAND CEMENT ASSOCIATION 


Applying these basic principles to concrete floor fin- 
ishes, the following requirements should be observed: 


1. Use only suitable materials. 


2. Use not more than 31% to 4 gal. of mixing water 
per sack of cement when machine floating is 
used and 41% to 5 gal. when floating is done 
by hand. These amounts include water intro- 
duced as surface moisture on the aggregates. 


3. Use mixtures and construction methods which 
will not permit segregation resulting in free 
water and fine material on the top surface. 


4. Prevent early evaporation of water by keeping 
the concrete wet as long as practicable. 


The aggregates constitute such a large proportion of 
the concrete volume and have so much influence in pro- 
ducing wear-resistance that they are of first importance. 


Aggregates for Floor Finish 


Since the aggregates in the wearing course are subject 
to abrasion, they should be of sufficient toughness and 
hardness to resist that abrasion. Where conditions are 
severe, traprock of a dense, fine-grained and interlocking 
crystalline structure or hard, fine-grained granites and 
quartzites are excellent. Where the duty imposed is not 
so severe, such as floors of a decorative nature, aggre- 
gates of less hardness may be selected. 

Aggregates may be either gravel or crushed stone. 
Materials containing a large proportion of elongated or 
thin fragments should never be used. All aggregates 
should be clean, free from dust or highly weathered 
fragments and should consist of particles which will not 
alter in physical or chemical nature in the presence of 
moisture. New and untried aggregates should be sub- 
jected to study before they are used in finishes intended 
for long service under severe conditions. 


Grading of Aggregates 


The grading or granular composition of the aggre- 
gates is equally as important as their hardness, shape 
and other characteristics. The fine aggregate or sand 
should consist chiefly of coarser grains ranging from 
to 14 in. in size. Not more than 5 per cent of the grains 
should pass a 100-mesh sieve, and not more than 15 
per cent should pass a 50-mesh sieve. Sand consisting 
chiefly of very fine particles should not be used. Stone- 
dust, clay and silt are particularly objectionable. Grad- 
ings of fine aggregates within the limits of the following 
table should give good results: 


Per Cent 
Passing’ *4-in, sievea 5. eee ae 100 
Passing No. 4 sieve . 95 to 100 
Passing No. 16 sieve. . 45 to 65 
Passing Nos o0sieverun eu eee een > LOM La 
Passing No 3100 sieve: ou ee LOM 


Coarse aggregate should be well graded pea gravel 
or crushed stone, the particles ranging between 14 and 
34 in. in size, with all particles passing a 14-in. sieve. 


4 


Gradings of coarse aggregates should be within the fol- 
lowing limits: 


Per Cenl 
Passing Y%-in. sieve ......... 100 
Passing 3%-in. sieve . . 95 to 100 
Passing No.4 sieve .. . . 40 to 60 
Passing No.8 sieve ......... Oto 5 


Artificial Aggregates 


Artificial aggregates made by heat treatment of cer- 
tain compounds in electric furnaces are sometimes used 
because they are hard, tough and produce non-slip sur- 
faces. Colored ceramic aggregates are available for ter- 
razzo. Artificial aggregates should be well graded and 
free from oil, grease and other harmful impurities. 
They should not be water-repellent. The directions of 
manufacturers should be followed. 


Mixes for Floor Finish 


The amount of mixing walter should be kept to a 
minimum. In no case should it exceed 4 gal. per sack of 
cement when floating is done by machine and 5 gal. 
when it is done by hand. The amount of surface mois- 
ture in the aggregates should be carefully determined 
and this amount subtracted from that specified. The 
exact proportions of the aggregates will vary somewhat 
with their gradings and are best determined by trial.* 
Experience has shown that with properly graded aggre- 
gates, satisfactory results will be obtained with propor- 
tions of 1 part of portland cement, 1 part of sand and 
from 11% to 2 parts of the coarse aggregate. 


Workahility of Concrete 


Concrete should be of such proportions and have such 
workability that it can be compacted and each aggre- 
gate particle becomes completely surrounded by cement- 
water paste, leaving no honeycomb nor voids. Floor 
topping is laid in a relatively thin layer and is compacted 
by tamping, rolling, floating and troweling. Therefore 
a stiff mixture can be used. Stiff mixtures are advanta- 
geous, as they permit less mixing water and more aggre- 
gate with a given amount of cement and prevent 
segregation of the materials. Such concrete is best mix- 
ed in the open top paddle type mixer. 

It is desirable to have as much as possible of the 
coarse aggregate near the surface of the floor to take 
the abrasion and wear of service. An excess of fine aggre- 
gate should therefore be avoided as it tends to work 
to the surface during compaction, thus defeating the 
purpose of the coarse material. On the other hand, the 
mix should not be too harsh for the methods of con- 
struction used. Harshness should be corrected by adjust- 
ment of the proportions of fine and coarse aggregate 
and the total amount of aggregate. The specified amount 
of mixing water should not be increased to produce 
workability. 


*The Portland Cement Association publishes the booklet Design 
and Control of Concrete Mixtures which explains proportioning 
by trial. This booklet may be had free of charge in the United 
States and Canada on request. 


Thickness of Floor Finish 


The wearing finish of concrete floors should be not 
less than 1 in. thick, whether it is placed at the same 
time as the structural slab or after the concrete in the 
structural slab has hardened. The thickness of structural 
slab will, of course, depend on design requirements. 


RECOMMENDED THICKNESS OF CONCRETE FLOOR 


FINISH 
Total thick- 
ness over 
structural Thick- 
slab, includ- | ness of 
Type of ing wearing | wearing Reinforce- 
construction finish finish ment 

Structural slab— 

bonded finish oe 1 in. 
Structural slab— 

integral finish ie: 1 in. 
Terrazzo— 

bonded 134 in. 5¢ in. 
Terrazzo— 

broken bond 21% in. 54 in. mA 
Over membrane 4x4-in. mesh 

waterproofing 3 in. 1 in. #8 gage wire 

4x4-in, mesh 

Over insulation 3 in. 1 in. #8 gage wire 
Resurfacing with- 

out removal of 4x4-in. mesh 

old finish 2 in. 1 in. #10 gage wire 
Resurfacing after 

removal of 

old finish 1 in. [Sine 


CONCRETE FLOORS FACILITATE HEAVY TRUCKING—At Trico Products Corporation in Buffalo, N. Y. zinc used in die casting is 
moved on trucks haying small steel wheels. Smooth-surfaced, wear-resistant concrete was chosen as the best flooring for these conditions. 


When floors are placed over a membrane waterproof- 
ing or over insulation, a reinforced slab at least 3 in. 
thick should be placed over the membrane or insulation. 
The top 1 in. may constitute the wearing finish. These 
recommendations and others discussed in this booklet 
are summarized in the accompanying table. 


Mechanical Floats and Special Methods 


Mechanical floating equipment is available which will 
compact and float mixtures that are much stiffer and 
harsher than can be finished by hand methods. When 
these mechanical floats are used, the mixture should be 
so stiff that when a sample is squeezed in the hand 
only a slight amount of moisture is brought to the 
surface. Thus mechanical floating has a great advantage 
over hand methods as the amount of mixing water re- 
quired for a given mix will be less by at least a gallon 
per sack of cement. 

In a patented method that has given satisfaction, a 
plastic mixture is used, but some of the excess water 
used for mixing is withdrawn before the cement sets. 
Before the wearing course hardens, it is covered with 
burlap over which is spread a thin layer of carefully 
proportioned dry cement and sand. This absorbent mix- 
ture withdraws some of the excess mixing water from 
the concrete. At the proper time the burlap is removed 
and the wearing course is floated and finished. This 
process has the effect of reducing the amount of mixing 
water in the wearing course, with the resulting advan- 
tages previously discussed. The work is done by well 
trained mechanics under careful supervision. 


5 


Resistance of Concrete to Industrial Products 


Impervious concrete is highly resistant to the action 
of many materials which would attack porous concrete. 
Lactic acid formed from milk products, weak acetic 
acid, brine solutions and some of the other materials 
used in industry will attack porous concrete, but will 
have very little effect on watertight concrete. Water- 
tight concrete requires impervious aggregates thoroughly 
incorporated in a cement-water paste which is itself 
impervious. 

Hard, dense aggregates meeting the requirements for 
wear resistance are impervious. Impervious paste is pro- 
duced by using alow amount of mixing water, not exceed- 
ing 31% to 5 gal. per sack of cement and keeping the 
concrete wet for a period. These conditions are necessary 
for the chemical process of hydration and are discussed 
under curing. 

The requirement for thorough incorporation of the 
aggregate makes necessary the use of sufficient cement- 
water paste to fill the voids in the aggregates and pro- 
vide a mix that will be thoroughly compacted when 
worked into place. 


The Importance of Curing 


The chemical reactions between cement and water 
which cause it to harden continue indefinitely if mois- 
ture is present and temperature is favorable. Through 
this curing process, the internal structure of the concrete 
is built up to provide strength, resistance to wear and 
watertightness. Floor finishes present such a large sur- 


6 


12 YEARS OF TRUCKING HEAVY LOADS—Trucks loaded with 4 tons or more of paper have been using this floor for 12 years at 
Woodward and Tiernan Printing Company, St. Louis, Mo. Careful control of water content, use of tough and well-graded aggregates 
and adequate curing are responsible for its good performance. 


face area that loss of moisture through evaporation 
takes place rapidly unless measures are taken to prevent 
such evaporation. Rapid drying not only stops the chem- 
ical reactions, but may cause dusting and also cracking 
of the surface due to shrinkage taking place at a time 
when the concrete has little strength. 

To prevent drying out, water for curing should be 
applied to the new concrete as soon as this can be done 
without marring the surface. It should then be kept 
wet or the moisture should be sealed in by covering the 
floor with waterproof paper or a membrane curing com- 
pound. The longer this curing period can be extended, 
the stronger, harder and more impervious will be the 
concrete. The curing period should be at least a week 
when using normal portland cement and 3 days when 
using high early strength portland cement. Special 
attention should be given areas near radiators or other 
sources of heat, to prevent evaporation during the cur- 
ing period. 


Some Things to Avoid 


Mortar mixes, that is, those containing sand and no 
coarse aggregate, should be avoided. 

Overly-wet mixes and mixes containing more than 
5 gal. of water per sack of cement should be avoided. 

Mixes which permit water or fine material to collect 
on the top surface should be avoided. 

Dusting on fine material to absorb excess water on 
the surface should be avoided for heavy-duty floors. 

Excessive troweling which brings water or a large 
amount of fine material to the surface should be avoided. 

Early drying should be avoided. 


CONSTRUCTION METHOUS FOR CONCRETE FLOOR FINISH 


LOOR finish may be placed after the base has hard- 

ened or while the base is plastic. The first method 
is preferred, as the finish is then put on after other 
building operations have been completed and therefore 
is less likely to be damaged. Better control of the water 
content is also obtained. Good results can be secured 
in either case if the base is properly prepared. 


It is essential that the base be of good quality to 
prevent the finish from pulling away from it. Floors 
on the ground should have base concrete made with 
not more than 6 to 6% gal. of water per sack of cement 
(about a 1:2144:31% mix). The quality in floors above 
ground is usually governed by structural requirements. 


Preparation of Hardened Base 


In new construction the base course should be brought 
to grade not less than 1 in. below the finish grade. When 
it has partially hardened so that it will retain the impres- 
sion of a broom, it should be brushed with a stiff-bristled 
broom, removing all laitance and scum. The brooming 
should expose some of the aggregate and score the sur- 
face to provide mechanical bond for the wearing course. 
The base should be wet-cured for at least 5 days unless 
high early strength portland cement or concrete is used 
which should be cured at least 2 days and it should be 
protected from grease, plaster, paint or other substances 
which would interfere with the bond. 


Immediately prior to placing the finished topping, the 
base course should be thoroughly cleaned by scrubbing 
with clean water and a stiff brush. Foreign substances 
not removed by the scrubbing should be chipped off. 
If the base has been allowed to dry out, it should be 
thoroughly wetted; preferably kept wet overnight. 
There should be no pools of water on the surface, how- 
ever, during the next operation. Thoroughly broom 
into the wet surface a slush coat of cement and water 
mixed to the consistency of thick paint, brushing out 
well to avoid too heavy a layer. The topping should 
then be placed immediately to avoid drying of the 
slush coat. 


Preparation of Base for Resurfacing 


On resurfacing jobs where the old floor level must 
be preserved, the old concrete must be cut away to a 
depth of 1 in. Where a new topping is to be placed 
directly over an old one without chipping off the old 
surface, the new topping should be at least 2 in. thick 
and reinforced with wire mesh, weighing not less than 
30 Ib. per 100 sq.ft. The surface of the old floor should 
be roughened with a pick or grinding tool. All loose 
particles, grease, oil, paint or other materials must be 
removed. Grease and oil may be removed by scrubbing 
with gasoline. Paint must be chipped off. Sandblasting 
is sometimes helpful, and scrubbing with a 10 per cent 
muriatic acid solution or with strong washing soda solu- 
tion is helpful in removing dirt and other substances. 

After the slab has been cleaned, it should be saturated 


overnight. A slush coat of cement and water should 
then be broomed into the surface just prior to placing 
the concrete for the topping. 


Base Preparation for Integral Finish 


When the finish is to be placed on the base before the 
latter has hardened, it is important to use a mix in the 
base which will not permit water to collect in puddles 
on the surface. If this occurs, the wearing course will 
absorb the excess water, greatly reducing the durability 
and strength of the finish. 

The mix for the base, therefore, should be adjusted 
if necessary to prevent water gain on the surface. Any 
water that collects on the surface of the base should 
be removed before the wearing course is applied. The 
base course should have stiffened sufficiently so that 
footprints will not be made by the workmen when they 
are placing the topping. 


Placing and Compacting the Topping 


The exact procedure to be followed in placing and 
compacting the topping will depend on whether or not 
a mechanical float is to be used. The concrete may be 
spread with shovels and ordinary garden rakes to a fairly 
uniform level, slightly above the finished grade, and com- 
pacted with tampers or rollers or both. It should then 
be struck off to grade, floated with mechanical or wood 
floats and finally troweled to the desired finish. 


ROUGHENING BASE TO INSURE BOND—Brushing the 
partially hardened base with a stiff wire broom cleans and 
scores the surface, thus assuring uniformity of bond. The 
surface of the hardened base must be clean, free from 
laitance and suitably roughened to secure good bond. 


POSED PHOTOGRAPH SHOWING STEPS IN FLOOR CONSTRUCTION—Note roughness of base slab and stiffness of concrete mix 
being spread with shovel and rake. Concrete is then tamped and screeded, followed by floating with mechanical floats. These operations 
are followed by troweling and curing. 


Tamping or Rolling 


Theconcrete should be compacted throughout itsdepth 
by tamping with iron tampers or rolling with weighted 
rollers. This gives a hard, compact topping which is 
essential for a durable floor. When rollers are used, par- 
ticular attention should be given the areas around col- 
umns and at walls where it is difficult to make rolling 
effective. Any areas that are not reached by the roller 
should be thoroughly tamped. 


Screeding 


Screeding is the operation of striking off the concrete 
to the proper level. When using the mechanical float 
some contractors place small precast concrete blocks in 
mortar at intervals of 8 to 10 ft. in both directions on 
the base. A surveyor’s level or straightedge and spirit 
levels may be used to place these at the proper level. 
After the concrete has been spread and tamped or rolled, 
a straightedge is placed over two of the blocks and 
moved with a sawing motion to compact the concrete. 
The straightedge is not moved horizontally. Thus a 
line of compacted concrete the width of the straightedge 
(usually about 1 in.) is provided between the two blocks 
and this forms the screed strip. The process is repeated 
between the next two blocks, and so on, giving screed 
marks every 8 or 10 ft. in two directions. Additional 
screed marks are made every 4 to 5 ft. in the same 
way, using the screeds already placed as guides. A scraper 
is then used to strike off the concrete to the level of 
the screed strips. The scraper should be about 5 ft. long, 
slightly beveled on the bottom and have a strip of steel 
on the face. The blocks are then removed and the spaces 
filled with concrete. 

When floating is done by hand, wood screed strips 
are often used. These are placed at the proper level 
with the aid of a surveyor’s level or spirit level. The 


8 


straightedge is moved across the strips in a sawing 
motion and at the same time is advanced horizontally 
to strike off the concrete. The strips are then removed 
and the spaces filled with concrete. 


Floating 


Floating is done to compact the surface, fill up the 
hollows and iron out the humps left after screeding and 
tamping or rolling. As previously stated, the power float 
machine will permit the use of a much stiffer, harsher 
mixture than can be used when floating with wood or 
cork floats by hand. The machine consists of a steel 
disk 20 to 24 in. in diameter on which a motor is mounted. 
By means of a handle the machine is operated over the 
surface of the floor. The rotating of the disk compacts 
the concrete and floats out the topping to a smooth sur- 
face. With the proper mixture only enough mortar will 
be brought to the surface for steel troweling. 


Troweling 


Troweling is an extremely important operation and 
one which requires experience and skill for the best 
results. It should be done at the proper time, which is 
after the concrete has hardened sufficiently to prevent 
drawing moisture and fine materials to the surface. When 
the mechanical float is used the first troweling may be 
done immediately after floating. When floating is done 
by hand it is necessary to use a more plastic mixture 
and therefore it is necessary to wait for a period after 
floating until the surface becomes fairly hard. Cement 
or mixtures of cement and sand should not be spread 
on the surface to absorb excess water nor should water 
be added to facilitate troweling. Final troweling should 
be done after the concrete is so hard that no mortar 
accumulates on the trowel and a ringing sound is pro- 
duced as the trowel is drawn over the surface. This will] 
polish the surface to a smooth finish. 


Curing 

Proper treatment of the floor after it has been trow- 
eled is too often neglected. As stated previously, the 
concrete must be kept moist so that the cement will 
continue to combine chemically with the water. This 
curing process should be started as soon as possible. 
If it is delayed so that rapid evaporation takes place in 
the early stages, the surface may crack, craze or dust. 
The longer the concrete can be kept wet, the stronger, 
more impervious and more wear-resistant it will be. 

There are several methods of curing concrete floors. 
The ponding method is sometimes used, in which the 
floor slab is surrounded by small dikes of sand and the 
enclosure kept filled with water to a depth of an inch 
or so. Frequent sprinkling of the surface and covering 
the exposed surface with wet sand or wet burlap are 
other ways of providing curing. Such coverings should 
be placed as soon as this can be done without marring 
the surface and then should be kept continuously wet. 

Heavy paper impregnated with asphalt to make it 
waterproof is also used for curing. This is placed as soon 
as it can be done without marring the surface and will 
protect the floor from dirt and debris resulting from 
other building operations. All seams should be lapped 
and sealed with glued tape to provide a continuous 
waterproof covering. Colorless membrane curing com- 
pounds are also used. 

In cold weather construction when artificial heating 
devices are used, special precautions are required. The 
high temperatures near the heating devices cause rapid 
drying unless the concrete is well protected. Heaters 
should be raised and the floor underneath for a distance 
of several feet on all sides of the heater should be covered 
with 3 or 4 in. of sand. The sand should be kept satu- 
rated with water through the curing period. 


Cold Weather Precautions 


Concrete hardens very slowly at temperatures below 
50 deg. F. and the hardening practically ceases at freez- 
ing temperature. Special precautions are required for all 
concrete work in cold weather, but because of the rela- 
tively thin layer of concrete and large area of exposure 
in floor finish, such precautions are particularly impor- 


tant. All concrete should be protected from freezing 
until it has gained sufficient strength so that it will not 
be damaged. When necessary, heat should be furnished. 

On leaving the mixer, the fresh concrete should be free 
from ice or frozen lumps and should have a temperature 
of not less than 60 nor more than 80 deg. F. Heating 
only the mixing water is often sufficient; in other cases 
it may be necessary to heat both mixing water and aggre- 
gate to meet these requirements. The concrete tempera- 
ture should then be maintained above 70 deg. F. for 
at least 3 days, or above 50 deg. F. for at least 5 days 
when using normal portland cement and above 70 deg. 
F. for at least 2 days or above 50 deg. F. for at least 
3 days when using high early strength portland cement. 
The floor should be kept wet during this period. 

Caution: The temperature of the hardened slab should be as near 
that of the new concrete as possible. Warm concrete placed on a very 
cold, hardened slab will not bond well and when the top course is 
cooled it may shrink enough to break away from the slab. 


Grinding 


Some concrete floors are finished by grinding. Mechan- 
ical grinders remove the thin film of cement paste that 
covers the surface after troweling, thereby exposing the 
aggregates. Such finish needs only one troweling. 

Grinding should not be started until the concrete has 
cured and hardened sufficiently so that aggregate par- 
ticles will be cut and not torn from the surface. Large 
double-disk electrically operated grinding machines, such 
as those used for finishing terrazzo floors, have been 
found economical. The floor is generally kept saturated 
during grinding. When necessary, air holes and pits may 
be filled with a cement grout of creamy consistency. 


Cleaning the Finish 


The new floor finish should be protected from accu- 
mulations of building debris until the completion of the 
structure. Toremove accumulated dirt, the surface should 
be well swept with a stiff broom and thoroughly scrubbed 
with white soapsuds. A scrubbing machine fitted with 
wire brushes or pads of fine steel wool is very effective. 
The suds and dirt should be mopped up and the surface 
flushed with clean warm water and again mopped. 


MECHANICAL FLOATING CONCRETE FLOOR FINISH—The ro- 

tating steel disc of the mechanical float compacts the concrete, 

smooths out the hollows and high spots and brings just enough 
mortar to the surface for troweling. 


CREEDING CONCRETE TO PROPER LEVEL—After tamping 

he concrete, screed strips are made at about 10-ft. intervals. The 

xcess concrete is then scraped off to the level of the screed strips, 
using a short screed fitted with a steel edge. 


PRODUCING AN EVEN CONCRETE FLOOR FINISH—A long 
float will remove the inequalities left by the short float and pro- 
duce an even, plane finish. Notice absence of water at surface. 


HAND FLOATING AND TROWELING CONCRETE FLOOR FINISH- 
Finishing operations play an important part in determining the utility 
appearance and durability of the wearing course. Proper floating fills u 
the hollows and compacts the concrete. It may be done by hand, as showr 
or by mechanical floats. Troweling further compacts the wearing cours 
and produces a smooth surface so necessary for efficient trucking. 


apecifications for Heavy-Duty Concrete Floor Finish 


1. Base Slab 


The surface of the structural base slab shall be finished reason- 
ably true and struck off at a level not less than 1 in. below the 
required finish grade. 

As soon as the condition of the concrete base permits and 
before it has fully hardened, all dirt, clay, oil, grease, plaster and 
loose aggregate shall be removed from the surface by means of a 
wire broom, which shall leave the coarse aggregate slightly ex- 
posed, or the surface otherwise roughened to improve bond with 
the topping. 

When it is impossible to remove laitance and roughen the slab 
by brooming, the surface shall be cleaned and prepared for bond 
by chipping after the base has hardened. 


Just prior to placing the finish, the base slab shall be thor- 
oughly cleaned by scrubbing, to the satisfaction of the engineer. 


Note: When the wearing course is to be placed on same day as 
the base slab, only the first paragraph of this section should be used. 


2. Portland Cement 


Portland Cement shall conform to Specifications for Portland 
Cement, ASTM Designation: C150; Specifications for Air-En- 
training Portland Cement, ASTM Designation: C175; Specifi- 
cations for Portland Blast-Furnace Slag Cement, ASTM Desig- 
nation: C205; or Specifications for Portland-Pozzolan Cement, 
ASTM Designation: C340; and shall be Type—. 

These specifications cover the types of portland cement listed 
below and provide that “‘when no type is specified, the require- 
ments of Type I shall govern.” 


“Type I, IA, IS, ISA, IP or IPA—For use in general 
concrete construction when the special properties of other 
types are not required. 

**Type Il or I1A—For use in general concrete construction 
exposed to moderate sulfate action, or where moderate heat 
of hydration is required. 

“Type If or IffA—For use when high early strength is 
required. 

**Type IV—For use when a low heat of hydration is required. 
‘Type V—For use when high sulfate resistance is required. 


‘‘Note—Attention is called to the fact that some of these 
types are not usually carried in stock. In advance of specify- 
ing their use, purchasers or their representatives should de- 


10 


termine which types of cement are or can be made available. 
“The letters ‘A,’ ‘S’ and ‘P’ after the type number designate 
air-entraining portland cement, portland blast-furnace slag 
cement and portland-pozzolan cement, respectively.” 
These paragraphs, including Note, are quoted from above 
specifications. 


3. Aggregates 


Fine aggregate shall consist of clean, hard sand or crushed 
stone screenings free from dust, clay, loam or vegetable matter 
and shall be graded from coarse to fine to meet the following 
requirements: 


Per Cent 
Passing 34-in. sieve . . i, 100 
Passing No. 4 sieve . eo oS KO) UY) 
Passing No. 8 sieve. . ..... . . .)BOlONOO 
Passing No. l6sieve ........... .50to 85 
Passing No. 30 sieve . . .-. . | . SanoHIGNEGG 
Passing No. 50 sieve... . . . . 9 squeegee 
Passing No. 100 sieve . yee tOmeLO 


Coarse aggregate shall consist of clean, hard gravel or crushed 
stone free from dust, clay, loam or vegetable matter, and from 
coatings which will tend to weaken the bond. It shall contain 
no soft, flat or elongated fragments and shall be graded to meet 
the following requirements: 


Per Cent 
Passing 34-in. sieve . ae 100 
Passing 14-in. sieve . . .90 to 100 
Passing 3-in. sieve . . .40to 70 
Passing No. 4 sieve . ey WO) 
Passing No. 8 sieve . «kee OStOmen 


All aggregates shall be selected with care and shall be of an 
approved character. Samples of proposed material shall be sub- 
mitted to the engineer for approval prior to use. 


4. Mixture 


The nominal mixture shall be 1 part of portland cement, 1 
part of fine aggregate and 2 parts of coarse aggregate by volume. 
This nominal mix may be slightly varied, depending upon the 
local conditions, and as the engineer may direct. If the aggregate 
is very coarse, the gravel or stone may be reduced, but in no 


case shall the volume of the coarse material be less than 1% 
times the volume of the fine. 


The mixture shall be determined by the engineer and once 
established shall not be changed except upon his written order. 

Not more than 4 gal. of mixing water, including the moisture 
in the aggregates, shall be used for each sack of portland cement 
in the mixture when floating is done by machine and not more 
than 5 gal. when floating is done by hand. 

The mixing of the concrete shall continue for at least 1 
minute after all ingredients are in the mixer. 


5. Consistency 


The concrete shall be of a consistency stiff enough to work with 
a sawing motion of the strike-off board, or straightedge. Any 
change in consistency shall be obtained by adjusting the propor- 
tions of fine and coarse aggregate within the limits specified- 
In no case shall the specified amount of mixing water be exceeded. 


6. Placing and Compacting 


The base slab shall be thoroughly wetted just prior to the 
placing of the finish, but there shall be no pools of water left 
standing on the wetted surface. A thin coat of neat cement grout 
shall be broomed into the surface of the slab for a short distance 
ahead of the topping. The wearing course shall be applied before 
the grout has hardened, and brought to the established grade 
with a straightedge. After striking off the wearing course to the 
established grade, it shall be compacted by rolling or tamping, and 
then floated with a wood float or power floating machine. The 
surface shall be tested with a straightedge to detect high and 
low spots, which shall be eliminated. 

Note: When the wearing course is to be placed on same day as 
the base slab, the following should be substituted for the first three 
sentences of this section: 

Water and laitance which rise to the surface of the base slab 
shall be removed before applying the wearing course. After con- 
crete in the base slab has settled sufficiently so that water does not 
rise to the surface but within 2 hours after placing the base slab, 
the wearing course shall be applied and brought to the established 
grade with a straightedge. 


7. Finishing by Troweling 

Floating shall be followed by steel troweling after the concrete 
has hardened sufficiently to prevent excess fine material from 
working to the surface. The finish shall be brought to a smooth 
surface free from defects and blemishes. No dry cement nor mix- 
ture of dry cement and sand shall be sprinkled directly on the 
surface of the wearing course to absorb moisture or to stiffen the 
mix. After the concrete has further hardened, additional troweling 
may be required. This shall be done as may be directed by the 
engineer. 


Specilications 


Many old floors have been subjected to service that was too 
severe for the quality of the surface. Such floors may be resur- 
faced to provide a topping which will withstand heavy duty 
indefinitely. The specifications for heavy-duty floors may be used 
by changing designated paragraphs as follows: 


Where old floor level must be preserved and where it is otherwise 
practicable to chip off the old floor topping, substitute the following 
for Section 1: 


1. Base 


The top of the old floor shall be removed to a depth of at least 
1 in. The base shall be thoroughly cleaned of all loose material 
and dust to the satisfaction of the engineer. 


Where it is not practicable to chip off the old topping and the 
floor level may be raised, the following provisions may be substituted 
for Sections 1 and 6: 


Note: Surfaces to be ground shall be swept with soft brooms after 
rolling to remove any water and surplus cement paste that may be 
brought to the surface. The wearing course shall then be floated and 
once lightly troweled, but no attempt shall be made to remore all 
trowel marks. 


8. Curing and Protection 


All freshly placed concrete shall be protected from the elements 
and from all defacement due to building operations. The con- 
tractor shall provide and use tarpaulins when necessary to cover 
completely or enclose all freshly finished concrete. 

If at any time during the progress of work the temperature 
is, or in the opinion of the engineer will, within 24 hours, drop 
to 40 deg. F., the water and aggregate shall be heated so that the 
concrete temperature is between 60 and 80 deg. F. at the time of 
placing and precautions shall be taken to maintain the tempera- 
ture of the concrete above 70 deg. F. for at least 3 days or above 
50 deg. F. for at least 5 days when using normal portland cement, 
and above 70 deg. F. for at least 2 days or above 50 deg F. for 
at least 3 days when using high early strength portland cement. 

As soon as the concrete has hardened sufficiently to prevent 
damage thereby, it shall be covered with at least 1 in. of wet 
sand or other covering satisfactory to the engineer, and shall be 
kept continually wet by sprinkling with water for at least 7 days 
when using normal portland cement or for at least 3 days when 
using high early strength portland cement. In lieu of other curing 
methods, the concrete may be covered with a colorless curing 
compound or with asphalt-impregnated, waterproofed paper. All 
seams of such paper shall be overlapped and sealed with tape. 

Note: When the surface is to be finished by grinding add the 
following section. 


9. Finishing by Grinding 

After the wearing course has hardened sufficiently to prevent 
dislodgment of aggregate particles, it shall be ground down with 
an approved type of grinding machine shod with rapid-cutting 
abrasive stones to expose the coarse aggregate. The floor shall 
be kept wet during the grinding process. All material ground off 
shall be removed by squeegeeing and flushing with water. 

Air holes. pits and other blemishes shall then be filled with 
a cement grout of creamy consistency. This grout shall be spread 
over the surface and worked into the pits with a steel straightedge, 
after which the grout shall be rubbed into the floor surface with 
the grinding machine. The floor shall be kept moist for an addi- 
tional 3 days but for not less than the time required in Section 8. 

The surface shall then receive a second or final grinding to 
remove the film and to give the finish a polish. It shall then 
be thoroughly washed and all surplus material removed. 


for Resurfacing 


1. Base 


The top of the old floor shall be thoroughly cleaned of all 
loose material, dust, paint, grease, oil or other material to the 
satisfaction of the engineer. Areas having the original troweled 
finish shall be roughened. 


6. Placing and Compacting 


The base slab shall be thoroughly wetted prior to placing the 
finish, but there shall be no pools of water remaining when the 
wearing course is to be placed. A thin coat of neat cement grout 
shall be broomed into the surface of the slab for a short distance 
ahead of the topping. Before the grout hardens, the wearing course 
shall be applied to a thickness of about 1 in. Wire mesh weighing 
not less than 30 lb. per 100 sq.ft. shall be laid and placing of the 
wearing course resumed to a total thickness of not less than 2 in. 
After striking off the wearing course, it shall be compacted by 
rolling or tamping and then floated with a wood float or power 
floating machine. The surface shall be tested with a straightedge 
to detect high and low spots, which shall be eliminated. 


1] 


Job experience and tests have proved that wearing 

quality of a concrete floor is largely controlled by the 
proportions of cement, sand and coarse aggregate and the 
amount of mixing water. A concrete floor finish made with 
a large percentage of sand as compared with the quantity 
of coarse aggregate may work easily under the trowel (see 
Illustration 6) but it will not be durable. A good mix is 1 
part portland cement, 1 part sand and approximately 2 
parts coarse aggregate. Not more than 4 gal. of water per 
sack of cement for machine floating and 5 gal. for hand 
floating should be used in the mixture, including the free 
water in the aggregates, which should be carefully deter- 
mined and deducted from the specified quantity. 


4 The manipulation of the wearing course has much 
to do with its durability. The once common practice of 
striking off a wet mixture of mortar and then troweling 
it while still plastic until there was a layer of fine material 
at the surface was largely responsible for crazing, dusting 
and poor wear-resistance. Proper procedure is to strike off 
topping to grade with a straight-edge, then compact it 
with tampers or rollers and float with a wood or power 
float to fill hollows and smooth out any humps left by 
screeding. After this has been done, do not steel trowel 
until absolutely necessary, under average conditions 30 
to 45 minutes. When a power float is used, it is usually 
possible to trowel immediately after floating. The surface 
is not touched with a steel trowel until all water has 
disappeared, in fact until no water sheen is visible. 


12 


A Pictorial Study of Correct Proce 


Good bond between the base slab and the wearing course 

is essential. It is readily accomplished by attention 
to the preparation of the base. It is recommended that 
the wearing course for heavy-duty floors be placed after 
the base has hardened, as better control of quality is pos- 
sible. To insure good bond, roughen the base before it has 
hardened to expose the aggregates slightly. All laitance, 
dirt or loose aggregate should be removed by means of 
wire brooms or stiff-bristle brooms. Just before placing 
the wearing course, scrub the base thoroughly and keep 
it uniformly wet but do not leave pools of water. Next 
broom a neat cement grout into the base and place and 
tamp the wearing course before the grout hardens. 


It will require considerable effort to trowel the sur- 
face after it has been undisturbed for 30 to 45 minutes, 
because of the stiffening of the concrete. Close supervision 
will be necessary to be sure the finishers do not start trowel- 
ing too soon. The drying of the surface moisture before 


troweling must proceed naturally and must not be has- 
tened by dusting on dry sand or cement. By delaying 
troweling as recommended, the concrete will have hard- 
ened sufficiently so that all the materials will remain 
where deposited. Objectionable fine material and water 
will not be brought to the top and the coarse particles 
will remain at the surface. An impervious wear-resistant 
floor free from maintenance cost and trouble will result. 


Concrete Floor Finish Construction 


The difference between a properly constructed concrete 

floor and one improperly made is quickly apparent by 
cutting a section through the floor. A correctly propor- 
tioned wearing course, placed in the manner herein recom- 
mended, will show uniform distribution of coarse aggre- 
gate particles through the entire depth of finish and right 
up to the wearing surface. There is no film of laitance or 
weak mortar at the surface. When thoroughly cured to 
develop the strength of the cement-paste binder, concrete 
is impervious and strong. There will be no dusting or craz- 
ing. A floor finish of this type will meet every traffic demand 
placed upon it. Such construction insures years of satis- 
factory service. 


Cement and sand mortar should never be used for 

heavy-duty floors and for that matter should be avoid- 
ed even for light traffic. There are no large particles of dur- 
able aggregate in a topping of that kind to resist wear. 
Because it is made of fine material only, the mortar works 
easily and a very smooth finish can be produced. For this 
reason it has been all too commonly used without thought 
as to its wear-resistant qualities. The economy and dur- 
ability of correctly constructed concrete floors is lost if 
weak mortar is used. Although the cost of placing a mortar 
finish may be slightly less than that for a 1:1:2 concrete 
wearing course, maintenance charges will soon offset any 
apparent saving. 


Crazing of the surface of a concrete floor is evidence of 

excessive shrinkage occurring before strength has been 
developed. It frequently results when mortar is used for 
the wearing surface. The large percentage of sand and 
the absence of coarse aggregate in such a finish necessitate 
a high water-cement ratio, which is one of the funda- 
mental causes of shrinkage. To avoid a high water-cement 
ratio in mortar, a mixture rich in cement must be used, 
but this also results in excessive shrinkage. The solution 
is in the use of the recommended mixture of 1 part ce- 
ment, | part sand and 2 parts coarse aggregate mixed with 
not more than 4 gal. of water per sack of cement for ma- 
chine floating and 5 gal. for floating by hand. Over-trowel- 
ing the finish while still plastic, dusting on sand or cement 
and inadequate curing also induce crazing. 


The reason for the unsatisfactory results from a mortar 

wearing course or one that has had a dust coat of fine 
material spread over the surface is clearly evident when 
a section is cut through the floor. A layer of weak material 
is revealed at the surface of the floor. Over-troweling has 
caused the finest particles in the finish and water to rise 
to the top. This surface skin has little strength. It shrinks 
badly, causing crazing, followed by dusting and disinte- 
gration under traffic. Comparison of a section through an 
improperly constructed concrete floor finish and one that 
has been made as herein recommended (Illustration 5) 
clearly shows why the former is weak and unsatisfactory 
while the recommended type is durable and wear-resistant. 


13 


‘enact 


osagiaisin Sete ee 


Architect, Fellheimer and Wagner, New York City. 


ROTUNDA OF THE CINCINNATI UNION TERMINAL—Color and bold pattern in this beautiful terrazzo floor com- 


plement the mosaic murals on the walls and the colorful dome to produce a harmonious and magnificent interior. 


DECORATIVE CONCRETE FLOOR FINISHES 


Terrazzo 


ERRAZZO floor finishes offer unlimited possibilities 

for decorative effects in concrete, thus combining 
beauty and durability. In large areas of plain color or 
in patterns of many colors, terrazzo floors are widely 
used in banks, office and hotel buildings, churches and 
other public or social buildings, display and sales rooms, 
vestibules, lobbies and corridors, and are finding popular 
acceptance in the home. 


Plain terrazzo provides attractive, long-wearing floors 
at low cost. More decorative effects are produced by 


14 


introduction of pattern and by increasing the number 
of colors. The original beauty of terrazzo is retained with 
a minimum of upkeep and terrazzo surfaces are easily 
kept clean and sanitary. Stairs, ramps, coves, bases and 
wainscots are also made in terrazzo to match or contrast 
with the floors. 

Terrazzo is produced by laying mixtures of concrete 
containing marble chips or other aggregates of the desired 
colors. Additional aggregate is rolled into the fresh con- 
crete when necessary so that 70 to 85 per cent of the 
finished floor area will consist of aggregate. Coloring pig- 


FEW UF THE COLOR COMBINATIONS USED IN FINE TERRAZZO 


a? 


Belgian Black marble. Domestic White marble. Red Levanto marble and green and 
black pigments. 


be 


Coral Pink marble. 


Yellow Verona marble. 


PF o? a ae 3 
F ‘ ; ° 
2 q \e 
o 
canis er 
i \ 
E 
% 
ay o 
Ne ad 
bra RR Sco SB : P # a ae i Pia uf ei Meee Se) 


Red Rosa marble. 


Red Verona marble. 


Yellow Verona marble and yellow 


pigment, 
x 
e 2 i 
a lk 
¥ 
i 


Pe 


a a ates. 


Red toes Paarhle Pend wedi mimo 


Red Champlain marble and red and 
black pigments. 


15 


ments may be added to produce a matrix of almost 
any shade and color desired. White portland cement 
should be used where clarity of color is important. After 
the concrete mixtures have hardened for several days, 
the surface is ground and highly polished. 

Brass strips or dividing strips of other suitable mate- 
rial are used to separate the colors for the desired pat- 
tern. They also prevent shrinkage cracks which are 
particularly objectionable in decorative floors. The ter- 
razzo course may be bonded to the structural base slab 
or may be separated by means of a sand cushion 14 in. 
thick and a layer of tarpaper. Structural cracks which 
occur in the base slab will not be transmitted to the 


Specilications for 


1. Base Slab 


The surface of the structural base slab shall be struck off rea- 
sonably true at a level not less than — in. below the required 
finish grade. 

Note: Insert 134 in. for Method A or 2% in. for Method B. 


2. Samples 


Samples of the aggregates shall be submitted for approval by 
the architect. Samples of the terrazzo shall be made in duplicate 
for approval by the architect. 


3. Aggregates 


The aggregates shall be (insert the kind and color desired) 
and graded in sizes No. 1, 2 and 3. 


4. Color Pigments 


Pigments shall be commercially pure natural or synthetic min- 
eral oxides or other coloring materials manufactured for use in 
portland cement mixtures and proved satisfactory. Pigments shall 
be in the manufacturer’s original container. 


5. Mixtures 


The base for terrazzo finish shall be mixed in the proportions 
of 1 part of portland cement to 4 parts of clean, coarse sand. 

The terrazzo mixture shall be in the proportions of 200 lb. of 
aggregate to 1 sack of portland cement (where clear colors are 
important, use white portland cement) with not more than 4 gal. 
of water and the proper amount of pigment to produce the approved 
color. The cement and pigment shall be mixed dry to a uniform 
color before adding the other materials. The terrazzo mixture 
shall be of the driest consistency possible to work into place with 
a sawing motion of the strike-off board or straightedge. Changes 
in consistency shall be obtained by changes in the proportions 
of aggregate and cement. In no case shall the specified amount 
of mixing water be exceeded. 


6. Placing 


Method A—Bonded Finish—The surface of the structural base 
slab shall be cleaned of all plaster and other materials that would 
interfere with the bond and shall be thoroughly wetted. It shall 
be slushed with a neat cement grout thoroughly broomed into 
the surface. The underbed shall then be spread uniformly and 
brought to a level not less than 4 in. nor more than 34 in. below 
the finished floor. 

Method B—Broken Bond Finish—The surface of the struc- 
tural base slab shall be covered with a uniform layer of fine sand 
JY in. thick, and covered with an approved tarpaper overlapping 
at least 2 in. at all edges. The underbed shall then be spread 
uniformly and brought to a level not less than 14 in. nor more 
than 34 in. below the finished floor. 

While the underbed is in a semi-plastic state, the dividing strips 
shall be installed to conform to the designs shown on the draw- 


*A dditional information on terrazzo floor construction and main- 
tenance can be obtained from National Terrazzo and Mosaic Asso- 
ciation, Washington, D.C. 


16 


terrazzo top course if this is separated from the base. 

An underbed of 1:4 mortar, about 11% in. thick, is 
placed and the dividing strips are inserted in the mortar 
in the desired pattern. When this has hardened suffi- 
ciently, the terrazzo mixtures consisting of 1 part of 
portland cement and 2 parts of aggregate are applied. 
The floor is then rolled until thoroughly compacted and 
after hardening sufficiently it is ground and polished. 

Skilled labor working under adequate supervision is 
necessary for a good terrazzo job. The work should be 
entrusted to floor specialists whose experience has shown 
them capable of rendering the class of workmanship 
desired. Specifications for terrazzo floor finishes follow.* 


Terrazzo Work 


ings. The top of the strips shall be at least 4% in. above the finished 
level of the floor. 

The terrazzo mix shall then be placed in the spaces formed 
by the dividing strips and rolled into a compact mass by means 
of heavy rollers, adding aggregate if necessary so that the finished 
surface shall show a minimum of 70 per cent aggregate. [mme- 
diately after rolling, the surface shall be floated and troweled 
to an even surface disclosing the lines of the strips on a level with 
the terrazzo filling. 


7. Curing and Protection 


All freshly placed concrete shall be protected from the elements 
and from all defacements due to building operations. As soon 
as the concrete has hardened sufficiently to prevent damage 
thereby, it shall be covered with at least 1 in. of wet sand or 
other covering satisfactory to the architect, and shall be kept 
continually wet by sprinkling with water for at least 7 days when 
using normal portland cement and for at least 3 days when using 
high early strength portland cement. The temperature of the 
concrete at time of placing shall be between 60 and 80 deg. F. and 
it shall be maintained above 70 deg. F. for at least 3 days or above 
50 deg. F. for at least 5 days when using normal portland cement 
and above 70 deg. F. for at least 2 days or above 50 deg. F. for 
at least 3 days when using high early strength portland cement. 


8. Surfacing 


When the terrazzo concrete has hardened enough to prevent 
dislodgment of aggregate particles, it shall be machine rubbed, 
using No. 24 grit abrasive stones for the initial rubbing and No. 
80 grit abrasive stones for the second rubbing. The floor shall 
be kept wet during the rubbing process. All material ground off 
shall be removed by squeegeeing and flushing with water. 

A grout of portland cement, pigment and water of the same 
kind and color as the matrix shall be applied to the surface, filling 
all voids. 

In not less than 72 hours after grouting, the grouting coat 
shall be removed and the surface polished to a satisfactory finish 
by machines using stones not coarser than No. 80 grit. 


9. Cleaning 


After removing all loose material, the finish shall be scrubbed 
with warm water and soft soap and then mopped dry. 


10. Non-Slip Terrazzo 


Where specified, the terrazzo shall be made non-slip by the 
addition of abrasive aggregate meeting the approval of the archi- 
tect. The abrasive shall be mixed with the terrazzo mixture or 
sprinkled on the surface only as indicated. Where it is to be mixed 
with the terrazzo mixture, the aggregate shall consist of 40 per 
cent abrasive aggregate and 60 per cent of other aggregate as 
specified. Where it is to be sprinkled on the surface only, the 
finished surface shall show uniform distribution of 1 part of abra- 
sive aggregate to 4 parts of other aggregate as specified. 

Note: It is suggested that for heavy-duty floors the abrasive be 
incorporated in the terrazzo mizture. For light-duty floors it may 
be sprinkled on the surface. 


Concrete Tile and Art Marble 


Beautifully colored, long-wearing floors of precast con- 
crete tile are used in residences, office buildings, hotels, 
churches and similar structures. When made of marble 
chips and ground and polished, the tile are often referred 
to as art marble. The tile may be secured in many colors, 
shapes and patterns, and special designs may be made 
to order. They should be secured from reliable manu- 
facturers. 

When tile are to be installed, the concrete base course 
is brought to within 2 or 214 in. of the finished grade, 
left with a rough surface and allowed to harden. Mortar 
of 1:3 mix is placed on the dampened base and the tile 
are laid in the desired pattern. Before the tile are laid, 
they should be soaked in water for 10 or 20 minutes, 
and then allowed to dry for about the same length of 
time, the object being to have them uniformly damp, 
but not saturated with water. Tile should be laid by 
experienced mechanics. 


Color with Pigments 


A wide range of color is obtainable with the use of 
mineral coloring pigments mixed with the concrete fin- 
ish. A single uniform color such as red, green or brown 
is most widely used in floors of this type, although a 
border of one color and field of another as well as simple 
patterns involving two or more colors have been used 
to some extent. 

Only pigments resistant to alkali should be used. Mor- 
tar colors containing a large percentage of filler are not 
suitable. Pure mineral pigments conforming with the 
specifications of the American Society for Testing 
Materials or the Federal Government specifications listed 
in the accompanying table should be used. Concrete con- 
taining pigment should be mixed thoroughly to secure 
uniform dispersion and full color value of the pigment. 

Various methods of mixing are used. The pigment may 


PIGMENTS FOR COLORED CONCRETE FLOOR FINISH 


— 
Shades of peer Specifications 
esignation 
oer é ASTM | Federal 
Grays to Black oxide of iron or D-769 | TT-I-698 
black carbon black* D-561 
Blue Ultramarine blue D-262 | TT-U-450 
Bright red Red oxide of iron D-84 TT-I-5lla 
to deep red 
Brown Brown oxide of iron TT-I-702 
Ivory, cream | Yellow oxide of iron D-768 | TT-Y-216 
or buff 
Green Chrome oxide or green-| D-263 | TT-C-306 
ish blue ultramarine D-262 | TT-U-450 


*Carbon black is very light in weight and usually 14 to 1 lb. per 
sack of cement is sufficient. Thorough mixing is required to dis- 
perse the pigment. 


be added to the other dry ingredients and mixed thor- 
oughly before the water is added. A color mixer or small 
ball mill may be used to mix the cement and pigment 
to a uniform color before these are added to the aggre- 
gate and water. Another method of mixing the pigment 
and cement is to pass them through a 1%-in. or finer 
sieve until the mixture is uniform. After all the ingre- 
dients are in the mixer, the batch should be mixed for 
at least 2 or 3 minutes and until it is uniform. 

The color values of pigments vary with their fineness 
and purity. In comparing them, one should be guided 
by the amounts required to produce the desired color 
and shade. This can best be done by making test samples, 
allowing them to dry. Generally from 5 to 9 lb. of pigment 
per sack of cement is required depending on the shade 
desired. Usually 1% to 1 Ib. of carbon black is sufficient. 


Dusted-on Color 


For some floors subject only to light foot traffic, a 
dusted-on color mixture has been used. A 1-in. wearing 
course as recommended for heavy-duty floors is placed, 
and after screeding to the proper level a dusted-on mix- 
ture is applied immediately. This mixture is made in 
the proportions of about 1 part of cement, 1 to 14% 
parts of sand and the required amount of pigment. The 
sand should be well graded with at least 80 per cent 
passing a No. 8 sieve and not more than 3 per cent pass- 
ing a No. 30 sieve. The mixture should be applied uni- 
formly at the rate of not less than 125 lb. per 100 sq.ft. 
of floor area. 

After spreading the dry material it should be floated 
and worked into the slab. The first floating should be 
discontinued as soon as the surface becomeswet. Floating 
should be resumed when surface moisture has disap- 
peared. After testing with a straightedge and high and 
low spots are eliminated, the finish should be troweled 
to a smooth surface free from defects or blemishes. The 
concrete should then be cured as recommended for other 
floor finishes. 


Stained Floor Finish 


Attractively colored floors are secured with the use 
of certain inorganic chemicals. These are applied to the 
hardened floor and react with the cement to form new 
compounds in the concrete to produce the color. Several 
applications are often necessary before the desired effects 
are attained. A mottled or multi-tone effect is generally 
produced, depending somewhat on the amount of trow- 
eling done in finishing. A number of manufacturers can 
supply the materials used. 


Painted Finish 


Concrete floor finish may be painted to attain any 
color effect. Oil paints, rubber-base paints and synthetic 
resin paints are available for this purpose. It should 
be realized that any traffic causes a certain amount of 
wear and in aisles and other places where foot traffic 


iy 


METAL DIVIDING STRIPS IN PLAIN CONCRETE FLOOR—Metal dividing strips like those used in terrazzo are often used 
in plain or colored concrete floor finish. This floor is in locker room of gymnasium at Amherst College, Amherst, Mass. 


is heavy, touching up at intervals may be necessary 
and an occasional complete repainting required to keep 
a good appearance. Painting is not advisable where 
there is heavy truck traffic or dragging of boxes or other 
objects over the floor. 

Concrete should be clean and thoroughly dry when it 
is to be painted. The recommended procedure in the 
past has been to allow several months after construction 
for curing and drying and then to neutralize the surface 
by mopping it with a solution containing 2 to 3 lb. of 
zinc sulphate per gallon of water. After allowing 48 
hours for this solution to react with the concrete and to 
dry, the surface is cleaned with water to remove all 
crystals. It is then allowed to dry thoroughly before 
applying the paint. 

Recent laboratory tests indicate that an even better 
procedure is to allow the concrete to dry for several 
weeks after the curing period; then apply generously a 
solution of 3 oz. zinc chloride and 5 oz. of ortho-phos- 
phoric acid (85 per cent phosphoric acid) per gal. of 
water. After drying 24 to 48 hours, any dust on the sur- 
face should be brushed off but the surface should not be 
rewetted before applying the paint. While the labora- 
tory tests gave excellent results with this treatment 
actual field applications have been very limited up to 
the present time. 

Three coats of paint are recommended. The first coat 
should be very thin—about equal parts of thinner and 
paint give about the proper consistency. Some thinner 
may be used for the second coat and the third coat 
may be applied as it comes from the can. 


18 


scoring and Division Strips 


Concrete floors may be marked off into conventional 
patterns by the use of an ordinary grooving tool on the 
fresh concrete or with a power-driven carborundum disk 
cutting appliance on the hardened concrete. An objec- 
tion to grooves is the difficulty of keeping them clean. 
When the floor is mopped the dirt is deposited in the 
grooves. 

Another method of marking off the floor surface is 
with metal strips like those used for terrazzo. These 
have the advantage of eliminating open scoring joints. 
Shrinkage of the surface tends to localize along the 
strips, thus preventing surface cracking. The strips are 
available in brass, nickel silver and zinc in 12 to 18 
gage and from | to 13% in. wide. For joints more than 
Y in. wide, strips of the “heavy top” type are used. 

Division strips are used both in single color floors 
and in floors having two or more colors. In general, 
they should be placed not more than 4 ft. apart to be 
effective. In floors to be finished by troweling and not 
to be ground, care must be exercised to set the strips 
at the exact finished level. 


Dance Floors 


Smooth concrete floors make excellent surfaces for 
dancing. Terrazzo and trowel finished colored floors are 
widely used for interior dance floors. Concrete is also 
ideal for out-of-doors dance floors as it resists weather- 
ing, is quickly put into service after rain and requires 


a minimum of maintenance. Many hotels, summer gar- 
dens, country clubs and similar organizations have built 
such outdoor floors. 

Outdoor floors should be designed and constructed 
to withstand the wide range of temperature variations 
and conditions of weathering. When placed directly on 
the ground, drainage away from the floor should be pro- 
vided. A well drained cinder, gravel or crushed stone 
fill at least 6 in. thick should be provided. A base slab 
at least 4 in. thick of 1:2:3 concrete should be placed 
on the fill. While still plastic, temperature reinforcement 
should be placed on this concrete, followed immediately 
by the finish course. The finish should be constructed 
as recommended for heavy-duty floors. 

Temperature reinforcement should consist of at least 
Yj-in. bars, spaced at 6-in. centers in both directions, 
or an equivalent area of steel in wire fabric or expanded 
metal. In unstable earth, structural reinforcement may 
be needed in the lower part of the slab. A competent en- 


gineer should be consulted for such cases as well as for 
floors of exceptional area and irregular shapes. 

Dance floors must be smooth and preferably waxed. 
When such floors are given a trowel finish, a very hard, 
smooth surface is secured by troweling after the con- 
crete is hard enough to produce a ring as the trowel 
passes over it. Terrazzo floors are polished by mechan- 
ical equipment and are very smooth. 

Various treatments are used for preparing concrete 
floors for dancing. In most cases a satisfactory polish 
is secured with ordinary floor wax. Paste wax should 
be used for the first two or three applications; after that 
either paste or liquid wax may be used. Powdered wax, 
powdered boric acid and powdered soap also are suit- 
able. Some floors have been treated with paraffin wax 
dissolved in turpentine, followed by a coating of pow- 
dered wax. 

Scrubbing the floor with strong soap solution before 
waxing and an occasional scrubbing and rewaxing are 
desirable to keep the floor in good condition. 


FLOORS SUBJECT TO SPECIAL CONDITIONS 


Creameries, pickling and packing plants, food products plants, breweries—Floors 


exposed to impact, rapid changes in temperature, strong acids or corrosive materials 


OME materials used in industry will attack concrete 
of inferior quality but will have little if any effect 
on impervious concrete floor finish. Lactic acid as found 
in some milk products and vinegar or other organic 
acids resulting from fermentation of food products, fruit 
juices and many other materials are in this class. The 
smoothness of properly constructed concrete floors, their 
low absorption and their freedom from joints and crey- 
ices prevent the accumulation of these materials and 
make it relatively easy to keep them clean. 

Other materials such as salt or sugar solutions will 
be absorbed by porous floors. Due to crystallization of 
the absorbed solution, sufficient stress is created to cause 
gradual disintegration. Concrete floors of good quality 
will not absorb the solution and hence will withstand 
the action of these materials indefinitely. 

For all these exposures, then, concrete floor finish con- 
structed as recommended for heavy-duty floors should 
be provided. As further protection against the possibil- 
ity of absorbing any of these materials, a surface treat- 
ment may be used to fill the surface pores. The treatment 
is given after the concrete has cured and dried. 

A simple treatment is the application of warm linseed 
oil, Chinawood oil or soybean oil. To assist penetration, 
the oil should be thin. For the first coat, equal parts 
of the oil and turpentine or other suitable thinner may 
be used. A second application with a somewhat thicker 
solution may be given if the first one is well absorbed. 
The oil may be applied with mops or brushes and the 
excess removed with a squeegee before the oil gets tacky. 


An occasional application of the oil after the floor is 
in service will be helpful. This should be done only 
after the floor has been thoroughly cleaned. 

Another treatment is the application of paraffin. The 
paraffin should have a melting point of 150 deg. F. It 
is made into a paste by melting 4 parts by weight with 
1 part of turpentine and 16 parts of toluol. Toluol is 
a solvent obtained from coal tar and is generally avail- 
able from chemical supply houses. The mixture is spread 
on the floor and allowed to penetrate for 24 hours. The 
floor should be as warm as possible. At the end of this 
time the residual layer should be driven into the con- 
crete by heat. A free flame should not be used due to 
fire hazard; hot irons will be found safe and effective 
in forcing the paraffin into the pores of the finish. 

After either of these treatments, the floor may be 
waxed for further protection. As the wax film is worn 
away, it should be replaced. A floor-polishing machine 
may be used. Waxing is of considerable assistance in 
keeping the floor clean. 


Rapid Temperature Changes 


In many creameries and other plants, large vats of 
boiling water are dumped onto the floor to flow into 
drains, subjecting the concrete to rather rapid changes 
in temperatures. Light wire mesh may be placed in the 
finish course to reinforce the concrete and prevent cracks 
due to this type of service. The mesh should be 4x4-in. 
No. 10 gage wire weighing 31 lb. per 100 sq.ft., and 
should be placed near the middle of the wearing course. 


19 


Armored Floors 


Concrete floor finish in receiving rooms, unloading 
platforms and in other locations where they will be sub- 
ject to impact from falling objects may be reinforced 
with a special metal grid or armor grating placed in 
the surface. Armoring is also used in floors to be sub- 
jected to heavily loaded steel-tired trucks or to sliding 
loads. Armor of several varieties is available consisting 
of grey iron castings, strips of steel assembled by bolts, 
welding, rivets or wires, and cold-drawn carbon steel 
open-work sections 

The armor should be installed in accordance with the 
manufacturer’s recommendations with the top surface 
at the exact level of the finished floor. Care should be 
taken to fill all openings in the grille. The concrete should 
be made, placed, finished and cured as recommended 
for heavy-duty floors. 


Acid-Proof Floors 


Floorsin chemical laboratories, acid plants, dye houses, 
storage battery buildings and similar structures in which 
strong acid solutions or other strong corrosive materials 
are manufactured or handled may require the protection 
of an acid-proof covering. Asphalt mastics, asphalt blocks 
or acid-proof brick or tile laid in acid-proof mortar may 
be used for this purpose. | 

The base slab is placed and finished some distance 
below the grade of the finished floor surface, depending 
on the thickness of the finish. The surface may be screeded 
to proper elevation, pitching it to the drainage fixtures 
whichalso should be ofacid-proof material. Where asphalt 
block are to be used, the surface should be troweled 
smooth. The base should be kept moist and allowed 
to harden before the top course is laid. 

Asphalt block may be placed directly on the base, 
setting them as close together as possible. The surface 
is then pointed with hot asphalt and a layer of clean 
fine sand is dusted on. The block weld to a continuous 
surface under traffic. Mixtures of asphalt and aggregate 
may be installed also as a continuous sheet from 1 to 
1% in. thick. Asphalts should not be exposed to hot 
water or other hot materials, fats, greases or oils. 


When brick or tile are used, these may be set in an 
underbed of cement mortar, leaving the joints open. 
The joints may then be filled with acid-proof material. 

For certain corrosive conditions, notably dilute solu- 
tions of sulphuric acid and sulphates, a concrete floor 
topping using a calcium aluminate cement with acid 
resistant aggregates has proven satisfactory. Calcium 
aluminate cement differs from portland cement in its 
composition. It is used in much the same manner, but 
requires all of its curing within 24 hours after mixing 
because of its rapid hardening. 


Non-Slip Floors 


In certain locations, more non-slip quality than usual 


20 


A METHOD OF PRODUCING A COARSE-GRAINED 

FINISH—After the surface has been troweled, the surface 

is lightly brushed in one direction with a hair broom to 

produce small grooves. For areas subject to heavy duty, 

coarse-grained finish is obtained better by the use of non- 
slip aggregates embedded in the surface. 


is desired in floor finish. This may be accomplished by 
roughening the surface immediately after final troweling 
or by incorporation of non-slip aggregates. Roughening 
may be done with a fine hair brush but this finish is 
seldom used for interior floors because of the difficulty 
in keeping the floor clean. 

Non-slip aggregates may be mixed with the concrete 
or sprinkled on the surface of the wearing course just 
prior to finishing. More of the aggregate is required 
when it is mixed with the concrete but the distribution 
is more uniform. Approximately 34 to 1 lb. of non-slip 
aggregate is required per square foot of floor. 

When applied only to the surface, from 14 to 1% lb. 
of abrasive is used per square foot. The aggregate should 
be scattered uniformly over the unhardened concrete 
just prior to compacting and worked into the surface 
during finishing. After the floor has hardened, the sur- 
face may be ground or scrubbed with floor-scrubbing 
machines using pads of steel wool. This removes the 
film of cement on the surface and exposes the non- 
slip aggregate. 


COVERED FLOORS 


HERE concrete floors are to be covered with 

linoleum, composition tile, prefinished wood tile 

or planking, carpeting or similar materials, it is not 

necessary to provide a heavy-duty wearing surface on 

the concrete. The dust coat method of finishing may 
then be used. 

The structural slab is struck off reasonably true at 
the required floor level and excess water or laitance 
removed. A mixture of dry materials consisting of 1 part 
of portland cement and 2 parts of coarse, clean sand is 
dusted on the unhardened concrete in a uniform layer 
not over 1 in. thick. When the dry materials have 
absorbed moisture from the slab and the concrete has 
hardened enough to allow finishing, it is floated and 
troweled to unite the dust coat with the base and give 
an even surface free from air holes, depressions and other 
blemishes. The floor should be protected and cured as 
recommended for other types. This dust coat method 
of finishing should not be used for uncovered floors 
where the finish would be directly subjected to traffic. 


Wood, Linoleum, Rubber and Cork Tile 


When wood, linoleum, rubber or cork tile is to be used, 
the concrete must be thoroughly dry before cementing 
the surfacing material into place. Moisture, even in very 


small quantities, will eventually lead to the decomposi- 
tion of the adhesive. A simple test to determine whether 
or not the concrete is dry may be made by laying pieces 
of linoleum at several places on the floor, weighting 
them down so they will have uniform contact with the 
surface. If after 24 hours moisture appears on the under- 
side of the linoleum, it will be necessary to let the con- 
crete dry further before cementing the covering to it. 
The directions of the manufacturer of the materials 
being used should be followed. 


Carpet 


Floors to be covered with carpet require wood nailing 
strips, usually around the border of the area. These 
should be well seasoned lumber, dressed to 1x2 in. and 
embedded in the unhardened concrete. Special snap 
inserts are sometimes embedded in the concrete instead 
of nailing strips. In this case fastening devicesare attached 
to the underside of the carpet. 

The surface of the concrete floor should be screeded 
and troweled flush with the tops of the wood strips and 
should present a smooth, even surface. It should be 
cured and allowed to dry before placing the carpet. Pads 
or cushions under the carpet prolong the life of the car- 
pet and assist in producing soundproofness. 


REPAIRS, MAINTENANCE AND TREATMENT 


LOORS are sometimes so poorly built as to be wholly 

inadequate for the service intended. In such cases 
it is advisable to remove the defective top surface and 
replace it with a new one in accordance with the sug- 
gestions given previously. Failure to observe some fun- 
damental requirement in construction may result in 
certain defects which often can be corrected by proper 
treatment or repairs. 


Dusting 


Floor finishes that dust under service may usually 
be improved by one of the hardener treatments discussed 
on page 23. Whether the hardener treatment will entirely 
stop dusting will depend on the construction methods 
used and the resulting condition of the surface. 

Where there is a thin layer of soft, chalky material 
at the surface, this may often be removed with pads 
of steel wool attached to a scrubbing machine. After 
removal of this material, the surface should be thor- 
oughly cleaned, then allowed to dry and one of the hard- 
ener treatments applied. In other cases, it is necessary 
to grind the surface before treatment. 


Cracking 


Cracks in concrete floors may be classified as (1) struc- 
tural cracks originating in the base and extending through 
the finish, and (2) cracks confined to the wearing course. 
The latter may extend through the wearing course, or 
may be of a superficial nature, ordinarily called hair 
cracks or crazing. 

Structural cracks may be caused by shrinkage, tem- 
perature changes or settlement. If there is recurrent 
movement, there is little that can be done other than 
to keep them filled with a mastic material. Crazing 
cracks may be removed by grinding if they are not too 
deep. The only other method of removing them is to 
remove the affected area and replace it with new material. 

In many cases cracks may be filled with varnish or 
resin. Although they will remain visible, accumulations 
of dirt and leakage will be prevented. Artificial resins 
such as Cumar (available through paint and varnish 
manufacturers) may be used. This should be powdered 
and dissolved in a suitable solvent such as xylol, in the 
approximate proportions of 6 lb. of resin per gallon of 
solvent. A varnish-like material is produced which can 


2] 


be run into the cracks. Cement may be added to make 
a thicker solution for wider cracks. 

In patching concrete floors, the old wearing surface 
should be chipped off to a depth of at least 1 in., the 
roughened surface should be thoroughly cleaned of loose 
particles and should be saturated with water for several 
hours before placing new concrete. The area surround- 
ing the patch should be wetted also. The accompanying 
illustrations show correct and incorrect methods of 
patching. 


Roughened Floors 


Floors that have been improperly constructed may 
become roughened under service, or pitting may occur 
due to heavy impacts. Often such floors may be put 
into satisfactory condition by grinding off the roughened 
surface and will give good service for many years. On 
the other hand, if the concrete is of such poor quality 
that the surface will soon become roughened or pitted 
again, it would be more economical to resurface it with 
the proper quality of concrete. 


Attaching Equipment to Floors 


Theater seats, machinery and other equipment may 
be rigidly fastened to concrete floors with expansion 
bolts. For satisfactory results the concrete must be of 
such quality that it will resist the stresses developed 
by the equipment to be attached. The wearing course 
should be constructed as recommended previously. If 
large bolts extending into the base course are used, the 
base course should be well proportioned with not over 
6 gal. of water per sack of cement to provide a good 
grade of concrete. 

The usual procedure is to mark the location of bolts 
on the floor after it has hardened and cured, then drill 
the holes to the proper depth for insertion of the expan- 
sion shells. 


Maintaining and Cleaning Floors 


Properly constructed concrete floors will require little 
maintenance other than cleaning. Periodic cleaning is 
essential to durability, as grit and dirt on floors sub- 
jected to considerable traffic will be ground into the 
finish and accelerate the rate of wear. 

Floors subjected to spilled milk, syrups, fruit juices, 
brines, fats and oils and many other industrial products 
should be thoroughly scrubbed frequently. In many 
plants it is necessary to scrub the floors at least once 
a day. Warm, soapy water and stiff brushes should be 
used, after which the floor should be mopped clean. 
Electric scrubbing machines are widely used for cleaning 
large floor areas. 

Surfaces subjected to heavy trucking should not be 
allowed to accumulate a crust of dirt, as sometimes hap- 
pens in molasses, sugar and oil warehouses. Trucks ride 
unevenly over these obstructions, imposing undue impact 
stresses on the floor finish and increasing the tractive 
effort of the trucks. 

Garage and powerhouse floors frequently become soiled 


22 


INCORRECTLY INSTALLED PATCH—Patches installed 
with feathered edges will soon break down under trucking. 


CORRECTLY INSTALLED FLOOR PATCH—The chipped- 
out area should be at least 1 in. in depth with the edges 
perpendicular. 


RESULTS OF INCORRECT SCREEDING OF PATCH— 

When a patch is originally struck off to the level of the 

floor, the concrete will sag in the center, due to the fact 

that the straightedge has a tendency to cut off slightly 

below its lower edge and to the fact that the concrete 

shrinks during hardening. Additional concrete placed in 
the concave area will soon chip out under traffic. 


CORRECT METHOD OF SCREEDING PATCH—The 
strike-off board is held slightly above the level of the floor 
by strips or shims laid the length of the patch on two sides. 
For large patches the thickness of these strips will be 
greater than for small patches. The concrete is allowed to 
rest for 1 to 2 hours. This allows the concrete to attain 
some of its initial shrinkage before being troweled to its 
final plane and will result in a uniformly level surface, 
plane with the rest of the floor. 


4Boiler plate 


PROTECTION OF PATCHES—Patches should be kept con- 

tinuously wet and protected from traffic during the curing 

period. An economical method of protection consists in 

using a piece of 14-in. steel sheeting bent as shown and 

placed over the patch to take traffic during the curing and 
hardening period. 


with oil. Usually the oil has no detrimental effect if 
the concrete is properly made, but its presence detracts 
from the appearance and makes the surface dangerously 
slippery. Such floors may be cleaned by scraping off 
thickened oil crusts, then scrubbing with gasoline, tak- 
ing due precaution against fire. The floor should then 
be thoroughly scrubbed with warm, soapy water and 
mopped. The treatment will not remove stains but will 
remove the objectionable coating of oil and grease. Spe- 
cial solvents are also available for removal of oil and 
grease. 

Decorative floors should be cleaned with warm, soapy 
water prior to use and at subsequent intervals depend- 
ing on the severity of service. Only mild soaps should 
be used on terrazzo and other types of decorative floors. 
Soap should be removed by rinsing thoroughly to pre- 
vent the surface from becoming slippery. 

Terrazzo floors acquire a beautiful natural sheen when 
they are washed often for the first 2 or 3 months. After 
this period less work will be required in their upkeep. 


Surface Treatments 


The durability of concrete floors depends primarily 
upon observance of the fundamental rules in making, 
placing, curing and finishing the concrete. Dusting of 
the floor surface may occur if these rules are violated. 

Many of these floors may be improved by applying 
some material to assist in hardening and binding the sur- 
face. These treatments are not cure-alls for poor mate- 
rials or careless workmanship and will not make a perfect 
wearing surface of a poorly built floor. Magnesium fluo- 
silicate, zinc fluosilicate, sodium silicate, aluminum sul- 
phate, zinc sulphate, Chinawood and linseed oil and 
various gums, resins and paraffins are substances used 
for this purpose. Sometimes paints are applied after 
these treatments as further protection. 

It is essential that the floor be clean and free from 
plaster, oil, paint or other foreign substances before giv- 
ing any further treatment. It should also be fairly dry 
lo assist penetration. When paint of any kind is to be 
used, it is important that the concrete be absolutely dry. 


Fluosilicate Treatment 


The fluosilicates of zinc and magnesium dissolved in 
water have been used with good success. Either of the 
fluosilicates may be used separately, but a mixture of 
20 per cent zinc and 80 per cent magnesium appears to 
give the best results. In making up the solutions, 1% lb. 
of the fluosilicate should be dissolved in 1 gal. of water 
for the first application and 2 lb. to each gallon for sub- 
sequent applications. The solution may be mopped on 
or applied with a sprinkling can and then spread evenly 
with mops. Two or more applications should be given, 
allowing the surface to dry between applications. About 
3 or 4 hours are generally required for absorption, reac- 
tion and drying. Care should be taken to mop the floor 


Printed in U. S. A. 


with water shortly after the last application has dried 
to remove incrusted salts, otherwise white stains may 
be formed. 


Sodium Silicate Treatment 


Commercial sodium silicate is aboul a 40 per cenl 
solution. It is viscous and requires thinning with water 
before it will penetrate concrete. A good solution con- 
sists of 3 gal. of water to each gallon of silicate. Two 
or three coats should be used, allowing each coat to 
dry thoroughly before the next one is applied. Scrub- 
bing each coat with stiff fiber brushes or scrubbing 
machines and water will assist penetration of the suc- 
ceeding application. 


Aluminum Sulphate Treatment 


This treatment consists of one or more applications 
of solutions of aluminum sulphate. The solution is made 
in a wooden barrel or stoneware vessel and the water 
should be acidulated with not more than 1 teaspoonful 
of commercial sulphuric acid for each gallon of water. 
The sulphate does not readily dissolve and requires occa- 
sional stirring for a few days until the solution is com- 
plete. About 21% lb. of the powdered sulphate will be 
required for each gallon of water. For the first treatment 
the solution may be diluted with twice its volume of 
water. Twenty-four hours after this application the 
stronger solution may be used, and 24 hours should 
elapse between subsequent applications. 


Zinc Sulphate Treatment 


This treatment consists of the application of a solu- 
tion containing 11% lb. of zinc sulphate and a teaspoon- 
ful of commercial sulphuric acid to each gallon of water. 
The mixture is applied in two coats, the second coat 
applied 4 hours after the first. The surface should be 
scrubbed with hot water and mopped dry just before 
the application of the second coat. This treatment gives 
the floor a darker appearance. 


Oil Treatment 


Chinawood, linseed or soybean oil may be diluted 
with gasoline, naphtha or turpentine and applied with 
mops or large brushes. About equal parts of oil and 
thinner give a good mixture for this purpose and often 
a single application is sufficient. In some cases the oil 
treatment may be repeated to advantage at semi-annual 
intervals. 


Coverage 


The amounts of the above solutions required to treat 
floors will vary considerably with the porosity of the 
concrete. Generally, a gallon of any one of the solutions 
will be required for each application on 150 to 200 sq.ft. 
of floor surface. 


jyncerenee 


Sena 


iat 


4 
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PUBLISHED BY 


Portland Cement Association 


33 WEST GRAND AVENUE + CHICAGO, ILLINOIS 


ROOFS WITH A NEW DIMENSION 


ROOFS WITH A NEW DIMENSION 


Ze 

‘ SS agen y/ 

SS 
. f 


Copyright 1959 by Portland Cement Associ 


With few exceptions, the buildings conceived and executed in the past were two dimensional. 
Post-and-lintel design and construction seemed the easiest way to fill man’s eternal need for shelter. 
This type of construction has been adequate and expedient, and in many cases it still represents 
the best method of design. 

However, architects have sometimes chafed under the restraint of such planar limitations. One 
result has been the domes that dot the architecture of the past. Such variances from conventional 
design proved prohibitively expensive except where cost was relatively unimportant. 

However, in 1923 Carl Zeiss, famed German manufacturer of optical equipment, designed and 
had built the first concrete shell roof. This signaled the opening of a new era of freedom in archi- 
tectural design. In the few years since the construction of that barrel shell roof, the size, types and 
shapes of concrete shells have grown and multiplied until today there is a concrete shell roof for 
nearly every type of building. Shell roofs are now used for such divergent structures as churches, 


service stations, airplane hangars, auditoriums, industrial buildings, water reservoirs and stores. 


SHELL ACTION 


Despite their spectacular beauty, concrete shell roofs often 
prove to be the most economicéal means of roofing buildings. 
Simplified design procedures and improved forming tech- 
niques have made them highly competitive with other roof 
systems long thought to be lowest in cost. One reason for this 
surprising economy is the structural action of shell roofs. 

Shells derive their strength, and consequently part of 
their economy, from a basic and easily comprehended 
principle of statics—that form is an important factor in 
the development of strength. 

Hold a sheet of paper along one end and lift it from a 
table. It hangs limply from the points of support because 
it has practically no strength when cantilevered. Roll the 
sheet into a half-circle and hold it along one edge. Now it 
will not only cantilever but it will also support small 
weights such as paper clips. 

An analogy can be made between the flat sheet of paper 
and a beam of shallow cross-section. When straight, both 
are weak and incapable of appreciable spans because they 
resist loads by means of bending stresses only. However, 
when formed into an arc, bending forces are practically 
negated. The remaining forces acting within shells can 
easily be handled by small amounts of concrete and rein- 
foreement. Therefore, such curvilinear shapes make con- 
crete shell roofs the most efficient method known for en- 
closing space. 


If we were to accordion-pleat our sheet of paper we would 
discover that its structural strength would be increased 
much in the same manner as when curved. The depth of 
the roof and the interaction of the folds explain the great 
spanning and load-carrying abilities of folded-plate shells. 

A shell roof can be thought of as a long continuous beam 
of curved cross-section that combines the advantages of 
trusses, purlins and wind bracing through utmost inter- 
action of its parts. This ultimate achievement of mutual 
action of all parts creates unusually high lateral stability, 
which in turn imparts an unusually great capacity to carry 
unbalanced loads. The continuity which can be best 
achieved in concrete construction adds further to the effi- 
ciency of shell design. 

Engineers have successfully applied prestressing to add 
to the structural capabilities of shells. By introducing a 
prestressing force in the edge beam, in the shell itself, or 
in both, it has been possible to extend spans and increase 
load-carrying capacities considerably. 

Because of their strength-through-shape, shell roofs in 
the United States are as little as 21% in. thick. In many 
cases even this minuscule cross-section is more than is 
needed for strength. However, rigid building codes pre- 
scribe a minimum cover for reinforcement that usually 
makes 21% in. the thinnest allowable shell cross-section. 
In Mexico, shells of °%-in. thickness have been built! 


Circular dome light 


arc length 


7 Thickness 


IR 
| | “Springing line 


__Chord width 


The saving in materials for the roof, impressive though 
it is, constitutes only one of the many economies in shell 
construction. Since the weight of the roof is cut consid- 
erably, column size and reinforcement are reduced. In 
addition to these cost advantages, the smaller columns are 
architecturally more versatile. With reduced superstruc- 
ture weight, foundation loads are lowered. This is impor- 
tant where soils have unfavorable load-bearing capacities. 

The economy of any shell roof is determined largely by 
the number of times that forms can be reused. Often, 
forming costs can be reduced greatly by the use of mobile 
forms. When a concrete shell has been cast and cured, 
these forms are lowered a few feet and rolled to the location 
of the next shell to be cast. In the case of umbrella-shaped 
hyperbolic paraboloids, the forms are often made in two 
half-parts to accommodate the center column. Provision is 
made in formwork for casting the ribs as well as the shell. 

Natural lighting can easily be accomplished in shell roofs. 
Openings left between contiguous shells can be glazed with 
clear or tinted glass for effective, low-cost daylighting, 
either direct, north light or clerestory. Another method is 
to pierce the shell in several places and install either domed 
or flat fixed lights. 


Europeans initiated shell roof design and construction. 

American architects and engineers have developed these 

SHELL TYPES basic concepts and added their own ideas to create design 

and construction techniques that are both versatile and 

practical. Discussion here is confined primarily to the vast 
Tes tod architectural possibilities offered by these new roofs. 

: ] The curve, nature’s most beautiful figure, is available in 

a wealth of forms in shell roofs. They range from the clas- 

pee sical purity of a simple barrel to some highly unusual com- 

binations of dissimilar hyperbolic paraboloids. 

There are four commonly used types of shells—barrels, 

stiffening beomy J domes, hyperbolic paraboloids and folded plates. Within 
y each category are many possible variations in shape. 


BARREL SHELLS 


Barrel shells are of two types—short and long barrels. 
Long barrels are those with chord widths that are small 
compared with the span between supporting ribs. Con- 
versely, short barrels have large chord widths in Broperuon 
to the span between ribs. 

Functional requirements and architectural considera- 
tions generally are the determining factors in making the 
choice between long and short barrel roofs. For spans under 
100 ft. that require approximately uniform clearance be- 
tween floor and roof, long barrels are usually most appro- 
priate. Great room structures where vaulted ceilings are 


Long barrel shell 


Short borrel shell 


practical, such as auditoriums, churches, gymnasiums, 
concert halls, and theaters, are often best realized through 
short barrel shells. Impressive spans have been achieved 
with both types. The drawing on page 10 indicates typical 
dimensions for a group of multiple long-barrel shells of 
commonly encountered spans. 

Short barrels almost always are the architectural focal 
point in a building complex, such as a campus-type school 
or a shopping center. Their sweeping arcuate lines lend a 
commanding yet graceful character to such developments. 
In most cases, long barrels serve as auxiliary accents in 
multibuilding plans, although in sinusoidal shapes they can 
easily become a commanding element in the overall design. 

Short barrel roofs greatly reduce the need for walls since 
the ribs extend to the abutments and the shell itself may 
be terminated a short distance from the ground level. 


HYPERBOLIC PARABOLOIDS 


Mention has already been made of the rigidity achieved in 
shells by their shape. The hyperbolic paraboloid is a shape 
of double curvature; that is, its surface is curved on two 
planes. Double curvature imparts improved stiffness to 
hyperbolic paraboloid shells that increases their ability to 
span and to carry unsymmetrical loads. 

A seeming paradox characteristic of this complex shape 
accounts for its construction practicability. Despite its 


double curvature, this shape is composed entirely of 
straight lines. It is possible, therefore, to build forms with 
straight lumber. Also, reinforcement need not be bent but 
can be positioned along the straight form boards. The 
dual advantages of extreme stiffness and low construction 
cost, when coupled with the beauty and versatility of this 
shape, make it a potent force in roof design. 

Two commonly used variations of the hyperbolic parab- 
oloid shell are the saddle and umbrella shapes. However, 
the range offered by varying the rise and span of shells 
and the variety achieved in different juxtapositions of like 
or dissimilar shells create a truly unbounded choice for 
any applicatiom. 


DOMES 


Dome shells are the aristocrats of roofs. Their perfectly 
symmetrical shape and spacious, vaulted interiors inspire 
architect and layman alike. Perhaps this is why domes 
have become so popular for churches and other buildings 
of public congregation. One of the first shell roofs to capture 
the fancy of the American public was a dome—the shell 
over Kresge Auditorium on the campus of the Massachu- 
setts Institute of Technology, Cambridge, Mass. 

Domes are often the choice of the architect who wishes 
to express lightness or freedom from restraint since they 
are ribless and need touch the earth at as few as three 


points. Their uncluttered soffit and symmetrical lines 
capture and retain the attention of the occupants without 
resorting to elaborate decorativeness. 

A dome shell offers architects the closest approach man 
has yet devised to the perfect roof—a thin yet rugged slab 
of pleasing design floating in air. The last specification has 
yet to be met, but the expansive domes already built which 
dip to touch earth at widely separated points come close 
to satisfying even this unlikely quest. 


FOLDED PLATES 


Folded-plate shell roofs are noted for their amazing span- 
ning and load-carrying capabilities. In hangar construction 
they have been used to accommodate the great wingspans 
of jet aircraft. Their ability to cantilever has also been 
capitalized upon in schools, stores and industrial buildings. 
In two-story buildings, the second-story floor slab can often 
be suspended from a folded-plate roof. 

There are three basic types of folded-plate shells— 
V-shaped, Z-shaped and a modified W-shape. An example 
of the W-shape can be seen in the photographs of Sears, 
Roebuck & Co., Tampa, Fla. (see page 14). As in hyper- 
bolic paraboloids, these three forms of the folded plate can 
be varied in many ways. 

Folded-plate shells, in common with all shell roofs, are 
essentially modified beams. For example, the Z- and W- 


shaped types are similar to the ubiquitous I-beam except 
that flanges are offset to alternate sides of the centerlines 
of the webs. The great separation of flanges and the en- 
hanced continuity of action between neighboring shells by 
the sloped web account for the strength of this shell. 


A CHALLENGE 


10 


More than any other roof type, concrete shells hold up a 
challenge to the imagination of architects. Little has been 
done in combining shells of different shapes or in combin- 
ing shell types—for example, the barrel and the folded 
plate. Shells have proved themselves capable of striking 
feats in beauty, economy and spanning ability. Engineers 
have simplified their design and construction. Now the 
American architect has the creative challenge of broaden- 
ing the application of shell roofs. It’s a responsibility. But 
with the responsibility comes an unequaled opportunity. 


: 
160. 45 16 , : 


in. 
ae 


Table 1. Typical long span multiple barrel dimensions. 


FOREIGN 


Ree Oe ew Ny 


Be 8 Sai he 5 


Centre National des Industries 
et des Techniques, Paris, France 
Batir-Delaporte-Frechon photograph 


This largest roof in the world isa 
double shell that spans 720 ft. along each 
of its three sides and covers 5% acres. 


12 


La Iglesia de los Virgen Milagrosa, 
Mexico City, Mexico 


Hyperbolic paraboloid shells 
create a modern and yet gothic-like 
vaulted roof for this church. 


_ roof this large industrial building. 


Brynmawr Rubber, Ltd., 
South Wales, England 


Nine 83x64-ft. dome shells, pierced for 


circular skylights, and multiple-barrel shells 


St. Francis de Sales High School, Chicago, Ill. 
Architect-engineer: Belli and Belli, Chicago, Ill. 
General contractor: Fred Berglund and 

Son, Inc., Chicago, III. 


A long barrel shell 4% in. thick covers 
15,000 sq.ft. of column-free floor area in this 
gymnasium. Circular skylights 

reduce the artificial lighting requirements. 


AMERICAN 


Gries 


Crossroads Restaurant, Dallas, Texas 
Architects-engineers: O'Neil Ford, Richard S. Colley, 

A. B. Swank, S. B. Zisman, 

Associated Architects & Planners, Dallas, Texas 
Consultant: Felix Candela 

General contractor: Great Southwest Corp., Dallas, Texas 


Skylights and other perforations offer 

no structural or construction problems 
because shells characteristically have low 
stresses and omnidirectional 


load distribution. 
13 


Sears, Roebuck and Co. Store, Tampa, Fla. 

Architect: Weed, Russell, Johnson and Associates, Miami, Fla. 
Engineer: Norman Dignum, Tampa, Fla. 

General contractor: Frank J. Rooney, Inc., Miami, Fla. 


Shown here is a striking folded-plate shell roof 

that covers 163,715 sq.ft. of floor area with only 

a single row of 16 intermediary columns 

bisecting the building. The drawing shows how 

it was possible, because of the shell’s great strength, 
to suspend the second story floor slab from the roof. 


Ralph's IGA Grocery Store, Wichita, Kan. 
Architect: Vanlandingham and Hanney, Wichita, Kan. 
Engineer: G. Hartwell & Co., Wichita, Kan. 

General contractor: F. H. Sell Construction Co., Wichita, Kan. 


Nine 40x40-ft. hyperbolic paraboloid shells provide 
an eye-catching, low-cost and fire-resistant roof for this store. 


14 


— 
tees 


Bowl Mor Bowling Alleys, Colorado Springs, Colo. 

Architect: Toll and Milan, Denver, Colo. 

Consulting engineer: Ketchum and Konkel, Denver, Colo. 

General contractor: Holmgren and Larson, Colorado Springs, Colo. 


A folded-plate roof provides the necessary column-free 
floor area for this attractive bowling alley. 

The multiple surfaces assist in noise reduction 

and conceal lighting fixtures. 


St. Gertrude’s Church, Franklin Park, Ill. 
Architect: Belli and Belli, Chicago, Ill. 
Engineer: Edmund Charchut, Chicago, III. 


General contractor: Frank Burke and Son, Inc., Chicago, III. 


The roof plates combined with the upper walls 

of the nave constitute a folded-plate shell in this church. 
The transverse roof span is 30 ft., but the cant of the 
walls provides a 38-ft. wide clear area at floor level. 


Texas Instruments, Inc., Dallas, Texas 

Architects-engineers: O'Neil Ford, San Antonio, Texas 

Richard S. Colley, Corpus Christi, Texas 

Associates: A. B. Swank, Dallas, Texas, S. B. Zisman, San Antonio, Texa 
General contractor: Robert E. McKee, General Contractors, Inc., 

Dallas, Texas 


Bays 63 ft. wide provide utmost space flexibility 

in this hyperbolic paraboloid roofed industrial-office buildin 
Each roof unit is composed of four saddle-shaped shells 
joined at the top to form straight ridges. 


| May-D&F Company Department Store, Denver, Colo. | 


iS ; . Lambert-St. Louis Municipal Airport Building, St. Louis, Mo. 
prebitectsl. 7a ra og tay Ss nee vor Ne Architect: Hellmuth, Yamasaki and Leinweber, St. Louis, Mo. 

MOINS AC DENS ANC CHACler, INOWY OL Ka Nace | Structural engineer: William C. E. Becker, St. Louis, Mo. 
General contractor: Webb and Knapp Construction Corp., New York, N.Y. | 


(} Consultants on shell design: Roberts and Schaefer, Chicago, III. 
k General contractor: L&R Construction Co., St. Louis, Mo. 
| 


Four saddle-shaped hyperbolic paraboloids constitute an unusual 
and commanding portal for this store. Covering an area 113x 132 ft., | Intersecting barrel shell segments form the graceful roof of th 


it illustrates but one of the multitude of possibilities | 415x123-ft. airport building. Skylights are provided 
for combining shells to create an architectural focal point. & at the junctures of the three dome-like roof sections. 


16 


Casey Junior High School, Boulder, Colo. 
Architect: H. D. Wagener, Boulder, Colo. 

Engineer: Ketchum and Konkel, Denver, Colo. 
General contractor: Johns Engineering, Denver, Colo. 


Inside and outside, the Z-shaped 
folded-plate roof of this combination 
girls’ gymnasium and cafeteria 

serves several functions. Clerestory 
lighting, a column-free interior, 

firesafe construction and acoustical 
control by the action of the baffled 
ceiling are some advantages folded 
plates offer for this type of construction. 


Kresge Auditorium, Cambridge, Mass. 
Architect: Eero Saarinen and Associates, 
Birmingham, Mich. 

Associate architect: Anderson, Beckwith & Haible, 
Boston, Mass. 

Engineer: Ammann & Whitney, New York, N.Y. 
General contractor: George A. Fuller, Boston, Mass. 


The widely-publicized shell dome 

on the Massachusetts Institute 

of Technology campus is an equilateral 
spherical triangle, one-eighth 

of a sphere. The three supports at 

the vertices of the triangle 

are 160 ft. apart. 


Alabama State Coliseum, Montgomery, Ala. 
Architect: Sherlock, Smith and Adams, 
Montgomery, Ala. 

Engineer: Ammann & Whitney, New York, N.Y. 
General contractor: J. A. Jones Construction Co., 
Charlotte, N.C. 


Bids received for the short barrel 
shell of this coliseum illustrate 

the economy of shell roofs. Despite 
a springing line 50 ft. from ground 
level which necessitated greater 
falsework and permitted only five form 
re-uses, the two lowest bids were 

in concrete. In addition, construction 
time was cut 30 per cent below 

that required for the alternate 
construction material. 


Central Supply Center, Seattle, Wash. 

Architect: John W. Maloney, Seattle, Wash. 
Engineer: Worthington and Skilling, Seattle, Wash. 
General contractor: Howard S. Wright and Co., Inc., 
Seattle, Wash. 


This large, L-shaped warehouse has a long 
barrel shell roof formed by using two 33x128-ft. 
forms to cast all 14 of the shells. 


18 


Freedom Public School, Freedom, Okla. 
Architect-engineer: Jack L. Scott and Associates, Oklahoma City, 
General contractor: Rose Brothers, Alva, Okla. 


Chord widths for the barrel shells 

of this school were made the same as classroom 
widths to minimize partition heights. 

Overhangs provide a pleasing architectural 
feature and reduce glare in the classrooms. 


Elks Club, Duncan, Okla. eee 
Architect: Cottingham & Cook, Lawton, Okla. 
Engineer: Kirkham, Michael & Associates, Oklahoma City, Okla. 
Contractor: The W. C. Shelton Co., Lawton, Okla. 


A hyperbolic paraboloid roof lends drama 

to this two-story clubhouse. The upward slanting 
projections of the shell cantilever over 

and protect the second-story veranda. 


Tradewell Market, Burien, Wash. 


Architects-engineers: Welton Becket and Associates, Los Angeles, Calif. 
General contractor: Jentoft and Forbes, Seattle, Wash. 


A 12-ft. cantilever of the 2%4-in. thick 

barrel shell covering this grocery store provides 
a walkway and loading area sheltered from 
inclement weather. This distinctive roof type 
has been adopted as this firm's trademark. 


19 


33 West Grand Avenue, Chicago 10, Illinois 


The activities of the Portland Cement Association, a 
national organization, are limited to scientific research, 
the development of new or improved products and 
methods, technical service, promotion and educational 
effort (including safety work), and are primarily designed 
to improve and extend the uses of portland cement and 
concrete. The manifold program of the Association and 
its varied services to cement users are made possible by 
the financial support of over 70 member companies in 
the United States and Canada, engaged in the manu- 
facture and sale of a very large proportion of all portland 
cement used in these two countries. A current list of 
member companies will be furnished on request. 


Printed in U.S.A. 


Ss9 


CONCRETE 


for industrial 


buildings 


and garages 


a £ 
NF 


PORTLAND CEMENT ASSOCIATION 
33 West Grand Ave. - Chicago 10, Il. 


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CONCRETE 


for 


INDUSTRIAL BUILDINGS 


and 


GARAGES 


The activities of the Portland Cement 
Association, a national organization, are 
limited to scientific research, the develop- 
ment of new or improved products and 
methods, technical service, promotion and 
educational effort (including safety 
work), and are primarily designed to 
improve and extend the uses of portland 
cement and concrete. The manifold pro- 
gram of the Association and its varied 
services to cement users are made possi- 
ble by the financial support of over 70 
member companies in the United States 
and Canada, engaged in the manufacture 
and sale of a very large proportion of all 
portland cement used in these two coun- 
tries. A current list of member companies 
will be furnished on request. 


Published by 
PORTLAND CEMENT ASSOCIATION 
33 West Grand Avenue, Chicago 10, Illinois 


Bags of sugar stacked nearly to the ceiling in the Wm. Wrigley Jr. Company plant, Chicago, illustrate the ability of flat slab concrete 
construction to carry extremely heavy loads. 


Copyright, 1946 by Portland Cement Association 


Section 


I 
Pig 
3. 
4 
5) 


6. 
tie 


TABLE OF CONTENTS 
INDUSTRIAL BUILDINGS 


Title Page 
Introduction . : ; ; 5 
Concrete floors on fill Ss ee % 
Floor framing . é aio 
Choice of floor framing . 10 
Diagonal arrangement of columns . > 12 
Live load, story height, building width _. : 14 
Floor finishes . ; 14 
SALTS pee, Se es (a8 17 
Walls . : ; 5 PAU 
Roofs ’ ; : 23 
Fire resistance requirements _ . 20 
Design for additional stories . , 27 
Details for additional stories _. ; . 28 
Extension of buildings —. ; ; 29 
Expansion anchors : . rol) 
Inserts. ; , 31 
Pipe sleeves in new concrete floors . : : ap BY! 
New holes through old concrete slabs , 33 
Installation of electric circuits . ; ; . d4 


GARAGES 


Dimensions of automobiles _. ; : 39 
Layout of parking units __. ; 8S 
Framing plans _. : ' ' 36 
Ramps : : . / : . 38 
Structural details —. ; 39 


Elevators, stairs, roofs . ' ; ; . 40 


Weaving building at Danville, Virginia, has five bays of flat slab construction. 
surfaces, exposed electric circuits, and sprinkler pipe arrangement. The entire | 
abundant light. Built by Aberthaw Construction Company. 


FOREWORD 


| is a right and a wrong way to 

do almost everything. Frequently the 
right way is the simplest and most eco- 
nomical, but not always the most obvi- 
ous. Some of the information presented 
here will be well known to many and 
some of it only to the few who through 
experience have learned the best way to 


secure desired results. 


Industrial planning has reacheda high 
stage of development, but the designer 
of industrial buildings is still confronted 


with numerous problems affecting the 


economy, safety and serviceability of 
the buildings themselves. This booklet 
has been prepared to supply information 
which will aid in solving some of those 
problems especially pertaining to con- 


crete construction. 


It has not been possible to cover all 
subjects exhaustively within these pages, 
so reference is made to numerous other 
Portland Cement Association publica- 
tions, augmenting the material pre- 
sented. These publications will be fur- 
nished free on request in the United 


States or Canada. 


PORTLAND CEMENT ASSOCIATION 


The drawings in this publication are typical designs and should not be used as working drawings. They are in- 
tended to be helpful in the preparation of complete plans which should be adapted to local conditions and should 
conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. 


Attention is called to large windows, painted concrete 
ayout has a distinct note of simplicity, cleanliness and 


INDUSTRIAL BUILDINGS 


1. INTRODUCTION 


QNLY a few decades ago, little thought was given to 

layout of factory buildings. The usual procedure 
was to determine the area of floor space necessary and 
to enclose that space by walls and a roof. In those days 
most structures were of the wall-bearing type with large 
piers and deep spandrels between small windows, with 
dark work rooms and unsanitary floor construction that 
often needed costly maintenance. The buildings were 
not only costly to maintain but also expensive to oper- 
ate. From the viewpoint of operation, many of them 
were practically useless before they had produced the 
anticipated return on the investment. 

Keen competition and rising production costs just 
prior to 1920 impressed upon factory owners the neces- 
sity for careful planning, and during the period that has 
followed emphasis has been laid on reduction of operat- 
ing costs and improvement in building construction 
toward that end. Many building types and details have 
been tried. Some that have proved most satisfactory are 
assembled and discussed here. 

A factory may be defined as premises where raw or 
partly manufactured materials are converted into a 
finished product. The procedure requires expenditure of 
labor, power, heat and light. In the old-time factory, 
one noticed a lack of system, a waste of man power, and 
backward conditions resulting from insufficient plan- 
ning. Power, heat, up-keep and insurance rates were 
high, and new manufacturing processes seldom fit into 
old buildings. In contrast, the modern factory building 
must be operated at costs for maintenance, insurance, 
labor, power and heat which are reduced to the lowest 
level consistent with efficient performance. 

In designing modern factories, particular considera- 
tion must be given both to departmental planning and 
to structural layout. Departmental planning has devel- 
oped into a subject of considerable scope, on which 
numerous publications are now available. This text, 
therefore, will be confined to the specific details related 
to structural layout especially in so far as they are used 
in the types of reinforced concrete construction which 
have been developed and used so extensively during the 
past few decades. A distinction is made between manu- 
facturing plants and commercial garages, but it is in 
reality impossible to draw a sharp boundary line be- 
tween them. Much of what is said about manufacturing 
plants applies equally well to construction of ware- 
houses and storage buildings. 


In the discussion that follows, details of floor con- 
struction, stairs, walls and roofs are presented, followed 
by general planning for additional stories, extensions to 
the building and installation of electric circuits. The 
last six sections of the booklet deal with special problems 
relating to garages. 


2. CONCRETE FLOORS ON FILL 


Concrete floors on subsoil in basements of multi-story 
buildings and the ground floors in one-story buildings 
are essentially the same. Details will be presented for 
basement construction but they also apply in principle 
to ground floor construction. The average ground water 
level at the building site is usually below the slab, and 
this condition will be illustrated first. 

Fig. 1 illustrates how the subsoil is first leveled and 
then covered with a layer of cinders or gravel. After the 
fill has been compacted, the basement slab is cast on 
top of it. Drainage of the basement, if required, may 
be provided by pitching the floor surface to a drain 
outlet. The fill below the floor may be drained by means 
of concrete tile laid as illustrated at the wall footing. 


SJOINT FILLER 


BASEMENT [..-%. MOP COAT OF TAR OR ASPHALT 
pa 5" CONC. SLAB 
PS MEERA TS 3°?-10"0.C 
es ; BOTH WAYS 
SOR CINDER OR 
G" DRAIN TILE GRAVEL FILL 


Fig. 1. Concrete slab on fill showing detail at wall footing. 


The slab seldom needs to be more than 5 in. thick 
reinforced with 34-in. round bars spaced 10 in. on 
centers extending in both directions*. Particular atten- 
tion should be given to the joint between slab and wall 
footing. The detail in Fig. 1 shows a mop coat of tar or 
asphalt on the ledge of the wall footing and a 4-in.- 
thick joint filler inserted between edge of slab and inside 
face of wall. This detail is recommended because it 
breaks the bond between the slab and wall and permits 
some relative movement between them, whether it be 
due to volume change or settlement. It also has the 


*Floors on the ground can be constructed without reinforce- 
ment when properly designed as plain concrete slabs and ade- 
quate provision is made for shrinkage and expansion. Design and 
construction data are given in Concrete Floors on Ground avail- 
able free in the United States and Canada on request to Portland 
Cement Association. 


advantage of insuring watertightness in the joint if the 
water level is near or slightly higher than the level of 
the floor. Where any appreciable head of water is antici- 
pated, a metal water stop should be incorporated in 
the joint. 

At interior columns, the basement slab is generally 
laid on top of the footing cap as illustrated in Fig. 2. 


COLUMN 
BASEMENT SLAB 
( 3-2°> AROUND COLS. 


ee pees 22a 3 - 


es a FILLER 
“]/ -TAR OR ASPHALT 


en 


FOOTING 


Fig. 2. Conerete slab on fill showing detail at column 
footing. 


A mop coat and a joint filler are recommended at in- 
terior columns for the same reasons as for wall footings. 
Extra reinforcement is placed in the slab adjacent to 
the column in order to minimize cracking that other- 
wise may extend from the edges of the hole through the 
basement slab. 

The top of footing caps may of course be below the 
bottom of the slab, and in this instance the mop coat is 
unnecessary but the joint filler and the extra reinforce- 
ment remain as shown in Fig. 2. 


COLUMN 
*: 


BASEMENT 


Fig. 3. Arrangement of dummy joints in slab on fill. 


Fig. 3 illustrates a basement slab laid on fill with a 
Y4-in. joint filler placed along the wall and around the 
columns. Some slabs have shown a tendency to crack 
along the column centerlines. The cracks entail no 
hazards but may be unsightly. They may be confined to 
certain positions and concealed by means of “dummy” 
joints placed on column centerlines. The dummy joint 
in this design is a }4-in.-deep “‘cut”’ in the floor surface. 
It may be used with even better result if the dummy 
joint is also a construction joint as shown in Fig. 4. 
As an additional precaution to make sure that cracking 
will not occur outside the joint, part of the reinforce- 
ment may be stopped at the joint and a wood strip 
provided at the bottom of the joint. Cracks in the 
joints are straight and concealed in the bottom of the 
groove. If desired the groove may be filled with mastic. 


6 


+“ DEEP CUT FILLED. 
WITH MASTIC 


z RRP, Sarr 
puee tise eee item 
ae OR 


$°6@10°0.C. CONTINUOUS 
| ACROSS JOINT 


SS, A O77 
ONE-HALF OF BARS 
DISCONTINUED HERE 


Fig. 4. Detail of dummy joint. 


me CONSTRUCTION JOIN 


If the floor is to be insulated, the construction in 
Fig. 5 is recommended. The subsoil is first made level 
and compacted. A 2-in. concrete base is then laid on 
the subsoil and brought to an even surface which is 
mopped with tar or asphalt before the insulation mate- 
rial is laid on it. The slab on top of the insulation is 
reinforced and otherwise constructed as though it were 
placed directly on the ground. 


BASEMENT SLAB WATERPROOF INSULATION 


TO | 


Sera Gee eyo oe OR yf 2 


Bis PETS 1s Om SR ee rig tn ae ees ee Te ES 
i, 


~ 
(Ae 


MOP COAT OF 
TAR. OR ASPHALT 


WR 
ExS LAB 


ONCR 


EREMBAS 


Fig. 5. Insulated concrete slab on fill.9 $3 fF! 


The construction details described for basement 
slabs apply where the average level of the water table 
is even with or below the slab. If it is much higher, the 
ground water will exert an upward pressure—hydro- 
static pressure—upon the bottom of the slab. In such 
instances, the slab should be designed as an “inverted” 
floor slab. Since the basement slab is “‘supported”’ on 
walls and columns, a flat slab construction*—suitably 
modified—is the natural solution. One type of layout is 
illustrated in Fig. 6 which shows the basement slab 
extended past the walls and under the columns. The 


2"CONC. BASE SLAB 


Fig. 6. Basement slab designed for hydrostatic pressure. 


extra depth of slab under columns serves as the “drop 
panel” for the flat slab construction. A waterproof 
membrane envelops the basement and is protected by 
a 2-in. base slab on the bottom and by portland cement 
plaster on the vertical surfaces. Another type of 
layout for basement slabs subject to hydrostatic pres- 


*For further details, see Section 3: ‘Floor Framing”’. 


+. 0° COM ob nee? 


Reinforced concrete ribs carry the roof and a great deal of equipment in the beef house at Armour and Company plant in Chicago. The 
ribs may be described as “‘rigid frames with arched deck’’. A construction view of a rib is shown in another photograph. Designed by the 
engineering department of Armour and Company. 


CEMENT PLASTER 
PROTECTION 


WALL 


COLUMN 


BASEMENT SLAB | 
WATERPROOF MEMBRANE 


CO. ee ola cna oar. 


BCCONC 


Pe Came en 
NO DOWELS BASE, PILE CAP OR CAISSON 
THROUGH MEMBRANESO2 yg OK 


>) 


Fig. 7. Basement floor and walls with waterproof mem- 
brane, columns supported on pile caps or caissons. 


EXTRA BARS 
BASEMENT SLAB | AROUND OPENING 


Sep Renee “oy Tae 


WATERPROOF 
MEMBRANE 


Fig. 8. Detail at sump in basement. 


sure is illustrated in Fig. 7. In this case, the water- 
proofing membrane is laid on top of the mat, cap or 
caisson supporting the column. No dowels should ex- 
tend through the membrane. 

For prevention of leakage at “‘sumps’’ or drainage 
pits in basements, the detail shown in Fig. 8 is used. 
Note that the membrane around the sump and under 
the basement slab is made continuous and that extra 
reinforcement is provided in the basement slab around 
the sump opening. 

Typical connection details are shown in Fig. 9 for 
pipes extending through basement walls. The special 
wall pipe fitting shown may be made even more water- 
tight if provision is made for a joint that can be calked. 


4 
CAULKED WITH 
OAIKUM 


5"TOZ" JOINT 7 [ie a3 


Fig. 9. Details of pipes extending through basement wall. 


7 


3. FLOOR FRAMING 


The majority of reinforced concrete floors in multi- 
story factory buildings is of the type called “‘flat slab” 
or ‘mushroom system’’. For illustration, during a 
period of twenty-five years since 1918 the Eastman 
Kodak Co., Rochester, New York, constructed 4,550,000 
sq. ft. of floor area in buildings of reinforced concrete, 
and nearly 78 per cent of the concrete used was in 
buildings having flat slab floors. 

The dimensions of column caps and dropped panels 
shown on the typical flat slab framing plan in Fig. 10 
are those given in standard codes for the so-called 
“ceneral case”’ of flat slab construction. 

A building may be provided of greater width than that 
in Fig. 10—without increasing the panel size—by using 
the layout illustrated in Fig. 11. The flat slab floor in 
Fig. 11 is cantilevered beyond the exterior columns, 


= ANGLE NOT LESS THAN 45°— 


SECTION A-A 


Fig. 10. Flat slab framing plan. 


SEG OND SS 


and the end of the cantilevered floor supports spandrel 
wall and window sash. There are no columns or pilasters 
in the walls of a building with this type of framing, so 
the glazing can be continuous. The advantage of having 
continuous glazing can also be gained by having the 
wall placed just outside the exterior columns. 


Framing around large openings may conveniently be 
made as illustrated in Figs. 10 and 11. The “beams” in 
Fig. 10 have a depth equal to the combined depth of 
slab and drop panel, which leaves the same clear height 
below the beams as elsewhere below drop panels in the 
same story. This simplifies the installation of pipes, 
shafting and flues on the ceiling. 


The framing at the openings in Fig. 11 illustrates the 
use of beams with webs of ordinary shape and depth. 
This type of framing is not as economical as that in 
Fig. 10 because the deeper beam webs cut into the 
forms at columns. Both types of framing, however, are 
adequate and are commonly used. 


Small openings may be placed in flat slab floors with- 
out making any special provision for framing around 
them. Reinforcement interrupted by such openings 
should be replaced by additional reinforcement of like 
amount placed along the sides of the opening. Referring 
to the upper left hand corner of the framing plan in 
Fig. 11 in which the customary ‘‘strips’’ used in flat 
slab design are shown, “‘small’’ openings may be de- 
scribed as those falling within the following maximum 
dimensions: 


In “‘middle-middle” areas, openings not to be 
larger than one-half of the panel dimension 
in either direction. 

In “‘middle-column”’ areas, openings not to be 
larger than one-eighth of the panel dimen- 
sion in either direction. 

In “‘column-column”’ areas, openings not to be 
larger than one-twentieth of the panel 
dimension in either direction, and not more 
than one opening at each column. 


Openings larger than those described are also per- 
missible under some codes without special framing 
around them, if provision is made for the total positive 
and negative resisting moments. 

Cross-sections of columns in Fig. 10 are shown square 
in walls, but a rectangular cross-section is substituted 
for the square one when required in order to make the 
clear width between wall columns equal to dimensions 
of one of the standard window sash. 
Interior round columns are cast in 
forms made of sheet metal. In general, 
the diameters should be in even inches 
for column shafts and in whole and half 
feet for column capitals. 

Marginal beams may be made wide and shallow as 
illustrated in Fig. 10. The beam width is optional, but 
it is often desirable to make the width uniform through- 
out. The form construction is then simplified, and the 
straight offset in the ceiling just inside the wall makes 
a convenient place for installation of a metal casing 
with removal cover designed to carry electric con- 


COLUMN 
STRIP 


STRIP 


MIDDLE 


COLUMN 
STRIP 


“COLUMN MIDDLE COLUMN 


sale | Siem es inte ! 


duits. It is recommended not to carry window sash all 
the way down to the floor, but to stop it at a sill about 
3 ft. above the floor. Window sash below this level adds 
little or nothing to the illumination and is subject to 
breakage. 

Many factory floors are framed as illustrated in Fig. 
12, in which the column layout is identical with that 
for flat slab framing in Fig. 10. The floor is a solid con- 
crete slab with reinforcement extending in two direc- 
tions, and each slab panel is supported by beams on 
all four sides. 

It has been customary to construct the beams with 
the ordinary type of deep webs; but the shallow, wide 
webs illustrated in Fig. 12 have several advantages, 
especially for factory buildings. Column forms are 


ISOMETRIC VIEW OF BOTTOM OF 


SECTION A-A FLOOR FRAMING 


Fig. 12. Two-way solid slab framing plan, 


| ee 
ay 


SECTION B-B 


= Fig. 11. Flat slab framing with floor cantilevered at 
walls. 


simpler to construct since they are usually of plain 
prismatic shape without any beam cuts.* The slab span 
may be taken as the clear distance from face to face of 


*In some cases, i.e., where there are large unsymmetrical live 
loads, it may be necessary to haunch the beams in order to 
transmit the moment into the columns. 


—-5 ---—- 
ae | aes 


| 
LJ 


beam webs and is therefore reduced when the web is 
made wider. Shallowness of the beam webs facilitates 
the installation of sprinkler pipe and other ceiling 
equipment, and the shallow webs cast but little shadow 
on the ceiling which therefore gives good reflection of 
daylight from the windows. 

When solid two-way slab framing has wide, shallow 
beams it is in many respects similar to a flat slab fram- 
ing not only in structural action but also in regard to 
performance. The formwork is simple and the ceiling 
presents a flat surface for attachment of equipment. 
Both types possess admirable sturdiness and ability to 
carry heavy loading and vibrating machinery. The 
shallowness of two-way floor construction with wide 
beams reduces story height which results in lower cost 
of walls, columns, elevators, stairs, pipes and ducts. 
The large flat ceiling surfaces provide excellent reflec- 
tion of light, especially when painted white, and good 
illumination is essential in factory buildings. 

The type of concrete floor illustrated in Fig. 13 known 
as “‘beam and girder’ framing, is well suited to condi- 
tions in factories. A slab thickness of 41% in. including 
concrete finish is sufficient for the best type of fire 
resistant structure.* There is generally a beam on each 
column centerline across the building and two inter- 
mediate beams. 

The floor in Fig. 13 is shown cantilevered beyond the 
exterior columns. This serves to reduce the beam span 
and makes it possible to take advantage of continuity 


*See Section 11: “Fire Resistance Requirements’’. 


over exterior columns, thereby reducing both the col- 
umn and beam moments as compared with the more 
conventional layout with columns in the exterior wall. 
Neither the cantilever nor the regular column layout 
shown are essential features of “beam and girder” 
framing, of which there are many modifications. In 
fact, one of the advantages of ““beam and girder’ fram- 
ing is its adaptability to irregular column layouts. 

Openings may be provided almost anywhere outside 
the webs without changing the framing. Ceiling inserts 
for attachment of equipment are generally placed in 
soffits of webs. 


4. CHOICE OF FLOOR FRAMING 


Three types of floor framing commonly used in fac- 
tory construction have been illustrated and described 
in Section 3. The designer making a choice of floor 
framing for a specific job will consider numerous items 
which may be classified in the three groups: architec- 
tural layout, structural requirements, and cost. 

Important items in connection with architectural 
layout are openings for stairs, elevators, chutes, ramps, 
or for mechanical equipment extending through more 
than one story. It is possible that the number, size and 
arrangement of openings may cut up the floor slab to 
such an extent that a beam and girder layout becomes 
the best choice. In other instances, one or more col- 
umns must be omitted or offset and hence require the 
use of long span girders or transfer girders. Variations 


: My ait 


[1 | 
[ee ee ee eee 
es 


VA 
NV a a ee ee 


aa So ae (SS SS SSS SSS 


em oe 

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Se re val ae el 


SECTION A-A 


SEGHIONSBSE 


Fig. 13. Beam and girder framing. 


in floor level in the same story, depressions or pits in 
the floors together with other similar details, all tend 
to interfere with the economical layout of flat slab. In 
such cases, there is advantage in using metal pan and 
girder framing for light loadings or beam and girder 
framing with solid slab for heavier loadings. These 
floor types also give a satisfactory solution to the fram- 
ing problem where the column arrangement is irregular, 
as for example, where the column spacing is much 
greater in one direction than in the other. If the ratio 
of long to short span of a panel is gradually increased 
beyond one and one-half, both flat slab and two-way 
slab framings lose much of their economic advantages. 


Structural requirements that have an important 
bearing upon choice of framing include, first of all, the 
type of loading. The lighter the superimposed loads the 
more economical will be a metal pan floor slab sup- 
ported on beams or girders, while the flat slab will show 
more economic advantage for heavier loads. The beam 
and girder framing with a solid slab occupies an inter- 
mediate position. For support of vibrating loads, floors 
with a considerable amount of dead load are especially 
well suited, and slabs reinforced in two or in four direc- 
tions are often preferred for support of large concen- 
trated loads. The designer must often give thought to 
the relative economy of floor framing types as they are 
influenced by the structural requirements in municipal 
or other building codes. For illustration, design re- 
quirements for two-way solid slab may differ in two 
codes with the result that this framing compared with, 
say, flat slab may be more economical in one case than 
in the other. The choice of framing may likewise de- 
pend on whether or not it is necessary to design the 
structure for hurricane exposure and earthquakes. It is 
possible that horizontal loading may require that ver- 
tical bents be designed as rigid frames composed of 
columns and beams or girders. If so, a beam and girder 
framing is preferable, and the girders should be deep 
rather than shallow. 


The question of cost is a major consideration during 
practically the entire period of planning and designing. 
One of the very first functions the designer frequently 
performs is to advise the owner on the shape, type and 
general arrangement of the structural layout which can 
be built and operated at the lowest cost and yet fulfill 
the industrial requirements. This problem must be con- 
sidered before drawing formal plans, and other related 
studies must be carried out beyond that period. The 
customary procedure followed in making cost studies 
will be discussed briefly. 


First of all, the designer investigates problems in 
regard to width and height of structure to be built as 
well as to spacing of columns or size of panels. Import- 
ant factors influencing the choice of width of building 
are requirements for day lighting, as discussed in Sec- 
tion 3, and also cost of wall construction in terms of 
dollars per cubic foot of volume of the building. This 
unit cost of wall decreases with increasing width, but 
for factory buildings, the rate of decrease becomes 
small for widths in excess of approximately 80 ft. 
Widths less than approximately 60 ft. are not economi- 


Flat slab with a long opening for a skylight placed along the middle 

of a bay makes an excellent roof construction in the Walgreen 

Company plant in Chicago. The flat slab is cantilevered beyond 

the adjacent columns and extended to support the edge beam 
around the skylight. Designed by A. Epstein. 


cal from the viewpoint of unit cost of wall construction. 
If the shape of the building plan differs from a rectangle, 
the question of unit wall cost must of course be studied 
carefully. The effect of building height upon cost is not 
generally very pronounced for structures between three 
and eight stories high. From eight stories up, the cost 
per cubic foot rises, but rather slowly. However, it is 
difficult to give general rules because factors such as 
type of foundation and requirement as to wind pres- 
sure design may be important variable elements in the 
cost analysis. 


The spacing of columns cannot be chosen solely on 
the basis of cost analysis. In garages, for illustration, 
fairly uniform standards exist which leave little or no 
choice as to where columns can be placed. And even in 
manufacturing plants, the number of bays is generally 
chosen as an odd number in order to provide for a 
center aisle, and this will of course tend to impose 
rather narrow limitations on the column spacing or 
panel size. Very small panel sizes are uneconomical 
The minimum cost will in many cases prevail for panel 


11 


A saw-tooth type of roof of reinforced concrete is su 
Company plant. The beams are braced horizontally 
crete surfaces gives a light and attractive appearance. Designed by A. Epstein. 


sizes approximately 16 ft. in both directions, but eco- 
nomical construction may be obtained for much larger 
dimensions. This phase of the cost problem is often 
affected by rulings and limitations imposed by local 
building codes and by the amount as well as the type 
of live load for which the floor is designed. Practically 
every new site and layout contain different features and 
require individual study. 

After the general outline of the building has been 
studied from the viewpoint of cost, the next step is to 
eliminate all those floor types that are obviously ill 
suited to the requirements. The number of floor designs 
that remains for factory construction seldom exceeds 
three, and typical panels of these, including columns 
and footings, are then designed in order to arrive at 
comparative cost figures. 

There is often an important step left before the pre- 
liminary cost study can be considered complete. Other 
items must be studied and included such as costs of 
sprinkler system, insurance, upkeep and maintenance. 
They may be omitted from the cost analysis only when 
comparison is made between designs of similar char- 
acteristics and identical fire resistance ratings. 

It is frequently difficult to obtain reliable data on 
unit costs for comparative study, and it is therefore 
necessary that the estimator should possess high engi- 
neering ability, wide construction experience, and good 
knowledge of local conditions, 


12 


pported on 50-ft. span continuous girders spaced 20 ft. apart in the Chicago Carton 
by small reinforced concrete struts. The use of form lining and white paint on con- 


5. DIAGONAL ARRANGEMENT 
OF COLUMNS 


A comparison is made in Figs. 14 and 15 between 
two types of column layout for a building that is 66 ft. 
wide between centerlines of exterior columns. Fig. 14 
represents the conventional type of layout, but the lay- 
out in Fig. 15 is sometimes more advantageous. 

In many instances, the production layout requires 
an aisle down the middle of the floor, and the aisle 
seldom needs more than 10 to 12 ft. clear width. The 
column arrangement in Fig. 15 suits this type of layout 
excellently. The columns along the center aisle are not 
only outside the actual working area, but they also serve 
the useful purpose of marking the boundaries of the aisle. 

There is only one row of columns extending through 
each working space in both layouts, but the diagonal 
column arrangement is the more advantageous of the 
two shown. Its longitudinal column spacing (26 ft. 
5 in.) is 20 per cent longer than that in F ig. 14 which 
is only 22 ft., and yet the panel length (18 ft. 8 in.) 
is 15 per cent smaller. This means a considerable reduc- 
tion in cost in the diagonal layout. 

In addition, the load for which interior columns are 
designed is about 40 per cent greater in Fig. 14 than 
in Fig. 15, that is, the diagonal layout requires column 


sizes that are considerably smaller than those in Fig. 
14. Summing up, the diagonal arrangement is seen to 
have certain advantages for layouts requiring a center 
aisle. 

In construction there is but little difference between 
the two layouts. The construction of forms and the 
placing of reinforcing bars are essentially alike in both 
cases if the four-way system of reinforcement is used, 
but the diagonal arrangement works equally well with 
the two-way system of reinforcement. Drop panels, if 


21-6. li-O, 21°C" 
ire ce 


L 220m ator | 220" | 


ONE COLUMN FOR 27.5 x 22= 
605 SQ.FT.OF WORKING SPACE 


Zen O 


Fig. 14. Conventional arrangement of columns. 


any, in Fig. 15 may be constructed with their sides 
parallel to the walls. Figs. 14 and 15 also illustrate 
details of typical framing around large openings, which 
is essentially the same in both layouts. 

In a building with a width, B, the column spacing 


B, Mere 
in Fig. 15 is = in the transverse direction, but the longi- 


5 


tudinal spacing may be made somewhat longer or 
shorter than the transverse spacing. 


Fig. 15. Diagonal arrangement of columns. 


xR 


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x 


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sane 
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COC CCES 
oy 
50505 


POLS 


LS OOD 


Dx 
L 2G-5" [i3t2"| 26:5" | 


ONE COLUMN FOR 27.5 x 26.4 = 
125 SQFT. OF WORKING SPACE 


13 


6. LIVE LOAD, STORY HEIGHT, 
BUILDING WIDTH 


The superimposed load, or live load (L.L.), for which 
a factory floor should be designed deserves careful 
attention. Some designers have used as little as L.L.= 
75 p.s.f., but as a general rule, this low value is not 
satisfactory. By thus limiting the load capacity, a small 
initial saving is effected, but the structure is rendered 
useless for other occupancies with heavier loading. 

The great majority of manufacturing processes can 
be accommodated when the design is made for L.L.= 
150 p.s.f., a loading which is recommended for general 
use. Cost studies indicate that increasing the live load 
from 75 to 150 p.s.f. adds approximately 15 per cent 
to the cost of flat slab construction, including floor, 
columns and footings. The smallness of the cost in- 
crease is well justified by the considerable resale or 
rental value of the heavier design. Structures intended 
for storage may have to be designed for loads higher 
than 150 p.s.f. 

The story height should be adapted to the nature of 
the product and to the needs of the manufacturing 
process, but ceiling heights are seldom less than 12 ft. 
This dimension may be increased to 14 ft. where over- 
head cranes are used and to 16 ft. in order to accom- 
modate mezzanine construction. 

The height from floor to window head, H, has an 
important bearing on the width of the working area, 
W. In Fig. 15, W is the dimension of 26 ft. 5 in. shown 
on either side of the center aisle. Excellent daylight 
illumination will exist over the entire width W, if H= 
0.4 to 0.5 times W. The smaller value of H may be used 
when windows extend the full width between columns 
and when the ceiling has plain surfaces painted white. 
For illustration, consider a building 75 ft. wide between 
centerlines of exterior columns with a layout as in 
Fig. 15. The value of W is 5x==30 {t., ands = 
0.4x30 ft.=12 ft. The story height is then equal to 
12 ft. plus the depth from window head to floor surface, 
which equals about one foot for flat slab construction 
laid out as in Fig. 15. 


7. FLOOR FINISHES 


The floor finish plays an important part in the suc- 
cessful operation of a factory. Basic requirements are 
that an ideal floor finish should be economical, resistant 
to wear, impervious, sanitary, fire resistant, skid-proof, 
inert, and easy to maintain and to keep clean. Con- 
crete is the material used most frequently for floor fin- 
ishes because it can, if constructed according to correct 
specifications, fulfill all these requirements. 

Concrete finish in many factories with constant 
traffic by steel wheeled trucks is subject to more severe 
wear than is concrete in road and bridge slabs. This 
emphasizes the importance of laying concrete floors 


14 


without any stinting on material, or on labor, and in 
strict observance of the rules for good construction 
proved by experience and tests. 

For factory buildings the two-course type of concrete 
floor construction is recommended. The base or struc- 
tural slab is laid first and struck off to a reasonably 
true level not less than 1 in. below the required 
finish grade. Before the concrete has hardened, all 
laitance must be removed by brushing the surface with 
a wire broom so as to leave the coarse aggregate ex- 
posed. This surface is cured for at least 5 days, after 
which the top may be placed whenever convenient. 

Several reasons exist for postponing construction of 
the top course, especially in multi-story buildings. 
Immediately after the structural concrete floor has 
hardened, carpenters may begin placing shores and 
forms for the floor above. The speed of erection that 
can be attained in reinforced concrete construction 
would be impeded if erection of formwork had to wait 
until the wearing surface was placed. If the finish and 
structural base were placed simultaneously, it not only 
would slow down progress on the structural work but 
the finish would seldom get the proper protection and 
curing. The finish can be protected more effectively 
against sun, rain, freezing and unavoidable construc- 
tion damage if it is placed after the structural concrete 
work has been finished and the walls have been built. 

Just prior to placing the top course, the base surface 


is thoroughly cleaned by scrubbing and left soaking 


wet, but all free water must be removed. A thin coat of 
portland cement grout is then broomed into the surface 
a short distance ahead of placing of the top course. 

In placing the top course, exceptional care should be 
given to selection of materials, mixing and placing. 
Fundamental principles of concrete making are the 
same whether applied to floors or to ordinary structural 
uses, but to obtain most successful results, concrete 
finishes for heavy duty must be laid in accordance with 
special, simple rules. A detailed description of these 
rules is given in the booklet entitled Concrete Floor 
Finishes* but the major points will be described briefly. 

The basic requirement is that strong and tough, 
coarse aggregate of suitable wearing qualities (trap 
rock, granite, quartzite) must be distributed uniformly 
throughout a dense, impervious portland cement mor- 
tar. In finishing the surface, operations must be carried 
out so that the coarse aggregate extends clear up to 
the top where it can take the wear from the traffic. 
Under no circumstances should the paste be brought to 
the surface in such amount that it—and not the coarse 
aggregate—is subjected to the wear. This objective is 
essential and is attained largely by the following pro- 
cedure. 

The mixture should be made with approximately 
5 gal. of water for each 94-lb. bag of cement. Moisture 
in the aggregate must be deducted from the 5 gal., the 


*Numerous references on specific related subjects will_be given 
to other publications available free in the United States or Canada 
upon request to Portland Cement Association. 


balance being water to be added. All the aggregate 
should pass the 14-in. sieve. Not more than 5 per cent 
should pass a 100-mesh sieve, and not more than 15 
per cent should pass a 50-mesh sieve. In short, the 
aggregate should be well graded but rather coarse. The 
mix will usually be between the proportions of 1:1:114 
and 1:1:2. This mixture is placed, screeded and com- 
pacted with rollers or tampers. The concrete mixture 
is so dry that many contractors prefer to float it by 
use of power driven floats rather than by handfloating. 
The floating is followed by troweling after all water 
sheen has disappeared. Curing for at least 7 days is an 
essential requirement for concrete made with normal 
portland cement. When high early strength portland 
cement is used, 3 days’ curing is considered adequate. 
If the foregoing rules are followed and the wearing 
course is otherwise placed as outlined in specifications 
in Concrete Floor Finishes, the floor will stand constant 
traffic by hard wheeled trucks without dusting or 
appreciable wear. 

Terrazzo floor finishes are used in entrance halls and 
elsewhere where especially good appearance and pleas- 
ing patterns are desired in addition to the ordinary 
desirable qualities of a concrete floor finish. Specifica- 
tions for terrazzo floors are given in Concrete Floor 
Finishes in which two standard methods of laying the 
floor are fully described. 

Where a special non-slip finish is desired, the floor 


The center aisle in the Chicago Carton Company plant sustains heavy wear from constant trucking. Concrete floor finishes give good 
and enduring service under practically every condition of wear. Note the air-control equipment suspended from the roof which is of 
concrete construction as illustrated in another photograph. 


may be given a “coarse-grained” surface by brooming 
with a hair brush, or non-slip aggregate may be mixed 
with the concrete or sprinkled on the surface just prior 
to compacting. Uniformity of distribution is best ob- 
tained by the former procedure, which requires from 
34 to 1 lb. of non-slip aggregate for each square foot 
of finished surface. The aggregate is exposed by grind- 
ing. Non-slip concrete finishes are used particularly on 
stairways, in front of elevators, or on loading platforms. 
Non-slip surfaces are also highly desirable where floors 
are wet much of the time, such as in creameries and 
slaughter houses. 

In offices, concrete floors may be covered with mate- 
rials such as linoleum, rubber or cork tile. The struc- 
tural concrete is finished to a smooth even surface 
slightly below finish grade. It is essential that the con- 
crete be thoroughly dry before the covering is applied. 
Before laying the covering, place a patch of it on the 
floor and hold it down tight with a weight. If after 
24 hours the concrete looks moist under the patch, it 
is not yet ready for laying the covering. When the con- 
crete is finally dry enough, the covering may be laid 
without danger of “‘blistering’’. 

Linoleum, rubber or cork tile coverings may be used 
also for tool rooms where dropping of hard brittle tools 
on an unyielding surface may cause too much breakage. 
In such places, a wood floor finish may also be used. 
Wood floors in factories are generally of the type in 


15 


Concrete floors are kept neat, clean, and sanitary in the Walgreen 
Company plant, Chicago. They require a minimum of cleaning 


and maintenance. 


which wood is laid in a mastic binder on the top surface 
of the concrete floor. 

Strong acid solutions may require a special acidproof 
covering such as asphalt blocks. The concrete base is 
troweled to a smooth surface and pitched to acid re- 
sistant drains. Premolded blocks may be used and 
pointed with acid resistant compounds, or acid resistant 
mixtures may be laid in place as one continuous sheet. 

With ordinary care and strict adherence to specifica- 
tions for the various types of concrete floors described 
in Concrete Floor Finishes the result is a smooth, im- 
pervious, hard and wear resistant surface which will 
not dust. Faulty construction procedures or use for 
which the floor was not intended when placed may 
combine to expose flaws here and there on the surface. 
Such flaws should be repaired just as soon as possible. 
It is poor economy to delay repairs because the steady 
pounding of truck wheels over a weak spot will gradu- 


ally break down adjacent concrete which is in sound 
condition. The repair procedure is to chip away the 
damaged concrete to a depth of at least 1 in. and to 
put in a patch. The depth of the patch must be uniform. 
and no feathered edges should be permitted because 
they may break down rapidly. The hole must have 
vertical edges as illustrated in Fig. 16. 

The patch must not be struck off flush with the top 
of the surrounding floor because then the patch will 
ultimately harden as a depressed area. The correct 
procedure is to run the strike-off board on shims laid 
on the old concrete around the patch, leaving the new 
concrete surface slightly above the old surface as illus- 
trated in Fig. 17. After one to two hours, the patch is 
troweled down to its final grade, flush with the rest of 
the floor. 

It is important that the patching concrete be as 
nearly as possible of the same mix as the original finish 
and that it be cured thoroughly as required for a heavy 
duty floor finish. Protection of the patch during curing 
may be insured by covering the area with a boiler plate 
with its convex side upward. 

In addition to occasional patching, the only other 
maintenance, but an important one, is the cleaning 
of the floor surface. Accumulations of grit, nails, oil, 
dirt, molasses and sugar are detrimental to safety of 


_ the workers and may cause damage to the finish. Warm 


soapy water and stiff brushes will remove ordinary 
accumulations. After scrubbing, the floor should be 
mopped dry. Special cleaning methods for soiled floors 
are discussed in Concrete Floor Finishes. 

In truck yards where a concrete slab is laid direct 
on the subsoil, a one-course construction is used. The 
construction is similar to that of highway concrete 
slabs, a rough broomed finish is used, and joints divide 
the slab into squares or rectangles.* 

If the truck yard is over a basement or other occupied 
space, flat slab and two-way solid slab constructions 
are well suited for support of the loading. Design and 
detailing of joints are similar to corresponding features 
in bridges. The surface should be sloped to drain inlets 
and expansion joints should be installed as illustrated 
in Fig. 18.** Drainage gutters of sheet metal under 
expansion joints are recommended if leakage through 
joints will spoil contents stored below the yard floor. 
Downspouts should be exposed so that they can be 
cleaned out or replaced. 


*See booklet Concrele Pavement Design. 
**Further description and additional details are given in 
booklet entitled Conerete Bridge Details. 


STRIKE - OFF BOARD 


CORRECT 


INCORRECT 


Fig. 16. Floor patch, correct and incorrect chipping. 


16 


CORRECT INCORRECT 


Fig. 17. Floor patch, correct and incorrect strike-off. 


“—=TAP SCREWS 


BED AO O D p en Q: 


LLL 


LLL. 


STRAP ANCHORS 


Fig. 18. Expansion joint detail for truck yards. 


8. STAIRS 


Study of fires in factories reveals that rather heavy 
loss of life is due to poor layout and inadequate main- 
tenance of the exits combined with inferior construction. 
A fire or an explosion is apt to cause panic which in 
turn may lead to injury or death, especially at inade- 
quate stairways and exits. 

The problem of stairway design has been subject to 
thorough investigation the results of which, together 
with definite design standards, have been made avail- 
able in print. For important sources of information 
reference is made to the U. S. Department of Commerce 
bulletin entitled Design and Construction of Building 
Exzits,* and to Building Exits Code, published by the 
National Fire Protection Association.** 

Stairways are measured in units of 22-in. width, each 
of which accommodates one person. A width of two 
units, 44 in., is considered minimum for factory stairs 
although a sub-standard width of 36 in. is accepted for 
certain limited instances. A 44-in. or a 66-in. stairway 
should have handrails on both sides. For larger width, 
the addition of a center handrail is recommended. 
Handrails projecting not more than 3% in. are not 
considered as encroaching upon the useful width but 
beams, columns and other obstructions are not per- 
mitted within the minimum widths. 

The uninterrupted vertical height of a flight of stairs 
is limited to 12 ft. or, in some instances, even to 8 ft. 
Two flights with one intermediate landing is standard 
construction in factories. It is not permitted to use 
winders or to use flights having less than three steps 
each. 

Fire doors at entrances to stairways must open 
toward the stairs. If doors can be folded back against 
the wall, they are not considered an obstruction in 
the stairway, but at any point of the swing the door 
must leave not less than 36 in. of the stairway unob- 
structed. 


The usual rules for the dimensions of risers and 
treads, the latter being measured horizontally from 
nosing to nosing, are: 


(1) Sum of one tread and two risers to be not less 
than 24 in. nor more than 25 in.; 

(2) No riser to exceed 734 in.; 

(3) No tread to be less than 9 in.t 


Stairs designed accordingly have been found ade- 
quate, safe and practical. People are used to such steps 
and therefore can use them with the greatest degree of 
convenience. 

There should be at least two 44-in. stairways in every 
factory building (except under certain sub-standard 
conditions), but more than two stairs may be required. 
Problems concerning number of stairways have been 
given exhaustive study, from which certain rules have 
been developed. 

One rule concerns the distance any occupant on a 
floor has to travel to reach a stairway. One hundred 
feet is generally considered maximum length of travel 
in buildings in the classification known as “high hazard 
occupancy”.t The distance permitted is 150 ft. in 
buildings that are equipped with sprinklers and built 
of fire resistant construction. 

Other rules concern the time in which the building 
can be evacuated, counting 45 persons per unit width 
in one minute walking down the stairs. Or the basis 
for calculating the number of stair units may be the 
requirement that all occupants should be able to find 
refuge on the stairs, one person being assumed to occupy 
every other tread with a corresponding number of 
persons on the landings. 

One simple rule has been formulated as follows: 
Units of exit width shall be provided for each story 
above the first by dividing gross area of floor in one 
story (in square feet) by 6,000 for low or medium haz- 
ard occupancy or by 3,000 for high hazard occupancy. 

Non-enclosed stairs of the type known as fire escapes 
are not to be counted as regular stairways. The enclosed 
fire escapes or smokeproof stair towers used in certain 
territories differ from interior stairs mainly in that 
glazing is omitted in the window apertures. Smokeproof 
stair towers as well as interior stairs should be pro- 
tected against infiltration of smoke by means of a 
vestibule at the entrance to the stairs. The vestibule 
must be isolated by self-closing fire doors and must 
not open directly on the stair treads but should open 
on a landing. Doors must swing in the direction of travel 
to the outside. 

If the stairs do not open direct to the outside at 
ground level, a protected passageway must be provided 


*Available from Superintendent of Documents, Washington, 
D.C. 

**A ddress: 60 Batterymarch Street, Boston, Mass. 

+Other rules in use are: sum of riser and tread to be 1714 to 
18 in.; product of riser and tread to be 70 to 75. 


tFor definition of occupancy rated as “high, medium, and 
low hazard’, see Building Exits Code referred to in this section. 


17 


CEILING LINE gi 


for connection to outside. 

Boiler rooms and other 
rooms below street level 
must have two exits, one of 
which may be a ladder lead- 
ing direct to the street. 

The question of enclosure 
for stairways is an import- 
ant one. There should be no 
Openings in the enclosure 
except those needed for 
access and light. The enclos- 
ing walls as well as the stair 
structure itself should be of 
incombustible material and 
should have at least a 2- 
hour fire rating. The U. S. 
Department of Commerce 
bulletin on Fire Resistance 
Requirements* gives a 2-hour 
rating to walls of (1) 4-in. 
concrete block, plastered on 
both sides**, and to (2) 4-in. 
solid concrete with not less 
than 0.2 per cent reinforce- 
ment in each direction. 
When plastered on both 
sides, a 3-in. thickness of 
concrete is sufficient. 

For the determination of 
headroom required in stair- 


18 


REFERENCE LINE na 


: RAILING LINE 

ye a wo 

} ‘ wae | 
; | 


= 


yl a 


ways, the procedure illustrated in Fig. 19 is quite com- 
monly used. Mark a reference line parallel with the 
steps at a height measured vertically 4 ft. 6 in. above 
the line through the stair nosings. A clearance of 2 ft. 
6 in. as shown with respect to the reference line is con- 
sidered the minimum allowed. Determination of the 
height at which the railing is to be attached is also 
illustrated in Fig. 19. 

The framing in a floor slab for a stair opening may 
be made in accordance with the types of framing which 
are illustrated for openings in Figs. 10 and 11. Fig. 20 
shows a typical vertical section through a stairway 
suitable for an industrial building. The inclined con- 
crete stair slab is designed as a one-way slab supported 
on and cast integrally with beams as shown. The land- 
ing construction may be suspended by hangers from 
the floor above, supported on concrete struts from the 
floor below, or may bear on the enclosing walls. A live 
load of 100 p.s.f. is satisfactory for stair design. Rein- 
forcing bars extending from the inclined slab into the 
landing slabs should not be bent at re-entrant angles 
but should be lapped as indicated. 


*See reference in Section 11. 


**The block thickness and requirements for plaster depend 
upon the type of aggregate used and the face shell thickness. 


ZZ, 


1O TREADS @ JI"= 9:2" 
ZA vé ae TEMES 

LE pees | ge : 
Sage (sees un 
iver B 9 
Ge - 
en ee )) 
a eA TA 
ZA ow 
> RSOLIDESEAG a 
A°>-G"O.C. ALT. BARS BENT 5 
TRANS.BARS ZEPER TREAD © 


LE 
eg we 


i048 


7 


HW RISERS @ 1"2@ 


Fig. 20. Vertical section through concrete stairs. 


Two types of stair slab finishes are illustrated in 
Figs. 21 and 22. In both of them, the structural stair 
slab is cast first as outlined. Later on, the finish is 
applied either as a regular two-course construction, 
see Fig. 21, or the finish may be of precast units as in 
Fig. 22. Both types give excellent service and are often 
built with a non-slip surface. 

It is good practice to place stairways in separate 


Fig. 21. Two-course cast-in-place concrete finish on stairs, 


Foundry building at Garfield, Utah, has rigid frame concrete roof with 70-ft. span. Mezzanine construction and crane rail brackets are cast 
integrally with columns. Ample daylight is provided through tall windows and monitors. Designed and constructed by Villadsen Bros., Inc. 


tower structures adjacent to the factory building. In 
addition, such towers are sometimes used to house 
elevators and utilities including risers for electricity, 
steam, water and compressed air. The top of the tower 
accommodates elevator machinery and water tank. 
The use of utility towers has the advantage that the 
entire width and length of the floors are left unob- 
structed. 


eae 


MCONGRET ENT: 
° ° e ee . mor 


70/7 REINFORCED C 


Fig. 22. Precast concrete finish on stairs, 


19 


9. WALLS 


A characteristic feature in factory walls is that piers 
between windows are reduced to the least possible 
number and width. As a rule, the pier width is made 
not greater than the width required for the support of 
loads, and the main function of the pier is therefore a 
structural one. Since factory design architecturally may 
be said to be ‘‘functional”, the tendency is naturally 
to expose the structural material in the wall. Concrete 
is both a structural and an architectural medium, and 
this double function makes concrete particularly well 
suited for wall construction in factories. 

“Architectural concrete’ exposed in the walls differs 
from ‘‘structural concrete” mainly in that special care 
must be taken to make forms for architectural concrete 
substantial, true and tight. They must also be so de- 
signed that they can be stripped without danger of 
damaging corners and lines. Various designs involving 
recesses and offsets may be used, and many attractive 


Io 


MASTIG 
CAULKIN 


METAL CLIP 
SET INCONCRETE 


ROWELED 
SURFACE 
Are 
7 gE’? TIE 
2 "> BARS 


le -TCONSTRUCTION 
1 JOINT 


MIN.I" 


Supe. 


Fig. 23. Steel sash set in concrete wall. 


20 


textures and details may be obtained by judicious use 
of form lumber, linings and waste molds.* 


Windows in factories are generally of steel sash, and 
the best practice is to set them after the forms have 
been stripped. Fig. 23 shows details of steel sash set in 
a concrete wall. It illustrates how rabbets and reveals 
are provided to receive the window frame. The window 
sill in Fig. 23 is of the projecting type, but window sills 
may also be made flush with the spandrel.** Special 
attention should be given to setting the window frame 
so that it is perfectly tight, but no part of the window 
frame should be embedded in the wall concrete because 
corrosion of the steel may then damage the surround- 
ing concrete. 


Spandrels serve as structural members and also as 
important elements in the architectural design. Both 
requirements are fulfilled with architectural concrete 
construction. Spandrels may extend both above the 
floor and below the ceiling, but in best factory design 
spandrels do not project below the ceiling. If the struc- 
tural requirements of a spandrel can be met with a 
depth equal to the depth of the floor itself, a construc- 
tion joint may be placed at floor level. This simplifies 
the construction of forms and the placing of concrete. 
If necessary, the construction joint may be concealed 
by means of a groove, an offset or other architectural 
detail. 

It may be necessary to include in the spandrel beam 
the entire depth from window head below to window 
sill above. An upturned spandrel should usually be con- 
creted in one continuous operation simultaneous with 
the adjacent floor. In this case, construction joints are 
placed at window heads and at window aills.t 


Expansion joints may be used in long buildings and 
must be used where a new building unit is attached to 
one previously constructed. Observations indicate that 
buildings of architectural concrete seldom need expan- 
sion joints, unless they are more than 200 ft. long. 
Additional joints may be necessary in buildings with 
wings, offsets or other irregular shape. 

The function of expansion joints in factory buildings 
generally is to allow for shrinkage and temperature 
change. In warm weather construction, the space in 
the joint should be not more than 1% in., but a some- 
what larger space may be needed in cold weather con- 
struction. The clear distance of 1 in. shown in Fig. 24 
is assumed to represent the joint at its widest position. 
The flexible copper strip near the exposed face of the 
wall keeps out water and air. One detail in Fig. 24 
shows a joint in a wall without offset. The joint in the 


*Important details are described in booklet Forms for Archi- 
tectural Concrete and in concrete information sheet, Teztures. 

**Details for both types are given in Windows, which contains 
numerous details for forms, plastered walls, wood sash, reinforce- 
ment and cased openings. 

{Details for several types of spandrel forms and for reinforce- 
ment are presented in Spandrels. Architectural concrete walls 
embrace many other details besides those discussed. For sketches, 
photographs and description of such details, reference is made to 
concrete information sheets Doorways; Reveals; Pilasters; Orna- 
ment; Canopies; Control Joints. 


OUTSI DES ——. 


2x G’ BRASS OR BRONZE ex4' STEEL 
PLATE - TAP SCREWED TO PLATE 


2"xI" BRASS OR 
BRONZE PLATE 


BED PLATE - SCREWS G"OC. 


METAL LATH 
BENT AROUND ANGLE 
METAL TRIM 


TAP SCREWED) \ SLIDING SURFACE 
TO JAMB 


Fig. 24. Expansion joints for concrete walls. 


other detail is partly concealed by means of an offset. 
The detail showing a partition at the joint is suitable 
where a new unit is added to a present building, but 
otherwise it is better to avoid having partitions at 


~ 12"TO 16" 0.C. HORIZ. 
i 2.104 ©1E. VERT 
nae) 


os 


° . 

ae . = Co S00 : 3 . 
Sy ee rata ° ene) . a toile oe os ‘ 
ao raha Cap a eS ee OM ae O Se he . 


#12 GALVANIZED WIRE LOOPS SET IN 
JOINTS BETWEEN FORM BOARDS 


No ae | 
I: ren? : WEDGED FOR ALIGNMENT fue oo 
pla Oe Oe Gh ie eed 


PLACE AND WEDGED FOR ALIG 
MASONRY FURRING MAY ALSC 
BY THIS METHOD 


Fig. 25. Furring for architectural concrete walls. 


GZ 
m 


joints. Expansion joints should be carried through 
basement walls and, of course, also through parapets.* 
Control joints should be provided in the walls at inter- 
vals of 20 to 25 ft. Such joints are generally located at 
the jambs or centerlines of openings. 


Thermal insulation of walls is not, as a rule, required 
in factories. In air conditioned plants, however, the 
concrete walls may have to be insulated, and insulation 
becomes a necessity in cold storage warehouses. Fig. 25 
illustrates two stages of the construction of a wall that 
is to be furred with insulation board. Galvanized wire 
loops are indicated as the means of attaching furring 
strips to the wall.** 


Reinforcement in architectural concrete walls should 
be designed and detailed to resist stresses created by 
gravity and exterior forces. In addition, adequate rein- 
forcement must be provided for stresses caused by 
volume changes in accordance with the recommenda- 
tions in the table in this section. Note that all bars in 
the table are 3% in. round, with spacings from 6 to 
12 in. Larger bars with greater spacings are less effec- 
tive in preventing cracking. Additional bars are placed 
at openings as illustrated in Fig. 26. Vertical bars in 
spandrels should preferably be detailed as U-stirrups. 
The arrangement of typical wall reinforcement is shown 


*Full description of various joint details in walls, floors and 
roofs is given in Hxpansion Joints in Concrete Buildings. 

**Other means of attachment are shown in detail together 
with a discussion of thermal insulation in Furring for Architec- 
tural Concrete Walls. 


MIN.2-3"® BARS 
OVER ALL OPENINGS 


FOR G"ORS8"WALLS 
USE 1-2" BAR 


FOR 10" OR I2"WALLS 
USE 2-3"> BARS 


Fig. 26. Reinforcement around wall openings. 


Fy yr wre 6 


Spinning mill at Bridgeport, Pennsylvania, designed by The Ballinger Company, has flat slab floor cantilevered beyond the exterior 
columns, and windows are made continuous around the building. Lighting is further improved by giving concrete surfaces a coat of 
white semi-gloss paint. Note the pipe holes for future use at each column head and the inserts in ceiling for suspension of pipes. 


in Fig. 27. There is only one curtain of bars in the 6 
and 8-in. walls, but two curtains in thicker walls. In 
the outside curtain, the vertical bars are placed at a 
clear distance of 2 in. from the outside face, and the 
horizontal bars are tied to the inside of the vertical 
bars. This arrangement permits puddling concrete be- 
tween the outside forms and the reinforcement and 
leaves ample room to use an elephant trunk or spout 
for placing concrete. Bar splices should have a 30- 
diameter lap for 3,000-lb. concrete and a 40-diameter 


WALL REINFORCEMENT 


Wall 
Thickness 
Inches 


Horizontal 
Reinforcement 


Vertical 
Reinforcement 


6 


10 


34-in. round at 8-in. 
centers in outside 
face of wall. 

3%-in. round at 6-in. 
centers in outside 
face of wall. 

34-in. round at 10-in. 
centers in both 
faces of wall. 

34-in. round at 8-in. 
centers in both 
faces of wall. 


34-in. round at 8-in. 
centers in outside 
face of wall. 

3%-in. round at 8-in. 
centers in outside 
face of wall. 

34-in. round at 12-in. 
centers in both 
faces of wall. 

34-in. round at 12-in. 
centers in both 
faces of wall. 


lap for 2,500-lb. concrete.* 

Means of moving boilers and other large equipment 
in and out of the building should be considered and 
suitable openings provided in both floors and walls. 
Window openings are usually sufficiently large for this 
purpose, but if not, they may be enlarged by means of 
removable concrete panels. 


*For further details and discussion, reference is made to 
Reinforcement for Architectural Concrete Walls. 


OUTSIDE FACE Fe "MIN. 
OF WALL ny on 


6&8" WALL lO"G& 12" WALL 


Fig. 27. Location of reinforcement in concrete walls. 


10. ROOFS 


The superimposed loads on roofs required in various 
codes vary from 25 to 50 p.s.f., and to this load must be 
added from 5 to 8 p.s.f. for ordinary roofing, plus 5 p.s.f. 
for insulation board, if required. 

No slope need be provided for drainage of flat roofs; 
in fact, it is preferable to make them absolutely level. 
Drains and overflows are frequently placed at least 
2 in. above roof level. As a result, a sheet of water 
covers the roof practically all the time. This helps to 
preserve the roofing and also by slow evaporation 
assists materially in cooling the story below the roof. 

At all vertical surfaces roofing should be flashed and 
counter flashed as illustrated in Fig. 28. When the 


PARAPET OR COPING 


RAGGLE 
CALIKING 


COUNTER 
FLASHING 


FLASHING 
ROOFING 


INSULATION 


Boe: 
WALL 
Fig. 28. Roofing and flashing at parapet. 

parapet is cast, a raggle is provided as shown, and the 
flashing is later calked securely in this groove. The 
height from roof to raggle depends upon climate and 
precipitation. A detail similar to that in Fig. 28 is 
used around openings for skylights.* 

In places where parapets are not required, the roofing 
and flashing detail in Fig. 29 may be used. A continu- 
ous wood blocking is set in and fastened to the concrete 


ROOFING 


FLASHING INSULATION 


WALL 
Fig. 29. Flashing and gutter for roof without parapet. 


NAILING BLOCKS 


FLASHING SOLDER HEAD NAIL 


\ 


Ape) ey et 


sed Pee obr Oh aes: 
<= lI" EXPANSION JOINT 


Fig. 30. Expansion joint in roof. 


when it is cast, and both flashing and gutter are later 
attached to the blocking. 

Expansion joints in roofs may be constructed as 
shown in Fig. 30. It is essential that the joints be both 
watertight and flexible. On either side of the joint a 
parapet is built which is similar to that illustrated in 
Fig. 28. The tops of the two parapets are covered with 
a flashing which is nailed to a block on one side of the 
joint but not fastened to the other side.** 

For both flat and pitched roofs, a concrete joist 
floor design is suitable. If the supporting structure is 
of concrete, it is cast integrally with the decking. If 
steel roof trusses are used, all forms for the decking 
may be attached to and supported by the roof structure. 

A type of roof deck frequently used consists of con- 
crete made wilh stone, gravel, slag or special light- 
weight aggregates, which is cast on metal lath or on 
wire mesh with paper backup. The lath or mesh is 
supported and stretched on purlins. This type of slab 
when covered with insulation and roofing gives excellent 
service at low cost. The lath provides a good ground 
for plastering, or the bottom of the roof construction 
may be concealed and protected against fire by a sus- 
pended ceiling consisting of cement plaster on metal 
lath supported by pencil rods hanging from the roof. 

Insulated roof decks may be constructed by placing 
the concrete on cork slabs, the contact surfaces of 
which are so prepared that they bond with the bottom 
of the concrete slab without mechanical aid, although 
wire loops are sometimes hooked into the cork to in- 
sure positive anchorage. Such cork slabs serve simul- 
taneously as the form for the concrete, as insulation, 
and as acoustic lining for the ceiling. Other properly 
prepared insulating boards may be used in lieu of cork. 

For long-span roofs, several types of rigid frames of 
reinforced concrete and also reinforced concrete shell 
structures are available. The top member of the rigid 
frame may be straight from parapet to parapet, or it 


*Copings for architectural concrete walls may be either pre- 
cast or cast-in-place. Both details, together with reinforcement 
and forms, are illustrated in Copings and Parapels. 

**Another detail and full description are given in Expansion 
Joints in Concrete Buildings. 


23 


Barrel shell roof of reinforced concrete with average shell thickness of 3/4 in. used in factory building with 188,000 sq.ft. of usable floor 
area occupied by Armstrong Tire and Rubber Company, Natchez, Miss. This building, which is of concrete throughout, has the lowest 
possible cost of maintenance and fire insurance, The bays are 40 ft. wide and the typical longitudinal spacing of columns is 50 ft. Designed 


by Roberts and Schaefer Co., Chicago. 


may be pitched as shown in Fig. 31.* Rigid frames of 
similar shape may be built continuous over two or more 
spans. The decking or roof slab spanning from frame 


MONITOR 


PARAPET 


WINDOW 


CONC.RIGID FRAME 
WINDOW 


(7 Mit EMBEDDED IN CONC. FLOOR 


to frame may be either a solid slab on concrete beams, 
or a ribbed slab may be used. 


There are two basic types of reinforced concrete 


*The analysis of building frames of the types in Fig. 31 is 
illustrated by many numerical problems presented in One-Story 
Concrete Frames Analyzed by Moment Distribution, and Gabled 
Concrete Roofs Analyzed by Moment Distribution. 


CONC. DIAPHRAGMS 
AT COLUMNS 


XY CONC. SHELL 


Fig. 32. Butterfly type concrete shell roof for spans up to 
40x60 ft. 


shell roofs* especially adapted to industrial buildings. 
They are: (1) the butterfly type for spans up to 40x 
60 ft. (see Fig. 32); and (2) the barrel shell type for 
spans up to 60x200 ft. (see Fig. 33). In such roofs the 
shell, which usually has a thickness of 3 or 314 in., is 
stiffened by edge members and diaphragms. The curved 
and stiffened shells have ample strength to carry any 
loads to which they are subjected, including unbalanced 
wind and snow loads, with a large factor of safety in 
spite of the very long spans for which they are used. 

The total absence of interior columns in many cases 
and the wide spacing of columns where they are re- 
quired at all is a distinct advantage of shell roof con- 
struction for industrial plants. In buildings that are 
too wide to be illuminated adequately from side-wall 
sash, skylights can be provided in either the barrel 
shell or butterfly type roofs, so a good distribution of 
light may be had in even the widest buildings. 

Concrete used on the slope of a pitched roof or on 
the steeply pitched portion of a shell roof should be 
placed fairly stiff. If the correct consistency is used, 
top forms are not needed for slopes less than approxi- 
mately 45 degrees. The concrete finishers may do their 
work from scaffolds supported by wooden shoes on the 
freshly placed concrete. On slopes steeper than approxi- 
mately 45 degrees, concrete of stiff consistency is first 
placed and then covered with a top form as the work 
progresses. 

On pitched roofs shingles of various types, including 
those made of asbestos fiber and portland cement, are 
sometimes used. They can be nailed directly to the 
roof slab. Special case-hardened nails are available on 
the market for nailing into precast concrete slabs or 
fills made of nailable concrete, which may be of the 
aerated type, or may be made of lightweight aggregate. 

Corrugated sheets made of asbestos fibre and port- 
land cement are used extensively on steep slopes. On 
flat surfaces, the corrugated cement-asbestos sheets 
may be used if covered with a lightweight fill and roof- 
ing membrane. This roof type requires no formwork, 
and the fill serves both as base for the roofing and as 
insulating material. 


“EDGE BEAMS ~~ CONC. DIAPHRAGMS 
AT COLUMNS 


Fig. 33. Barrel type concrete shell roof for spans up to 
60x200 ft. 


Construction view of concrete roof structure of Armour and Com- 

pany beef house. Attention is called to the arrangement and plac- 

ing of reinforcement, to formwork details, to inserts and collars 
for openings in floors. 


Various types of precast concrete construction have 
been used for roofs. They require little or no formwork, 
are economical for supporting relatively light super- 
imposed load, and are easy to handle and place. 

The precast concrete joists illustrated in Fig. 34 are 
available with over-all depths of 8,10, and 12 in., and 
may be used on spans up to 24 ft. The joists are set 
on the supports, and wood forms attached to them for 
a concrete topping slab, 2 or 21% in. thick. The joists 
extend 14 in. into the cast-in-place slab and are doweled 
to it. Insulation board, if any, and roofing membrane 


*See “Principles of Concrete Shell Dome Design,” by Eric C. 
Molke and J. E. Kalinka, Journal of the American Concrete 
Institute, May-June, 1938. 


CAST-IN-PLACE SLAB 


Herre Te) Soe Se a5 age 
si Or ONEISOn eee. IS eataaues 


Fig. 34. Precast concrete joist roof construction. 


Construction view of addition to A. B. Dick Building, Chicago, 

designed by Nimmons, Carr and Wright, architects, illustrates 

numerous steps in connection with the simple erection of forms 

for flat slab. The first step is shown in the lower portion and the 

last step in the upper portion of the photograph. Built by B-W 
Construction Company. 


are placed on top of the slab.* 

Concrete tile of various types are used frequently 
on roofs and give an excellent, economical construc- 
tion. In general, the tile are 2 ft. wide and are laid on 
purlins spaced up to 8 ft. apart. Some tile are flat on 
both top and bottom, but others, called channel tile, 
consist of a slab with thickened edges on the two longer 
sides. Lightweight concrete is generally used to facili- 
tate handling, and numerous special shapes are manu- 
factured for connections, eaves, ridges, valleys, and for 
other special requirements. A nailing concrete is some- 
times cast integrally on top of the tile for fastening of 
ornamental roofings, but ordinary membrane roofing 
laid in mastic directly on top of tile requires no nailing. 


26 


I]. FIRE RESISTANCE 
REQUIREMENTS 


Standards have been adopted by which fire resist- 
ance qualities of types of construction are specified and 
evaluated. It is not sufficient merely to distinguish 
between ‘‘fireproof’ and “‘non-fireproof” construction. 
The designer now describes a structure or a part thereof 
by saying that it has a fire resistance of a certain dura- 
tion, or differently expressed, that it can withstand 
exposure to fire for a certain number of hours. 

The Building Code Committee of the Department 
of Commerce in 1931 made a report entitled Recom- 
mended Minimum Requirements for Fire Resistance in 
Buildings.** The committee specified the fire resistance 
required for important structural parts in buildings of 
various types of construction. Some of the committee’s 
requirements given in terms of hours are listed in the 
table below. The committee also established fire re- 
sistance ratings in hours for various structural parts. 

The two types of construction included in the table 
do not have equal fire resistance. Type 1, described as 
“fully protected”’, has a fire resistance which is superior 
to that of Type 2, called ‘“‘protected’’ construction. 
Type 2 may cost less to build but it is subject to higher 


FIRE RESISTANCE REQUIREMENTS IN HOURS 


Type of Construction! 


Structural Part 1. Fully Protected 2. Protected 
Walls—Fire 4 4 
Party 4 4 
Bearing 4 3 
Others 2% 2, 
Piers 4 3 
Columns—Supporting walls 4 3 
Others 4 2 
Girders—Supporting walls 4 3 
Others 2% 2s 
Trusses—Supporting walls 4 3" 
Others 4 1% 
Beams 2% 1% 
Floors 2% 1% 
Roofs 2% 1% 


‘For other types, see Recommended Minimum Requirements 


for Fire Resistance in Buildings. 


insurance rates and more stringent restrictions are 
applied to its use than to Type 1. 

The use of the table may be illustrated by consider- 
ing a simple example. In fully protected construction 
all columns shall have a fire resistance of 4 hours. The 
designer may use any one of several available types of 
columns, provided they have a 4-hour rating. 

The committee report also includes ratings for vari- 
ous structural parts with numerous types of fire pro- 


*Numerous details and loading tables are presented in the 
booklet Precast Concrete Joists in Floor and Roof Construction. 

**Available from Superintendent of Documents, Washington, 
D. C. This report is being used as the basis for fire resistance 
ordinances in numerous municipalities. 


tection. The 4-hour rating required for columns is 
satisfied by use of “Reinforced concrete, coarse aggre- 
gate ‘A’,** 114-in. concrete protection outside the bars’. 
The 2)4-hr. rating required for beams is satisfied by 
use of “Reinforced concrete, any type of coarse aggre- 
gate, 114-in. concrete protection’. The 2)4-hr. rating 
for floors and roofs is satisfied by use of several types 
of construction, one of which is ‘‘Reinforced concrete 
solid slab, minimum thickness of 41% in., 34-in. con- 
crete protection below bars’. The 4-hr. rating required 
for walls is satisfied by use of ‘Reinforced concrete, 
6-in. minimum thickness, 0.2 per cent reinforcement in 
each direction’. 

The fully protected type of construction discussed is, 
from the standpoint of fire, not restricted in respect to 
occupancy, height of building, or size of floor area. 
Certain restrictions are applied, however, to other in- 
ferior types of construction. The “‘protected” type of 
construction, for example, is limited to a building height 
of 50 ft. for garages and 80 ft. for factories and ware- 
houses. The total floor area is limited to 25,000 sq. ft. 

The purpose of providing fire resistance in floors and 
walls would be defeated if vertical shafts for stairways, 
elevators and other purposes were not given proper 
attention. Recommendations for shaft enclosures and 
for protection of openings in walls are included in the 
committee’s report which requires shaft enclosures 
having a 2-hour rating and approved doors. 

Fire laws and ordinances for congested areas favor or 
even demand the best type of fire resistant construction 
because a fire hazard in any building is a constant 
threat to adjacent property. On the other hand, less fire 
resistant construction is often permitted in outlying or 
suburban areas where there is less congestion. Higher 
insurance premiums on such construction and possible 
business loss due to shut-down in case of fire will often 
offset any saving in first cost and make the use of the 
best type of fire resistant construction advisable. 


12. DESIGN FOR ADDITIONAL 
STORIES 


It is good practice to plan a building in its final ex- 
panded shape even if it is intended to build that portion 
only which is required for present needs. In doing this, 
the designer will invariably give thought to various 
details which might otherwise be overlooked. 

Provision should be made in the original design for 
adding new stories to the building by making footings 
and columns of sufficient size to carry future loads. If 
this is done, no structural change is involved when 
expansion becomes necessary. 

The case may come up in which it is desired to add 
more floors than originally planned, a case which may 
be handled in one of several ways. It is possible that 
some of the floors will not be loaded as heavily as 
assumed in the original design. Lower load limits may 
then be established and advantage can be taken of the 


load reduction. It is also possible that changes have 
been made in the building code which permit an in- 
creased load on columns already built. 


In most cases, however, it will become necessary to 
consider the use of dead loads for new construction 
which are smaller than those anticipated in the original 
design. This may be done by choosing the type of con- 
crete floor design which requires the least volume of 
concrete, by specifying a lightweight concrete, or by a 
combination of both. 


The concrete joist floor system with removable metal 
pans is one of the lightest types suitable for manufac- 
turing buildings. In the one-way concrete joist floor, 
the metal pans are generally 20 or 30 in. wide separated 
by joists not less than 5 in. wide. The pans may have 
tapered ends in order to provide for shear and com- 
pression stresses at supports. The general layout of a 
concrete joist floor is illustrated for garages in Section 
22. In factory floors, a bridging joist, say 5 in. wide, 
should be added at midspan running perpendicular to 
the main joists in order to help distribute heavy con- 
centrated loads. 


Lightweight concrete may be designed with a weight 
of approximately 100 lb. per cu. ft. Its use will account 
for a reduction of approximately one-third in the dead 
load as compared with ordinary stone or gravel con- 
crete. Several types of lightweight concrete aggregates 
are available. ft 


An important point in connection with design of tall 
buildings is the reductions allowed in live loads used 
for design of columns and footings. A building code 
committee appointed by the U. 8. Department of Com- 
merce submitted in 1924 a report on “Minimum Live 
Loads Allowable for Use in Design of Buildings’’.t The 
committee reported on “‘Reductions in Live Loads’’as 
follows: “‘Except in buildings for storage purposes, the 
following reductions . . . are permissible in designing all 
columns, piers or walls, foundations, trusses and girders. 

‘Reduction of total live loads carried: 


Member Per Cent Member Per Cent 
Carrying Reduction Carrying Reduction 
one floor....... 0 five floors...... 40 
two floors...... 10 six floors...... 45 
three floors. ... 20 seven or more 
four floors. .... 30 floors....... 50” 


A footing is designed for the load used for design of 
the column immediately above the footing. These 
reductions in live loads recommended by the committee 
are greater than those given in most old municipal 
codes. They are recommended for use both in new 
designs and in investigations of present columns and 
footings for their ability to support additional floors. 


**Limestone, calcareous gravel, trap rock, blast furnace slag, 
burnt clay or burnt shale. 


{For detailed discussion of one of them, reference is made to 
Haydite Concrete. 


tAvailable from Superintendent of Documents, Government 
Printing Office, Washington, D.C. 


27 


Continuous gabled frames of reinforced concrete support concrete roof slab in the International Amphitheater, Union Stockyards, Chicago. 


The structure is intended for exhibitions, but the type is equally well suited for manufacturing. Designed by Al Epstein. 


13. DETAILS FOR ADDITIONAL 
STORIES 


A most important detail in connection with adding 
new stories to an old concrete structure concerns dowel- 
ing of vertical column bars. It has been customary to 
provide dowels projecting at least 24 diameters above 
the present roof level. In order to protect the dowels 
against corrosion, they have been greased or painted 
and covered with either a wooden box or a block of cast- 
in-place lean concrete, later to be chipped away. 

The drawback in using the dowel detail was that the 
dowels pierced the membranes provided for insulation 
and waterproofing. To avoid this defect, some engineers 
omitted dowels, stopped vertical bars a short distance 
below top of concrete roof level, and placed pipe sleeves 
around the top of the bars. It has been found difficult, 
however, to locate and clean out such pipe sleeves be- 
fore making them ready for extension of the columns. 
Another objection is that the butt joint is not con- 
sidered adequate for transmittal of stress from bar 
above to bar below. 

Welding may be used advantageously for fastening 
future to present column bars. Top story column bars 


28 


may be extended 2 to 3 in. above present concrete roof 
level and covered with a fill which is just thick enough 
to conceal the top of the bars. The roofing membranes 
are laid on the fill. When new stories are to be added, 
remove roofing and fill, and weld new bars to the old 
bar stubs. Certain lightweight concretes with rela- 
tively high insulation value are particularly suited for 
fill. The fill will be easier to remove if laid on building 
paper, and it should be reinforced in both directions in 
order to minimize any tendency it may have to “creep” 
on the roof slab. 

Parapets in buildings of architectural concrete should 
be detailed so that they may readily be incorporated as 
part of the future wall to be erected above. Brick para- 
pets in buildings with wall columns must be wholly or 
in part reconstructed when columns are extended. 

Openings made for future use in the present roof 
should be covered with temporary removable slabs. The 
customary way is to build the floor with ledges for sup- 
port of the slab which is cast in a separate operation. 
The slab will be easier to remove if its contact surfaces 
are lined with building paper and if the vertical surfaces 
around the slab are given a slight draw. For removal of 
a temporary slab, holes may be provided when concrete 
is placed or may be drilled in it for lifting attachments. 
Or the slab may be raised from below. 


14. EXTENSION OF BUILDINGS 


Extension of a building in plan may be carried out 
with speed and ease if a few simple provisions are incor- 
porated in the original design. 

It has been customary to provide for longitudinal 
extension by means of brackets on the temporary end 
columns as illustrated in Fig. 35. Under such conditions 


DOWELS, GREASED 
OR PAINTED 


STGELARLAT E: 
GREASED OR PAINTED, 
ANCHORED TO COL. 
WITH STRAPS 


BRACKET FOR 
FUTURE BEAM 


PRESENT COLUMN 


Fig. 35. Brackets on columns for future extension. 


both columns and footings on the boundary line be- 
tween old and new construction are designed for the 
total final load. The bracket bearing surface should be 
covered with a steel plate, and dowels may be extended 
from the old construction as indicated. All exposed steel 
should, of course, be protected against corrosion. 

The type of detail described has some drawbacks, 
especially in buildings with spread footings supported 
on ordinary subsoil which is loaded nearly to its 
capacity. Vertical or horizontal movement may cause 
damage in the joints between the old and new construc- 
tion. The movements may be caused by unequal settle- 
ment of footings and perhaps also by non-uniform vol- 
ume change. 


Settlement of spread footings generally progresses 
slowly for some time. At the time a new extension is 
built, footings may have stopped settling under the 
old building, but they will go through the regular course 
of settlement under the new building. The result is non- 
uniformity in settlement of old and new building which 
causes movement and possible damage to the joints. By 
keeping the pressure on the soil well within its bearing 
capacity, differential settlement will be small and the 
possibility of damage at the joining of new and old 
construction will be minimized. 


It is best, of course, to provide a complete separation 
between old and new construction by means of expan- 
sion joints extending across the entire structure. There 
should be a complete frame of columns and beams on 
either side of the expansion joint but no structural con- 
nection between the two frames. Movements in the 
joint will then do no harm. 


fps 
| NEW BUILDING UNIT 


PRESENT BUILDING UNIT 


Fig. 36. Customary arrangement of footings designed for 
expansion of building. 


With the usual type of column arrangement, illus- 
trated in Fig. 36, footings at the boundary between 
old and new construction are built large enough to 


NEW BUILDING UNIT 


l 
| 
1 ae se 
I fees! T i 


PRESENT BUILDING UNIT 
t- 


Fig. 37. Footings at expansion joint, columns staggered in 
old and new building unit. 


carry the total final load. Fig. 37 illustrates how to 
take advantage of the diagonal arrangement of columns 
discussed in Section 5, see especially Fig. 15. The 
columns are offset on either side of the expansion joint 
in Fig. 37, the footing under each column is designed 
to carry only the load from the column it supports, the 
bearing pressure is uniform throughout, and the new 
structure is entirely independent of the old. 


The temporary end wall in the old building may be 
left in place to serve as a fire wall when the new build- 
ing is added, or it may be removed. In the latter case, 
a concrete block wall will give good service and if 
properly painted will harmonize well with the appear- 
ance of architectural concrete or structural concrete 
used for spandrels, piers, beams or columns. If the wall 
is to be removed, upturned spandrel beams should not 
be used in it. If the wall is to be left in place, however, 
it may be built as any other exterior wall, but pro- 
vision should be made for future openings for doors, 
pipes and conduits. 


Expansion joints in floors may be built as illustrated 
in Fig. 38. The concrete edges are protected with edge 
angles, the opening is plugged with a compressible 
material and closed at the bottom with a flexible copper 


29 


GROOVE FILLED 
WITH MASTIC ——~ 
SORE 7 oo ie ds 


“T-% CORK OR 
‘CF BER BOARD 


tA 
ma ay 
A ara 


FLEXIBLE COPPER STRIP 


Fig. 38. Expansion joint detail for concrete floor. 


strip. The groove formed at the top of the joint is filled 
with mastic.* 


15. EXPANSION ANCHORS 


New attachments may be made to old concrete sur- 
faces by means of screws or bolts held firmly in place 
by “expansion anchors”. Many excellent types of ex- 
pansion anchors are available, but only a few of them 
will be described here in connection with methods of 
installation. The types presented are chosen to illustrate 
a general discussion, and their inclusion does not infer 
any special recommendation. 

Holes slightly greater than the expansion anchors to 
be used are first drilled into the concrete. An expansion 
anchor suitable for a screw connection is illustrated in 
Fig. 39 and for a special type bolt connection in Fig. 
40. In both of these anchors, a cone of hard metal with 
scored surface is placed inside a sleeve usually made of 
a lead composition. The shape of the lead sleeve is 
shown cylindrical but may also be conical. The assem- 
bly of cone and sleeve is inserted in the hole drilled for 
it, and a setting tool which is placed against the lead 
sleeve is given a few sharp blows with a hammer. This 
makes the lead sleeve expand and stick in the hole. 
The part to be fastened to the concrete is then placed 
over the expansion anchor, the screw or nut is attached 
and pulled up tight. The metal cone is thus forced into 


SPECIAL 


SCREW 
BOLT 


LEAD SLEEVE>: 


Fig. 46. Expansion anchor 
for bolt connection. 


Fig. 39. Expansion anchor 
for screw connection. 


30 


Fig. 41. Expansion anchor with 
lead sleeve and lead cone. 


the lead sleeve which expands so that it fits tightly in 
the hole. 

The assemblies in Figs. 39 and 40 may be enlarged 
by including two cones and two lead sleeves. An assem- 
bly with two cones, one of which is of lead composition, 
is illustrated in Fig. 41. A special type of bolt is required 
for the assembly both in Fig. 40 and in Fig. 41. 

Regular machine bolts may be attached to concrete 
by means of expansion anchors made as illustrated in 
Fig. 42. The anchor consists of a collar of ductile metal, 
made very thin at the middle. The depression in the 
collar is filled with lead so as to give the collar a smooth 
cylindrical surface. Thus the collar is in effect a double 
cone similar to the assembly in Fig. 41. The outer cone 
in both Figs. 41 and 42 is spread by sharp blows on a 
setting tool placed around the bolt shaft. The inner 
cone will make the lead sleeve expand when the nut is 
pulled up tight on the bolt. 

The grip obtained by an expansion anchor is approxi- 
mately equal to the tensile strength of the bolt or screw 
used. It is not necessary to drill the hole to exact depth, 
and some lateral adjustment is possible in expansion 
anchors since the bolts are surrounded by lead compo- 
sition and therefore can tilt slightly while attachment 
is being made. 

In case a lateral displacement of the bolt must be 
avoided, a thick circular metal washer is added to the 
anchor assembly. The washer is slipped over the bolt 


' and lodged securely in the drill hole on top of the 


anchor but below the floor surface. 

Attachment to floors by means of expansion anchors 
is accomplished easily and rapidly. Even in new con- 
struction many builders like to finish concrete floor sur- 
faces without setting any floor bolts. They prefer to 
come back and drill holes later for expansion anchors 
in the floor. Expansion anchors may be placed in ceil- 
ings and walls also, but here it is preferable to use 
inserts. 


*For similar details of expansion joints reference is made to 
the booklet Concrete Bridge Details (see Fig. 28) and to Expan- 
sion Joints in Concrete Buildings (see Figs. 6, 7 and 8). 


SE 


eos: ie s 5 eee 


SPECIAL ‘ bare a> 
ECIA BOLT 
LEAD CONE aoe 
LED oi DUCTILE 
a A: METAL 
Leap - d a! | LEA 
SLEEVE © ue FILL 


Le 


Ses 
Noe 
tig? 
“OA 


Fig. 42. Expansion anchor 
for ordinary machine bolt. 


16. INSERTS 


An economical and practical method of making 
attachment both to ceilings and to walls is by means of 
inserts. Inserts may be described as metal casings the 
inside of which is designed to receive various kinds of 
screws or bolt heads. The metal casings are usually 
made so that they can be fastened to the concrete 
forms, and they are left securely anchored in the con- 
crete when the forms are removed. There are many 
suitable inserts available, and the fact that only two 
of them are illustrated here should not be taken to infer 
any special recommendations. 


Fig. 43. Insert for 
screw connection. 


Fig. 44. Insert for 
bolt connection. 


walt 


Y. 
7 


Principal features of inserts are illustrated in Fig. 43, 
designed for a screw connection, and in Fig. 44, de- 
signed for a bolt connection. Both types have the fol- 
lowing characteristics in common. One face of the insert 
is plane and has two small holes or notches for nailing 
the insert to the form. The nailing is an important fea- 
ture since it makes attachment easy but dislodgment 
difficult. The plane face has an opening for insertion of 
screw or bolt. The opposite face is designed to give the 
insert secure embedment in the concrete. It must de- 


31 


Opening in floor of Albert Pick Company plant is designed for a 

metal spiral chute. Attachment of chutes and of railing bases may 

be made speedily by screws or bolts fastened to expansion anchors 
set in holes drilled in the concrete. 


velop enough anchorage so that the insert will not be 
pulled out under a tension smaller than the capacity of 
the screw or bolt for which it is designed. 

The inside of the insert in Fig. 43 is simply a threaded 


Vertical movement of goods by gravity on spiral chutes solves the 
transportation problem in the Walgreen Company plant, Chicago. 
Even glass and china are moved speedily, safely and without inter- 
ruption from floor above to floor below- 


sry 


m 


XS 


S55] 
SORES 
$O525<052 


5 
se, 


‘> 


So 
S350 


Overhead equipment is fastened to ceiling by means of a timber 

base attached by bolts to the concrete. Attachments can be made 

rapidly when a sufficient number of ceiling inserts have been pro- 

vided originally. The building was designed by A. Epstein for 
Albert Pick Company, Chicago. 


hole made for a screw. Sizes larger than 3 in. are not 
usually available. Screw inserts are used for suspension 
of sprinklerpipes and other relatively light overhead 
equipment. Since no lateral adjustment is possible in 
screw inserts, hangers for pipe lines should be made 
adjustable in both horizontal and vertical directions. A 
swivel and split-ring type of hanger gives good service. 


Inserts of the type illustrated in Fig. 44 are designed 
for bolt sizes up to 1 in. Some of them take a regular 
bolt head while others require bolt heads of special 
shape. In general, the bolt head is inserted through the 
larger part of the opening and then moved horizontally 
so that the bolt shaft extends through the slot while 
the head bears on the inside edges. It is desirable that 
lateral movement of the head should be prevented after 
the attachment has been completed. The bolt heads 
may be lodged securely in various ways. A certain 
amount of lateral adjustment of the bolt is possible 
within the insert. Some slots are made up to 6 in. long, 
and a bolt may be placed anywhere within this distance. 


It is good practice to seal or grease the inside of in- 
serts before they are placed in order to keep out cement 
paste and to avoid corrosion. 


Under certain circumstances, continuous ‘anchor 
slots’ are used which incorporate the same anchorage 
features as inserts but make it possible to make attach- 
ment at any point along the slot. They are especially 
useful when placed in concrete columns or walls for 
anchorage of partitions or furring. 


Attachment of furring to concrete walls may be made 
by means of anchor slots, wire loops, wood plugs, nail- 
ing inserts, strap anchors or by special patented devices. * 


It is good practice to use plenty of inserts in all ceil- 
ings in factory buildings so that attachments can be 
made anywhere at any time. It is recommended to place 
an insert every 4 ft. in both directions. If this is done, 
it will seldom be necessary to drill holes in the ceilings 
for expansion bolts. 


32 


17. PIPE SLEEVES IN NEW 
CONCRETE FLOORS 


Expansion anchors and inserts, discussed in Sections 
15 and 16, furnish useful and convenient ways of pro- 
viding for equipment of non-permanent nature, that is, 
equipment which is not essential to the operation of the 
building itself. Permanent equipment such as sprinkler 
system, plumbing and heating pipes should preferably 
be installed by means of pipe sleeves in the concrete 
floors. 


Small circular open- 
ings through concrete 
floor slabs may be 
made by means of or- 
dinary stovepipe. One 
end of the pipe is slot- 
ted and spread out to 
form a base as illus- 
trated in Fig. 45. The 
base is nailed firmly to 
the slab forms, and the 
pipe is filled with sand 
before the slab is con- 
creted. 

In some instances, 
such as in roofs de- 
signed for use as future _‘ Fig. 45. Pipe sleeve for circu- 
floors, it may be de- lar hole in concrete floor. 
sirable to provide for 
a future opening without having a hole in the present 
slab surface. In order to do this, make the pipe 1 to 2 
in. shorter than the slab depth and cover the top of the 
pipe with a cap. The hole may then be broken through 
easily whenever required. 

Spaces between pipe sleeves and pipe risers, and also 
holes provided for future use should be plugged with an 
elastic compound to prevent leakage. 

The use of small pipe sleeves for through bolts is 
illustrated in Fig. 46. Standard bolt heads will not cause 
interference if they are on the ceiling; but on floors, 
bolts with button heads should be used. 

Cast iron pipe is often used, especially for sprinkler 
pipe risers. Such risers are placed as close as possible to 


*For details and further discussion of furring see Furring 
for Architectural Concrete Walls. 


SHEET METAL SLEEVE “Yy 


Vz 
WNEZINAAN ~— 


Fig. 46. Pipe sleeves for bolting permanent equipment. 


CAST IRON 
Pine SHEE Sic 


age ecnn ateneislen see 


‘COLUMN ~ 


Fig. 47. Cast iron 
pipe sleeve at col- 
umns. 


PLUG OPENING ~ 


columns and therefore extend through the drop panel 
and capital of flat slab construction. One end of the pipe 
sleeve is shaped as shown in Fig. 47 to conform to the 
contour of the capital. The diameter of this opening 
should not exceed one-twentieth of the average panel 
length in flat slab construction. 

Even where no pipe risers are required at columns in 
the original layout, it is still a good plan to provide one 
large pipe sleeve at every column as illustrated in Fig. 
47. Since the opening should be plugged anyway, it is 
even better to terminate the cast iron sleeve about 2 in. 
below the floor surface, provide it with a cap, and let 
the concrete cover the top of the cap. 


18. NEW HOLES THROUGH 
OLD CONCRETE SLABS 


The most common method of making new holes 
through old concrete slabs is by use of star drills. Hand 
drilling is used mainly for small holes down to 14-in. 
diameter, but power drilling is necessary for the larger 
holes up to 2-in. diameter. Star drills are seldom used 
for diameters larger than 2 in., and they will not cut 
through reinforcing bars. 

If in drilling a hole the operator hits a bar, he should 
remove the drill to another point about 2 in. away from 
the first hole. If the second hole is drilled at any one 
of the points marked A in Fig. 48, there is an even 
chance that the drill will hit a bar also the second time. 
It is better to move the drill in the diagonal direction 
to any one of the points marked B, where the proba- 
bility of hitting a bar is slight. 

In drilling from above through the entire depth of 
the slab without taking special precautions, the con- 
crete may spall on the underside as illustrated in Fig. 
49. This can be avoided by first drilling into the ceiling, 


-— HOLE BEING DRILLED 


ee al ae ee 


CONCRETE SLAB 


WEDGES ~ 


TEMPORARY 
EHORE a 


Fig. 49. Drilling through concrete slab. 


to a depth of about 2 in., a hole slightly larger than the 
hole which is drilled from above. This may be a cumber- 
some procedure, and it will be easier to drill the entire 
hole from above, exerting sufficient pressure against the 
ceiling at the hole during the drilling to prevent spalling. 
One way to do this is by wedging a shore between the 
ceiling and floor as indicated in Fig. 49. 

For larger holes, the method of “‘coring’”’, used suc- 
cessfully in highway work, may be employed. The pro- 
cedure developed for highway work is essentially as 
follows. The “‘drill’”’ consists of a seamless steel tubing, 
which is available in various diameters. One end of the 
tubing is closed with a metal disk to which a drive 
shaft is attached. A notch is cut in the other end as 
illustrated in Fig. 50, but the cutting edge is neither 
sharpened nor treated in any other way. The actual 
cutting is done not by the edge of the tubing but by 
small “shot”? made of chilled steel. To get the cutting 
started, it is necessary to pour the shot into a circular 
groove formed as illustrated in Fig. 50. The concrete 
must be kept wet in the cutting groove. The tubing is 
rotated at a fairly slow rate of speed between 50 and 
100 r.p.m. It is possible to cut through reinforcing bars 
in this way. Holes cut by the coring procedure described 
are generally made from 4 to 6 in. in diameter, but 


DIRECTION OF|SLAB REINFORCEMENT 


INCORRECT CORREGI 


Fig. 48. Locating drill holes to miss reinforcement in con- 
crete floors. 


33 


SEAMLESS 
STEEL TUBING 


SMALL CHILLED 
STEEL SHOT IN 
CIRCULAR GROOVE 


ESSUAB eis) Oi een eee 


Fig. 50. Coring through concrete slab. 


larger holes may be made with proper equipment. 

Openings may also be made through concrete slabs 
by means of a rotating saw consisting of a circular steel 
disk with a carborundum cutting edge. The steel disk is 
rotated at a high speed, about 5,000 r.p.m., and cuts a 
groove while being moved slowly back and forth on the 
concrete. It will cut through reinforcing bars. The depth 
of the groove depends upon the diameter of the cutting 
disk. In cutting a rectangular opening as in Fig. 51, it 
is well first to drill or core one hole at each corner of 
the opening and then saw through the slab. 


19. INSTALLATION OF ELECTRIC 
CIRCUITS 


A distinction is often made in factories between elec- 
tric circuits for permanent and for non-permanent pur- 
poses. Permanent installation includes lights, fans, ele- 
vators, power-operated doors and column outlets. Con- 
duits and outlet boxes for permanent installation are set 
by the electrical contractor before the concrete is placed. 
They are nailed to the form boards and remain embed- 
ded in the concrete when the forms are stripped. 

Power lines for machines may be run in exposed cir- 
cuits installed by the plant electrician any time after 
completion of the concrete structure. The plan of run- 


34 


SAW CUT 


CORING HOLE 


Fig. 51. Cutting large opening in concrete slab. 


ning power lines concealed in the structure may give 
better appearance when the structure is new, but there 
are likely to be new out-croppings of exposed lines when- 
ever the production layout is changed. The lines may 
as well be exposed from the beginning. They can be 
attached to ceiling inserts or to small expansion anchors. 

Some designers run ducts for power lines the full 
length of the factory building along the inside of the 
wall. The ducts may be placed at the base of the wall, 
the duct to the ceiling. Fig. 52 illustrates this arrange- 
ment which is particularly satisfactory when the span- 
drel beam is of uniform width. The duct should have 
detachable bottom or side so that the plant electrician 
at any time and at any point can open the duct and 
make the desired connection. The main and the cross 
ducts illustrated may be attached to ceiling inserts. 

In factory offices with many electrically operated 
small machines the exposed ceiling ducts with wire 
dropped down to working level may be objectionable. 
However, it is possible to install under-floor ducts in a 
2-in. concrete topping. The ducts are concealed, and 
connections can readily be made at any time. 

A good rule to follow is to install lamp outlets not 
farther apart than the height from floor to ceiling, and 
also to provide D.C. and A.C. power panels on alternate 
columns. It is essential that the wire be of suitable size 
in order to avoid the expense of re-wiring a factory 
building. A 100-watt lamp may be adequate in a ware- 
house, but it may take 300 to 500-watt lamps for fine 
machine work. Opportunities for improvement of arti- 
ficial illumination by painting the concrete ceilings 
should be carefully considered.* 


*For details and recommendations reference is made to Paint- 
ing Concrete. 


SPANDREL BEAM 


MAIN DUCT 
WALL COLUMN 


Fig. 52. Ducts for electric conduits attached to flat slab 
ceiling. 


WIDTH OF RAMP OR DRIVEWAY 


GARAGES 


20. DIMENSIONS OF AUTOMOBILES 


FROM year to year, the manufacturers of automobiles 

make minor changes in dimensions of new car models, 
but in general the dimensions in Fig. 53 represent a 
fairly uniform standard practice which may be used for 
layout of garages. 

The tread, 7, is practically the same for all cars. 
Other dimensions vary from model to model, usually 
within the limits given in Fig. 53. Width, height and 
length are overall dimensions of the car body itself. 
Wheel base and turning radius are the dimensions 
marked W and R in the diagram. 


/ANSIDE OF CURB 


It is often necessary to make a study of a curved 
ramp or driveway in garages in order to establish mini- 
mum dimensions for width and curvature. Fig. 53 con- 
tains a sketch showing how to determine such dimen- 
sions. The heavy lines are sides in a right-angle triangle, 
in which W and R are known. 

Determine R- E = VR? — W?, and insert known 
values for R and W. Then establish width and curva- 
ture of ramp on basis of R, E, T and the clearances, 
D and F, that are considered necessary for operation. 
D = 1 ft. and F = 1 ft. 6 in. are considered minimum. 


21. LAYOUT OF PARKING UNITS 


Garages to be erected on property of limited extent 
present an important problem in layout. Numerous 
small parking units, or car stalls, must be arranged in 
certain patterns so that the finished garage is easy to 
operate and profitable to its owner. 

The parking unit itself is fairly well standardized. The 
minimum width of parking space for one car is 7 ft. 6 in. 
A width in excess of 8 ft. 6 in. is considered a waste of 
space. Three cars parked between two columns require 
a clear distance of 22 ft. 6 in. This dimension may be re- 
duced to a minimum of 22 ft. in lower stories, in which 
columns are likely to be larger than in stories above. 
Clear distance between columns is frequently increased 
to 24 ft. or more for a group of three cars in garages 
where owners park their own cars or where parking is 
of short-time duration such as in garages for shoppers. 

The three-car bay is the unit that is used most fre- 

quently, and permits the parking of two 
trucks in a bay. Certain advantages are 
claimed for a two-car bay, but the ten- 


TYPICAL DIMENSIONS OF PASSENGER 
AUTOMOBILES USED IN LAYOUT 
OF COMMERCIAL GARAGES 


TREAD, T AVERAGE 5-0" 
WIDTH 5"-11" TO G-10" 
HEIGHT 5'4"TO5+10" 
WHEEL BASE,W  9°6"TOI2:0" 
LENGTH 15-0" TO 20-0" 


TURNING RADIUS, R:20:0" TO 30:0" 


Fig. 53. Dimensions of automobiles and layout of curved ramps. 


IB-Ore 22-0. 18-0" 


dency is to use two and four-car bays 
only where necessary to make parking 
units fit ramp layout or property lines. 

The depth of a parking unit is usually 
18 ft., and aisles between parking units 
are 22 ft. Two rows of cars with one inter- 
mediate aisle require a total width of 58 
ft. as illustrated in the first sketch in 
Fig. 54. The 58-ft. dimension is the clear 
distance between walls or spandrels. 


58-0" INSIDE WALLS 


16-0" INSIDE WALLS 


EOx +O” "On 0" ple. aeemnce One O07 1670 yr 22-07 p00: 
18-0 clits O 212-0 18-0 ale cll Ab |. +. 
116-0" INSIDE WALLS 


Fig. 54. Layout of parking units. 


35 


These dimensions are a little cramped for extra long cars. 
Such cars may conveniently be parked at ends of aisles 
where encroachment on aisles is of little consequence. 

The second sketch in Fig. 54 shows the type of park- 
ing arrangement that may be used for a 76-ft. clear 
width. There is single parking on one side of the aisle 
but double parking on the other side. In other words, 
one-third of the parking area may not always be readily 
accessible. Yet, the arrangement may work well in some 
instances, and in others there may be no other choice 
for a lot of such limited width. 

The third sketch in Fig. 54 shows four rows of park- 
ing, a scheme suitable for a 116-ft. clear width. All 
parking spaces face an unobstructed aisle. This layout 
is commonly used, but there are instances in which all 
three layouts illustrated may be combined with each 
other or with other layouts not shown. Each site pre- 
sents a different problem in layout. 


Concrete ramps carrying truck traffic from floor to floor 

in the Chicago Carton Company plant provide easy and 

uninterrupted vertical transportation of materials. The 

concrete ceiling has been painted to improve illumination 
on the ramp. 


WITH MASONRY WITH CONCRETE WALL 


CURTAIN WALL 


SECTION A-A SECTION B-B 
(rare CURTAIN Menor : CENTER LINE MASONRY CURTAIN ea 

18 PARKING ISLE IB'PARKING ¢ J8'PARKING U2 AISLE 18° PARKING 
a + i 4 * : 


GIR 


Cr OFFSET 


22. FRAMING PLANS 


One of the first problems in develop- 
ing a framing plan for floors concerns 
the placement of columns. Columns 
should generally be spaced to allow not 
more than three cars in each bay. The 
column centerline 
may be set back 2 to 3 
ft. from the aisle, and 


MAX. COL. WIDTH: }°@” 


the column width 
should not be made 


al 
tt 


more than 1 ft. 6 in. 
If necessary, the 
column cross-section 
may be oblong. 
Column corners 
should be beveled or 
preferably rounded. 


8-6" 


8-6 


Guard curbs are not 
needed around column 
bases, but a thin 
guard plate is useful 
around the bottom of 
columns up to just 


tt 
| eee ae Le | | ee 


[ @: 


Ble 


ee | fl ee | 
i ie. 
Gal lia-cil oc: 
oe 


= 


above the level of 
bumpers. 


The placement of 


Fig. 55. Beam and girder framing, 116-ft.-wide garage. 


36 


columns in Fig. 55 
represents a_ typical 


layout for a 116-ft.- fer erne WALL 
wide garage. The -+- ue ee 
column spacing is 25 
ft. 6 in. in the longi- 
tudinal direction, al- 


CENTER LINE CONCRETE WALL > 
22 AISLE , IB PARKING f 18 PARKING ! 22° AISLE ! 18 ' PARKING 
po 


| 
eee eee 


=. 


Ofeetit..0*in. for 
three cars, and 29 ft. 
in the transverse 
direction. The use of 
bays with equal width 
has the advantage of 


| 

been 
lowing a clear width _ 

| 

| 


_— 


-{- 


See abe | 


-- = 
By 


| 
| 
ene 


a 


| | 
eyo ead ——— 


simplifying the con- 
struction of forms and 4” 
the fabrication of re- | 


t 
Lo 


| 
| 
ea 
\ceae8) Shee ae ff 


oa Se eee 


| | | 


inforcement.After a 

: , 10" 14°6" 29-0 279-0" 29-0" db -6" | 
having established the 2 om. 
panel size of 25 ft. 6 onO 
In. by 29 ft. 0 in., the Fig. 56. Two-way solid slab framing, 116-ft.-wide garage. A-A and B-B similar to Fig 55. 


choice of floor framing 
has been limited to 
certain types, three of 
which will be dis- (CCXCRETE WALL 


PARKIN 
cussed. Abies ae 


Fig. 55 shows a 
beam and girder fram- 
ing. The floor slab has 
its main reinforcement 
in the longitudinal 
direction and spans 
between beams sup- 
ported on girders. It is 
advantageous to make 
the girders the same 
depth as, or 1 in. 
deeper than, the 
beams. The 1-in. dif- 


CENTER LINE 
18 PARKING, f 18 ARNG 


ze AISLE 18/PAR 


CONCRETE WALL) 


LZeAIOLE 18' PAR KING} H 


79-05 


ference in depth is _!Q) 14-6" 
preferred because in- 


116-0" 


terference of bottom 
bars is then avoided. 
The shallowness of the 
girder cuts down the height of the structure. The bays 
outside the exterior columns are cantilevered from the 
interior floor construction. Spandrel beams and wall 
construction are supported on the ends of the canti- 
lever bays. 

The same panel size of 25 ft. 6 in. by 29 ft. 0 in. is 
used in Fig. 56. The ratio of long to short span, 1.14, 
is suitable for a two-way solid slab floor framing as 
illustrated. The beams shown are wide and shallow, 
but deep narrow beam webs may of course be substi- 
tuted. In both cases, the longer beams should preferably 
be 1 in. deeper than the shorter beams. The outer nar- 
row bays are here, as in Fig. 55, cantilevered and sup- 
port spandrel beams as well as other wall construction. 

The third floor framing illustrated for a 116-ft.-wide 
garage is a two-way flat slab floor system. General fea- 
tures of flat slab design have been discussed in Section 


Fig. 57. Flat slab framing, 116-ft.-wide garage. 


3. The three center bays in Fig. 57 may be designed as 
typical interior panels, and the narrow outer bays are 
designed as cantilevers supporting their own and the 
superimposed load in addition to the load of the wall 
construction. 

If no columns are desired in the parking space, the 
layout in Fig. 58 gives a good framing. It has three rows 
of columns, one in each of the two walls and one along 
the centerline of the building. The column spacing in 
the longitudinal direction is shown as 24 ft. 0 in. 

Since the girder span is relatively short in Fig. 58, 
the girder depth can be made equal to or, preferably, 
1 in. deeper than the beam depth. The layout is shown 
with three beams for each bay. A layout with four 
beams per bay may sometimes be better. Tapered ends 
are often required on beams, especially at the center 
girders where shear and compression may be high. 


37 


ee WALL PCENTEP. LINE Se ae ie Vee 


: IB' PARKING T2EANS GE 1B’ PAIAKING Ea 2 AISLE Es SE 
toes 


Fig. 58. Beam and gir- 
der framing, two 58-ft. 
spans. 


0" 


23. RAMPS 


In multi-story garages, a car is generally moved from 
floor to floor under its own power on ramps. Types of 
ramps may be grouped under the following general 
headings: 


'| ABOUT 3 


Ordinary incline, straight-run 

Curved or spiral 

Staggered floor 

Pitched floor 

Combinations, such as straight and curved 
combined 


SECTION A-A SECTION B-B 


*For analysis of rigid frames, reference is made to Handbook of 


In pode ph tances, a twO-sp an rigid frame layout mY Frame Constants and One-Story Concrete Frames Analyzed by Mo- 
also give satisfactory solution for framing in a 116-ft.- TeniDiinbolon 


wide garage with three rows of columns. Further 

discussion of this type of framing will be given in con- 

nection with a 58-ft.-wide garage. CONCRETE WALL CONCRETE thar 
Fig. 59 shows a 58-ft. garage with a row of columns 18 MINE 22’AISLE ae PARA ae 

in each wall. The spacing of columns is shown as 24 ft. 


0 in. The floor design system is a joist construction 
formed by means of tapered metal pans. The joist floor 


system is supported on girders which are cast integrally 
with columns at both ends. Girder and columns form a 1 i erincrmrem ce cs 
rigid frame and should be designed as such.* A hori- 


zontal thrust is created by the rigid frame at the base 


0” 


of its vertical members. The thrust, giving tension in 
the floor members, should be taken care of in the floor 
design. Columns should, of course, be designed for com- 
bined bending and axial load. 

A clear story height of 8 ft. is ample for ordinary 


24 


cars, but more is required for trucks. A good arrange- 

ment is to use 8-ft. clear height in upper stories, but to 

use greater height in the first story where trucks may 

then be parked. 10” 
A superimposed load of 100 p.s.f. is ample for all pas- 3a 


senger cars, and 150 p.s.f. is sufficient for most trucks. Fig. 59. Rigid frame layout with metal pan floor. 


38 


Many patents have been taken out on ramp systems 
and ramp features. For a good discussion of this sub- 
ject, reference is made to ““The Layout of Automotive 
Buildings’ by H. F. Blanchard, published in the 
Architectural Forum, March, 1927.* 

Determination of width and curvature of circular 
ramps has already been illustrated in Fig. 53. It should 
be noted that such ramps cannot be built in garages 
that are narrower than 60 ft., a dimension that is 
established by the turning radius of a car. 

The ramp grade is made anywhere from 12 to 20 
per cent, the average being 15 per cent. Ramps should 
have curbs at the edges, and it is good practice to make 
the curbs conspicuous by painting them black and 
white. 

Ramps should, of course, have suitable banking and 
easement curves. The surface should be a rough, 
broomed finish, or a non-slip aggregate finish may be 
used. Transverse grooves in the top surface of either 
ramps or floors are not recommended anywhere in 
garages. The grooves may collect oil or grease, which 
tends to make the surface slippery. 

The structural framing of ramps depends largely on 
type of ramp and layout of garage. It is customary to 
use solid concrete slab on beam construction. The 
building of forms requires superintendence by an expe- 
rienced man. Placing of reinforcement and concrete is 
similar to that for pitched roofs. Good care should be 
given to mixing and placing concrete, but there are no 
unusual features involved. 


24. STRUCTURAL DETAILS 


During winter months it often happens that cars are 
driven into a garage while they are covered with ice 
and snow which melts in the warm garage. Water cover- 
ing an improperly constructed floor may then leak 
through small cracks and drip down on cars parked 
below. This trouble can be avoided by giving proper 
attention to structural details. The discussion that 
follows applies to all exposed concrete floors through 
which leakage must be avoided. 

Cracks at construction joints sometimes open enough 
to permit leakage. This can be prevented very largely 
by proper details. It is recommended that construction 


PLAN 


1. BAR OMITTED 
ZaDARSYLELDS 


Sit Gin GO NEASA 


Fig. 61. Cracks caused by negative moments. 


joints in garages should be marked plainly on the draw- 
ings, and that no joints other than those shown should 
be permitted. Extra reinforcement should be placed at 
right angle to the joint and should extend at least 50 
diameters on each side. The area of the extra rein- 
forcement should be not less than 0.003 times the con- 
crete area in the joint. This precaution will serve to 
minimize cracking, but it may be desirable to require 
also that a 14-in.-deep “‘cut’’ be made in the top sur- 
face of the concrete in the joint (see sketch, Fig. 60). 


a c 
“DEEP CUT ce. ou 
H PLASTIC FILLER): 
sie gh ee 
Vo 5 Ste EXTRA BARS 
Oe eae 


SLAB REINFORCEMENT ~CONSTRUCTION JOINT 


! 
rs 
Tt 


Fig. 60. Construction joint in garage floor. 


If this is done, and a crack should develop in the joint, 
leakage may be prevented by simply calking the cut in 
the joint. Another solution is to avoid construction 
joints altogether or to place them where leakage can 
do no harm. 

Cracks caused by negative moments are less likely 
to open sufficiently to permit leakage than construction 
joints. A “negative” moment creates tension in the top 
surface of the floor. Top bars for negative moments are 
frequently either too short or too small, or are omitted 
entirely at end supports. Section A-A in Fig. 61 illus- 
trates these defects. If a top bar slips (too short) or 
yields (too small), a large crack may open through the 
slab and permit leakage. Fig. 62 illustrates the correct 
and the incorrect way of detailing bars at spandrel 
beams. Leakage will be avoided by providing top rein- 
forcement with sufficient area and length. 


*For further references, attention is called to the following 
publications which deal not only with ramps but also with other 
items of importance in design and layout of garages: 

Garages, Standards for Design and Construction, 

Architectural Record, Feb., 1929, p. 178. 

Ramp Problems in Garages, by K. F. Jackson, 

Architectural Forum, April, 1928, p. 599. 
Automotive Buildings Reference Number, 
Architectural Forum, March, 1927. 


~ TOP BARS 
5-3", HOOKED 


TOP BARS AT ALL CORNERS 


39 


CRIAG Kea 


INCORRECT 


Fig. 62. Correct and incorrect bar details at spandrel beams. 


The possibility of cracks at the corners of openings 
in floor slabs can be minimized by placing diagonal bars 
at each corner. Each group should have not less than 
three 54-in. round bars 5 ft. long. The designer should 
study the framing plan together with all openings 
through floors with the view of providing extra rein- 
forcement across planes that may crack. 

Where the top slab of metal pan floor construction is 
made too thin and under-reinforced, cracks may occur. 
It is recommended for such floors that the top slab 
should be not less than 3 in. thick and reinforced with 
not less than 3-in. round bars spaced 12 in. on centers. 
The bars should be placed in the top of the slab. 


25. ELEVATORS, STAIRS 
AND ROOFS 


As has already been mentioned, circular ramps can- 
not be built in garages with a width less than about 
60 ft. In small garages, say 50 ft. wide, the-use of ele- 
vators may be fairly satisfactory for moving cars up 
and down. This is especially true in service garages and 
in other garages where the peak load is small. 

Car elevators are usually made 10 ft. wide, 20 ft. 
long and 8) ft. in clear height. They are often placed 
in the back of the garage, and it may be convenient or 
even necessary to have a turntable in front of the 
elevator. 

Passenger elevators and stairways may be placed in 
a corner or in any other convenient bay. Fig. 63 is a 
typical layout showing how to accommodate both ele- 
vator and stairway in a bay two cars wide. The spacing 
of columns adjacent to the stairs should be 15 ft. center 


Printed in U.S.A. 


G@ RRS Gly 
P Ree 20-0" 
CAR 
eee, 
= | CAR 
. [a 
Og 
-t <— 
ea) i) 
ra 
= iRCAR 
Gi rsrm 
| kefe 9 
CAR 
12-6" 25-0" 


Fig. 63. Layout for passenger elevator and stairway. 


to center. A 36-in. width is usually suflicient for the 
stairways. Concrete block walls are indicated for the 
enclosure, and steps as well as landings may be of solid 
slab concrete construction. 

It is often a good plan to provide for parking on the 
roof. This may give an extra source of income, and it 
may also facilitate the construction of additional stories 
if the ramp to the present roof level has been built 
beforehand. The roof slab may be covered with regular 
9-ply roofing. The roofing may be protected with a 3-in. 
concrete slab reinforced with mesh and laid in 20x20-ft. 
squares. Joints between squares should be 14 in. wide 
with a plastic joint filler. 


5292 


CONCRETE 
GRANDSTANDS - 


PORTLAND CEMENT ASSOCIATION 


toe 


CONCRETE 
GRANDSTANDS 


The activities of the Portland Cement Association, a national organization, 
are limited to scientific research, the development of new or improved 
products and methods, technical service, promotion and educational effort 
(including safety work), and are primarily designed to improve and extend 
the uses of portland cement and concrete. The manifold program of the 
Association and its varied services to cement users are made possible by 
the financial support of over 70 member companies in the United States 
and Canada, engaged in the manufacture and sale of a very large pro- 
portion of all portland cement used in these two countries. A current list 
of member companies will be furnished on request. 


Published by 


PORTLAND CEMENT ASSOCIATION 


33 West Grand Avenue, Chicago 10, Illinois 


COPYRIGHT, 1948 BY PORTLAND CEMENT ASSOCIATION 


ILLINOIS MEMORIAL STADIUM, MOOSEHEART, ILL. 


The versatility of architectural 
emphasized by the rustication. 


decorative feature. The impressive buttresses at the main entrance mar 
seating arena. F. D. Kay, architect. 


concrete is revealed in these attractive walls in which the horizontality of the design is 
Likewise the fenestration is well integrated with the design as a whole and becomes a 


k the passages through which one reaches the 


TABLE OF CONTENTS 


INTRODUCTION . 
COST 
FINANCING 


THE PROJECT . 
Size 
Shape 
Location 


Facilities 


DESIGN DETAILS A 
Orientation of Athletic Fields . 
Sight Lines . 

Treads and Risers . 
Seats and Seat Supports 
Aisles 

Entrances and Exits 
Stairways and Ramps . 
Walls and Railings 
Fences and Entrances 


Illumination for Night Play . 


FACILITIES 
Dressing and Locker Rooms . 
Dugouts 
Public Facilities 
Concessions 
Ticket Booths 
Offices and Storage 
Press and Broadcasting Accommodations 
Public Address System 


STRUCTURAL DETAILS 
Loads 
Framing 
Expansion Joints . 
Construction Joints 
Watertight Decks . 
Structures on Embankment 
Roofs . 


CONSTRUCTION . 
Quality Concrete . 
Finish 


ACKNOWLEDGMENTS 


Page 


© Spence Air Photos 


Olympic Stadium, Los Angeles, Calif. 
The bowl shape has been used fora 
number of the larger stadiums. John 
and Donald B. Parkinson, architects. 


Dormitory rooms for 1,000 students 
were included asa part of this stadium 
for Louisiana State University, Baton 
Rouge, La. Weiss, Dreyfous and Sei- 
ferth, architects; George P. Rice, 
structural engineer. 


The drawings in this publication are typical designs and should not be used as working drawings. They are intended to 
be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with 
legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. 


INTRODUCTION 


N longer is a modern permanent grandstand a luxury 
to be enjoyed only by the large university or large 
municipality. Today it is a necessary part of the athletic 
plant of every college and high school. Sports are defi- 
nitely recognized as an essential part of the educational 
curriculum, and sports always rightly command an 
audience. 

A grandstand also aids in the development of civic 
interest. Here the students, alumni, parents, friends and 
civic leaders can gather and enjoy a feeling of participa- 
tion in the accomplishments of the local teams. Here 
friendly rivalry can be enjoyed by all. When the field and 
stands are not in use for school purposes, the municipal- 
ity has available an outdoor recreation center for pag- 
eants and civic celebrations. Here honors can be prop- 
erly paid to visiting dignitaries among favorable sur- 
roundings. An adequate place is provided for festivals 
and concerts to the delight of the entire community. 
A center of community interest is established. A grand- 
stand is an essential asset for every community—an out- 
standing American institution. 

Usually the structural design of grandstands is not a 
difficult problem for the engineer. However, proper de- 
tails are important. A large part of this booklet is de- 
voted to the exposition of features which have been 
found to give the best results under working conditions. 
Also discussed are cost, financing, size, shape, location 
and facilities. Consideration is given to the requirements 
of both the performer and the patron. 

The material in this booklet is intended primarily to 
cover small and medium size grandstands for schools and 
municipalities where the principal athletic events will 


TT 7TH LEE i 
T08 Fl GF 
, A ‘ 


i oa 111 ae TT 
Way ii wnt ELI ER) 
TiPieeie 


be football or baseball. However, much of the material 
is applicable to grandstands of any size used for any 
purpose. 


Attractive Grandstands 
With Minimum Maintenance 


Grandstands are continuously exposed to weather, the 
destructive forces of wetting and drying, freezing and 
thawing. It is desirable that they be so built that little 
maintenance will be required to keep them shipshape 
even under these severe conditions. They must, of 
course, be safe against damage or collapse when subject 
to the uncontrollable shocks caused by crowds of excited 
spectators. They should also be fire-resistant. 

Concrete is, therefore, most often chosen for grand- 
stands because it is relatively low in first cost, has the 
ability to withstand weathering with the minimum of 
maintenance, is firesafe, and has a tremendous reserve of 
strength. Beauty may be combined with its utility, since 
concrete lends itself so readily to architectural treat- 
ment. Improvements in form construction and in the 
methods of making, placing and finishing concrete have 
transformed it from a structural material only to one 
that is being used both structurally and architecturally. 
The illustrations in this book show only a few examples 
of its possibilities as an architectural medium. Outside 
walls may be made as elaborate or simple as desired. En- 
trances may be featured with appropriate details, and 
concrete enclosure fences of suitable design to harmonize 
with the main structure may be added to complete the 
project. 


> 


ry y Y a a _— 


‘MQG O00 ER Ane ang an 
HAR GAR GES ENG Onn aan any 
EA SURATTN TON itt 


A es M ly AEE 


Le 
Th Tn Uae i th 


~~ Gee 
| ne 


mh. " mee 


mn i] WE 


ae 
Rin 


ay 


5 


COST 


One of the first subjects which come up for discussion 
in connection with the construction of permanent grand- 
stands is their cost. The cost of the complete project is 
affected by a multitude of items including: condition of 
site—necessary grading, draining, conditioning of play- 
ing field, access drives and walks, fences, public utili- 
ties and foundation conditions; size and shape of grand- 


stand; facilities provided—team rooms, public rest 
rooms, offices and concessions; architectural treatment; 
and local cost of materials and labor. For this reason, 
general figures on cost can have little value. However, as 
a rough approximation the cost of the seats and sup- 
porting structure only may be estimated at about $6 to 
$10 a seat. 


Concrete may be used with any style of architecture. Gothic details are used in the University of Tulsa Stadium, Tulsa, 
Okla. Note flag poles attached to outside of walls and light poles supported on rear of structure. Leon B. Senter, architect. 


FINANCING 


Where there is need for a grandstand, the financing of 
the project should not be difficult. The size and cost of the 
structure may be suited to the local requirements so that 
admission charges will make it self-sustaining and self- 
liquidating where desired. In some cases, of course, 


6 


grandstands are desired where no income will be avail- 
able from entrance fees. These are usually the very small 
stands at public playgrounds, swimming pools or similar 
locations, and their construction is paid for from gen- 
eral funds, or recreation or park appropriations. 


Many methods of financing have been used. A large 
part of the public as well as many educators are of the 
opinion that athletics are now such an essential part of 
a well rounded curriculum that provision for athletic 
structures, including a grandstand as an integral part of 
the school plant, is justifiable. In such cases the grand- 
Stand is built with funds appropriated by the school 
board or the municipality. On the other hand it may be 
necessary to finance the project by public subscription, 
by the sale of securities and by bank loans, or by a com- 
bination of these methods. Where public participation is 
necessary to raise all or a part of the funds, it is essential 
that a well developed campaign be carried on by influ- 
ential people and enthusiasts for the project. 

The first step in a campaign is the organization of a 
promotion committee. A small group of alumni, school 
officials and other citizens may prevail upon the civic 
organizations to appoint representatives to such a com- 
mittee. The committee may incorporate an association 
as a nonprofit organization with the power to lease 
land, to contract for the construction of the grandstand 
and to finance the project. Working capital may be 
raised by donations from a few individuals or by the 
advance sale of season tickets. In some cases working 
capital has been provided by the athletic association 
where such funds have been previously built up. 

The committee must study the requirements of the 
situation to determine the size of the project. An engi- 
neer or architect is employed to prepare preliminary 
plans and sketches for estimating the cost and for use 
in campaign publicity. 

In one city of 25,000 population a local organization 
called the stadium corporation was incorporated under 
state law with the management in the hands of a stadium 
commission composed of 11 members with two members 
representing each of the active civic organizations, the 
chamber of commerce, Kiwanis, Lions and Rotary 
clubs, and three representing the board of education. 
The board of education granted to the corporation a 
99-year lease for the ground. The corporation built 
and is operating the grandstand. 

As a means of securing working capital about $5,000 
was raised by selling season tickets in advance. These 
were sold by members of the organizations represented 
on the commission. Bonds for the construction were 
then issued and sold locally. One-half of all admission 
receipts is credited to an athletic fund to cover current 
expenses of the teams and other running expenses. The 
other half is credited to the corporation and is used to 
pay interest, to retire bonds and to cover incidental 
expenses. When all bonds are retired the lease will be 
surrendered to the board of education and the stadium 
will become its property. 

A well organized campaign for raising funds may be 
conducted by dividing the workers into teams, each 
under the leadership of a captain who is a member of 
the committee or who is selected for his executive ability 
and influence in the community. Each team may be 


A large portion of the cost of the stadium at Mooseheart, 
Ill., was raised by donations equal to the estimated cost 
per seat. Bronze name plates were set in the concrete as a 
permanent record of the subscribers. 


allotted a given quota and prizes awarded for the team 
reaching its goal first or raising the largest total amount. 
Usually prizes are donated by business people for the 
advertising derived. Lists of the alumni should be made 
available for solicitation. Local business people, always 
interested in local improvements, can be depended upon 
to boost the project and help financially. Civic organi- 
zations will take an active part by furnishing workers 
to solicit their own membership and others. 

Publicity is an important activity in a campaign to 
raise funds. The committee should have at least one 
representative who is experienced in this field to take 
charge. Newspapers will cooperate on such projects and 
their publicity may be supplemented by attractively 
designed posters and direct mail pieces. The posters may 
be prepared by students as an art project. Benefit par- 
ties such as dances and card parties, and plays, exhibi- 
tion games and similar entertainments are helpful in 
raising funds and also assist in publicity. Such affairs 
may be conducted by each of the organizations partici- 
pating in the campaign. 


THE PROJECT 


Size 

If the grandstand is to be built in connection with a 
school, the number of students, faculty, alumni and 
local townspeople should be considered. The popularity 
of the school, its athletic relations with other schools and 
the proximity to other towns and cities will influence 
the size. For community projects, careful consideration 
must be given to the drawing power of the events in- 
tended to be held. 

Funds available may determine the size of a grand- 


but these would appear to be special cases rather than 
representative of the average. 


Shape 


Many factors will affect the general shape of the 
structure. A straight or slightly curved stand is suitable 
for football, track and general entertainments. For large 
seating capacities, two such stands can be erected on 
opposite sides of the playing field and where necessary, 
curved sections connecting the side stands can be added 


At Chelsea, Mass., this simple concrete stand was built opposite a larger concrete grandstand, under which are the facil- 
ities for players and spectators. Entrance is directly from the field. Feer & Eisenberg, architects. 


stand. Often where funds are limited, a section of the 
structure is built with a view to enlarging it later. Plans 
prepared for the complete project are helpful in creating 
interest and raising funds for the first section. In some 
cases larger structures than necessary have been built. 
They are, of course, a waste of funds. Where there is 
considerable uncertainty as to the proper size for a given 
project, construction of a grandstand section which can 
be easily enlarged has many advantages. 

A survey of high school grandstands built in com- 
munities up to 50,000 population indicates that the 
ratio of the seating capacity to the population is larger 
for the smaller communities. In towns of 5,000 popula- 
tion, this ratio may be 25 per cent or more while in com- 
munities of 50,000, a ratio of 10 per cent appears to be 
conservative. Using these percentages the structures 
would have 1,250 seats in the one case and 5,000 seats 
in the other. As mentioned above, local conditions will 
affect these suggestions. Examples can be cited of places 
of 30,000 population or more having grandstands with 
seating capacities of 25 to 30 per cent of the population 


8 


to one or both ends. Balconies have been used in a few 
instances to provide the largest possible percentage of 
seats on the two sides of the playing field. In the case of 
football, observations of crowds free to choose their own 
seats show a preponderance of the spectators opposite 
the centerlines and in the lower rows. Some stands in- 
tended primarily for football have therefore been made 
much deeper at the center than at the ends. Grand- 
stands for baseball are built on two sides of the diamond 
with bleacher stands bordering the outfield where neces- 
sary for added capacity. 

Grandstands for a combination of uses are often de- 
sired. The combination of football and track has proved 
very satisfactory but a combination of such uses as base- 
ball and football requires a compromise to the disad- 
vantage of one or the other. Baseball grandstands have 
been used for football by laying out the field with the 
length nearly parallel to one side of the grandstand. 
Football grandstands built on one side of the field have 
been used for baseball by placing the diamond with the 
first base line practically parallel to the grandstand. 


Baseball grandstand at Westfield, Mass. R. P. Boyle, engineer. In small structures such as this, entrance from the field 
is satisfactory and economical. 


Location 


Athletic fields should be readily accessible to players 
and spectators. Ample facilities for parking automo- 
biles within easy walking distance of the entrances are 
highly desirable. At the same time the parking should 
interfere as little as possible with the flow of traffic. 


Facilities 

The facilities to be provided will depend on the size of 
the grandstand, the purpose for which it is to be built, the 
proximity to other structures and the funds available. 
While a small grandstand may consist of no more than 
the actual seating structure, the larger stadiums include 


many special features. Grandstands built adjacent to 
school or other buildings used for athletic events may 
not require dressing accommodations for the teams if 
such accommodations are available in the buildings, but 
in other locations suitable dressing, locker and shower 
rooms should be included or provision made for their 
addition as soon as funds are available. Toilet facilities 
for both participants and spectators should always be 
provided unless available in adjacent buildings. On the 
larger projects, the facilities may also include ticket 
offices and other office space, information, refreshment, 
press and radio booths. Detailed suggestions on facil- 
ities are discussed on page 20. 


Albany, Ga., has this combination football and baseball 
grandstand seating 6,000 people. Due to the hillside loca- 
tion, entrance is from the top. Offices and dressing rooms 
are provided under end sections. The curved front is a 
compromise to adapt the stand to both baseball and foot- 
ball. Rayburn S. Webb, architect; John Lowe, engineer. 


~ 
sys 


i 
§ 
e 
‘ 


The Foreman Field Stadium at Norfolk, Va., illustrates the concentration of seats near the center of action. C. A. Neff, 


architect; C. J. Lindeman, engineer. 


DESIGN DETAILS 


Orientation of Athletic Fields 


A single misplay may mean the loss of an important 
game, and such a misplay may be caused by the glare of 
the sun’s rays in the player’s eyes. In planning an ath- 
letic field, therefore, one of the first considerations must 
be orientation of the various fields of play with respect 
to direction of the sun’s rays. Studies of ideal orienta- 
tion may determine the choice of the site for an athletic 
field where more than one site is under consideration 
and such studies are of value in locating the seating 
structures to best advantage. Other considerations may 
make it impossible to obtain ideal orientation but it is 
important to know what the ideal direction would be 
and adopt a layout as close to this as possible. 

The direction of play in football 1s generally in lines 
parallel to the long axis of the field. The football season 
is Short, usually October and November, and games are 
generally from about 2:00 to 4:00 in the afternoon, so 
that ideal orientation of football fields can be accurately 
determined. Main consideration should be for the play- 
ers as spectators welcome the sun’s rays at this time 
of year. 

For baseball, conditions are generally considered most 
desirable when the sun’s rays are parallel to the line 
joining first and third base. Two positions of the dia- 
mond will meet this requirement. The season for base- 
ball is longer and warmer than for football and for the 
professional leagues at least, the spectators are given 
more consideration in selecting the orientation. Specta- 
tors generally prefer to sit along the first base line with 
the sun at their backs. 

Maps have been published from which the ideal orien- 


10 


tation of football fields and baseball diamonds in any 
part of the United States can be determined easily*. 
These show that for the center of the time zones, the 
short axis of football fields should be at an angle of 
about 50 deg. east of true north. Similarly the line from 
first to third base of baseball diamonds should be at an 
angle of about 72 deg. east of true north for projects 
located near the center of the time zones. These angles 
increase toward the east and south of the center of each 
zone and decrease toward the west and north of the 
center by a maximum of about 8 deg. 


Sight Lines 


The principal purpose of a grandstand is to provide 
the public with a good view of the performance under 
comfortable circumstances. The view is affected both by 
the distance to the action and by any obstruction to the 
sight line. The sight line is the straight line between the 
observer's eye and the object. 

The center of action for football is at the center of 
the gridiron and that for baseball at the center of the 
diamond. In football it is particularly noticeable that 
with unreserved seats the patrons choose seats as near 
the center of action as possible. This results in the out- 
side edge of the crowd forming an approximate arc with 
the center on the 50-yd. line**.Several grandstands have 
been built with the back conforming roughly to this arc. 

Sight lines are generally considered only normal to 
*“The Orientation of Athletic Fields’ by Gavin Hadden, Ameri- 
can City, May, 1928, Vol. 38, No. 5, page 138. 


**“Tnfluence of Loci on Engineering Design” by Gavin Hadden, 
Cwil Engineering, December, 1934, Vol. 4, No. 12, page 632. 


the stand, the oblique lines to different parts of the field 
being neglected. Some stands, particularly large bowls, 
have been built with a curved front so that the normal 
line approaches the line to the center of action. The 
additional complexity and cost of design and construc- 
tion of such curved structures is not justified with small 
stands. 

For the best view, there should be no obstruction be- 
tween the spectator’s eye and any part of the field of 
action. This requires that the sight line to any part of 
the field should be above the spectators in front. It is 
commonly assumed that for a seated spectator the eye 
is 4 ft. above the floor and 6 in. below the top of his hat. 
Naturally these distances vary considerably with differ- 
ent individuals so that too great refinement in deter- 


Sight line diagrams. Dia- 
gram A shows a curved seat 
section with common focal | 


a reasonable height, it seems justifiable to assume that 
spectators will have a satisfactory view if they can look 
over the heads of those in the second row ahead of them. 
This can be done if a value of 3 in. is used for c. 

The focal point is the intersection of the sight line 
with the playing field or other object of interest. For 
football the focal point should be at about the nearest 
line of the playing field. For track, it should be at about 
chest height for a runner in the closest lane. For base- 
ball, it should be the catcher. If these points of interest 
are beyond the focal points for all seats computed on 
basis of c equal to 3 in. the view will be satisfactory, 
particularly since a large part of the action will occur at 
points where the computed value of ¢ will be larger. 

If the focal point for all seats is made the same, a sec- 


DIAGRAM A 


En 


of 


point. Diagram B shows 


dn 


AE 


straight seat section with vari- 
able focal points. The eleva- 
tion of front and rear seats and 
the sight line clearance are the 
same for the two diagrams. 


ian 
O =| 
IZ") 
Se 

Lege | eal ] 
ge a 
Pe | sell 
Sa ial + 
ee ge 
Se a a 

DiacRaAM B eee Lt 


mining sight lines is not warranted when the original 
assumptions at best can be only approximate. 

With a given focal point and elevation of the first 
seat, the required elevation of the other seats is ma- 
terially affected by the assumed value of ¢ (the clearance 
between successive sight lines). As previously stated, 
for unobstructed view the value of c should be 6 in., the 
assumed distance between eye and top of hat. However, 
except for small grandstands, this will frequently re- 
quire the rear seats to be at an excessively high eleva- 
tion. Many grandstands, in fact practically all large 
ones, have been built on the basis of a smaller value of c. 
While this smaller value has generally been dictated by 
the practical consideration of keeping the structure at 


tion through the seat deck will be a curve as shown in 
Diagram A. Diagram B shows the sight lines for a 
straight section in which the first and last seats and the 
clearance, c, are the same as in Diagram A. With this 
straight section, the focal point is different for each row 
but the average is approximately the same as the focal 
point for the ideal curved section. In other words, with 
the straight section the lower seats have better visi- 
bility and the upper seats poorer visibility than those 
in the curved section, but the average is the same. 
Since with a straight section the top seat has the poor- 
est view, it is necessary to check only this seat in order 
to determine that all seats are satisfactory. The relation 
between distance from seat to its focal point, d, height 


Il 


of the eye above focal point, e, width of tread, t, height 


of riser, r, and clearance, c, is represented by the simple 


d l 
formula Pare Betas: 


r—c 
For a curved section the relation of the various factors 
are represented by the formula 


&n = dp E ae ; (S.-81) | 


in which en=elevation above focal point of eye of 
spectator in row n. 
e; =elevation above focal point of eye of 
spectator in row 1. 
dn = distance from focal point to row n. 
d, = distance from focal point to row 1. 
c =clearance between successive sight lines. 
t = width of tread. 
S; and Sp, =values from table corresponding to 


" and * . For simplicity the value of d, 


should be an exact multiple of ¢. 


As an example of the use of this formula, assume that 
it is desired to design a grandstand with a common focal 
point but otherwise approximately the same as that 
shown on page 24. Assume the factors: e:=6 ft., di= 
32 ft., c=0.25 ft., t=2 ft. Then the formula becomes 


re hy 
aah, E bt "2 (Sy—3.3182) | 


which can be simplified to en=dn (0.125Sn—0.2273) for 
these specific conditions. For the last row dn=78; 
on 39; from the table, S,=4.2279; and the formula 
gives €n = 23.494 which is the distance above the focal 
point of eye of spectator in the last row. The elevation 
of the tread used by this spectator is then 23.49—4.0= 


19.49. The elevation of each row is obtained similarly. 


nia 


VALUES OF S 


d S d Ss d S 

i i i 

1 0.0000 36 4. 1468 ra 4. 8328 
2 1.0000 37 4.1746 72 4.8469 
3 1.5000 38 4.2016 1 4.8608 
4 1.8333 39 4.2279 7A, 4.8745 
5 2.0833 40 4.2535 73 4. 8880 
6 2eeGeos Al 4.2785 76 4.9014. 
7 2.4500 42 4.3029 [1 4.9145 
8 2.5929 43 4.3267 78 4.9275 
9 2.7179 4A 4.3500 79 4.9403 
10 2.8290 45 4.3727 80 4.9530 
1 2.9290 46 4.3949 81 4.9655 
12 30199 AT 4.4167 82 4.9778 
13 3.1032 48 4.4380 83 4.9900 
14 3.1801 49 4.4588 84 5.0021 
15 3 2516 50 4.4792 85 5.0140 
16 3.3182 51 44992 86 5 0257 
17 33807 52 4.5188 87 5.0374 
18 3 4396 53 4.5380 88 5.0489 
19 3.4951 54 4.5569 89 5.0602 
20 3 5477 Se 4.5754 90 5.0715 
21 3.5977 56 4.5936 91 5.0826 
29 3 6454 57 4.6115 92 5.0936 
23 36908 58 4.6290 93 5.1044 
24 3.7343 59 4. 6463 904 5.1152 
25 3.7760 60 4. 6632 95 5.1258 
26 3.8160 61 4.6799 96 5 1263 
27 3 8544 62 4.6963 97 5.1468 
28 3.8915 63 4.7124 98 5.1571 
29 3.9272 64 4.7283 99 5.1673 
30 3.9617 65- 4.7439 100 5.1774 
31 3.9950 66 4.7593 101 5.1874 
32 4.0272 67 4.7744 102 5.1973 
33 4.0585 68 4.7894 103 5.2071 
34 4. 0888 69 4.8041 104 5.2168 
35 4.1182 70 4.8186 105 5.2264 


*Modification of formula given by A. B. Randall and E. S. Crawley, 
“The Design of Seating Areas for Visibility”, American Archi- 
tect, May 21, 1924, Vol. 125, No. 2446, page 487. 


An interesting effect is obtained by the shadows on the 
many planes on the rear of the Walter Strong Memorial 
Stadium, Beloit College, Beloit, Wis. The seats are con- 
centrated near the center of the field. Allen & Webster, 
architects; Mogens Ipsen, engineer. 


The popularity of football is shown in this view of the stadium at Northwestern University, Evanston, Ill. Even the tem- 
porary stands at the ends of the field are filled. The crescent shape and balcony concentrate the permanent seats near the 
center of the field. The cross section of the seat deck is curved by using variable riser heights to provide equal sight lines 
for all seats. Original plans call for increasing the capacity of this structure as funds and demands warrant by ulti- 
mately providing two balconies on each side of the field. James G. Rogers, architect; Gavin Hadden, engineer. 


To provide this curved seating section requires that 
each riser be slightly higher than the preceding one. 
Few grandstands have been built to the theoretical curve 
but a number have been constructed with a series of 
straight sections which approximate the theoretical 
curve. This is obtained by increasing the height of riser 
for succeeding groups of 5 to 10 rows rather than for 
each row. This greatly reduces the construction difficul- 
ties involved in the use of variable riser heights. Such 
a plan is recommended for structures containing more 
than about 25 rows of seats and may be used in smaller 
structures. 


Treads and Risers 


The seat treads and risers should be as small as pos- 
sible for the sake of economy, but must be sufficient 
for comfort and a good view. Increasing the width of 
tread will, of course, increase comfort by providing more 
leg room, but it will also reduce the sight line clearance. 

Most grandstands have a tread of from 24 to 30 in. 
A width of 25 or 26 in. gives reasonable comfort and 
economy and is probably most satisfactory for the aver- 
age case. Twenty-four inches should be the minimum 
considered although a very few structures have been 
built with narrower treads. Where cost is not particu- 
larly important, the treads may be as much as 30 in. 
Where there is much movement of the spectators during 
the program, as at race tracks, the treads must be 
wider than when the spectators remain at their seats 
from the beginning to the end of the program, as at 
football games. More room per seat is also generally 
provided for baseball games than for football games. 
(See page 15 for tread width where seats with backs 
are used.) 

The height of the riser affects the cost and sight lines. 


Increasing the riser height will increase the total height 
of the structure and consequently its cost. The sight 
lines are controlled by the ratio of riser to tread, the 
sight clearance, and the location of the first seat in rela- 
tion to the assumed focal point. This is shown by the 
diagrams and discussion on page 11. Ordinarily the height 
of riser is the least fixed of these dimensions and varies 
from 6 to 18 in. However, most of the small stands have 
risers between 9 and 14 in. The elevation of the first 
seat should not be any higher than necessary since extra 
height means extra cost and poorer sight lines. 

The first tread should be wide enough to provide 18 
in. between the front edge of the seat and the wall or 
rail. Additional width is not necessary unless a definite 
cross aisle is required. The distance between the back 
of the last seat and the rear wall need not be more 
than 6 in. 


Seats and Seat Supports 


The space allowed for each seat, lengthwise of the 
row, is generally between 17 and 1814 in. The 17-in. 
width should be the absolute minimum and a width 
of 18 in., which is required by many building codes, 
is preferable. Even in the same section, the width of 
seats may be varied slightly to provide for varying 
total length of rows caused by entranceways, aisles, 
etc. The height from deck to top of seat should be 
approximately 18 in. 

The seats themselves are usually of wood, nominally 
2 in. thick and 8 to 12 in. wide, preferably a minimum 
of 10 in. The width may be made up of one, two or three 
pieces, fastened to supports attached to the deck. Seats 
made up of two or three pieces are recommended since 
they have less tendency to warp than those made of a 
single plank. Although many seats are made level, greater 


13 


Treated 


A" thick 
treated 
wood 


Typical seats and seat supports. Various other combinations 
or modifications of these typical details may be made to suit 
personal ideas. Seats may be fastened to supports by bolts or 
screws, and bolts cast in the concrete or expansion bolts may be 


comfort and better drainage are provided by tilting the 
seat slightly, making the front edge 14 to 1 in. higher 
than the back edge. 

Douglas fir, redwood and Southern cypress are most 
commonly used. While No. 1 grade common lumber has 
given good results, the better grades are generally used. 


le, 


welded 


used to fasten the seat supports to the concrete. The first two 
supports are applicable only to relatively high risers, but the 
others may be used with any height of risers. 


The boards should be free of pitch and should be kiln- 
dried or air-seasoned before using. Lumber may be 
treated with preservatives to prolong its life and may 
be painted for further protection and to reduce the 
tendency of the upper surface to cup. Protective mate- 
rials and paints should be selected and applied so that 


The popularity of playgrounds is increased whenever small, inexpensive bleachers are provided. 


Hampton St. Playground, Holyoke, Mass. A small base- 
ball grandstand with largest number of seats near the 
home plate. Paul S. Howes, architect; Philip E. Bond, 
engineer. 


Morgan Park, New London, Conn. Riser bents were pre- 
cast, other members cast in place. George A. Waters and 
K. H. Holmes, engineers. 


14 


Phillips High School, Birmingham, Ala. Precast concrete 
slabs 4 in. x 16 in. x 5 ft. long were set in the embankment 
to provide supports for the seats and hold embankment in 
place. This economical scheme for playground seating is 
applicable only in mild climates. J. D. Webb, engineer. 


Ansonia, Conn. Wood plank seats are supported directly 
on reinforced concrete stringers. V. B. Clark, engineer. 


Simple masses of concrete with texture produced by form boards distinguish the baseball grandstand at Seattle, Wash. 
William Aitken, architect. 


staining of clothing will not occur. Top edges of seat 
boards should be chamfered or rounded to reduce 
wear and splintering and to give better drainage. Con- 
tact areas between wood members should be avoided 
wherever possible to reduce deterioration. 

Various designs of seat supports have been used, some 
attached to the risers and others attached to the treads 
of the seat deck. A few examples of these seat supports 
are illustrated. In making a selection, consideration 
should be given to the ease with which the support can 
be placed in proper position, its interference with clean- 
ing the structure and the opportunity for drainage of 
moisture away from the metal and wood parts to reduce 
deterioration. Supports attached to the riser have advan- 
tages in these respects. On the other hand some of those 
placed on the tread are lower in first cost. To reduce 
breakage of the wood seats, the bracket should give 
practically complete support across the width of the 
seat. Supports are placed at about 4-ft. intervals along 
the length of the seats. The ends of planks may meet 
over a support, or two supports about 1 ft. apart may 
be used. Seats should stop or be cut at expansion joints 
with a support used close to each side of the joint. Where 
the seat extends less than 4 ft. beyond the joint, the 
plank may be continuous if not rigidly attached to the 
end support. Fastening devices driven from the under- 
side of the seat and extending only part way through 


the wood will reduce the decay hazard. Through bolts 
are stronger but increase the decay hazard due to the 
retention of moisture. 

Grandstands for professional baseball games and horse 
races are generally equipped with seats having arms 
and backs. These require more space than the bleacher 
type of seats, the exact requirements depending upon 
the type of seat. Manufacturers of such seating equip- 
ment should be consulted. For these individual seats a 
tread of 32 in. (36 to 39 in. for race tracks) and a seat 
width of 19 or 20 in. are common. Attaching the seats 
to the risers rather than the treads is advantageous with 
these seats as well as with the bleacher type. The num- 
ber of seats between aisles should be reduced from that 
given in the next paragraph. Fixed seats in boxes re- 
duce maintenance. 


Aisles 


Grandstands are generally divided into sections by 
transverse aisles. The sections usually have from 24 to 
32 seats per row between aisles. The most favored width 
appears to be either 26 or 28 seats. 

Aisles beside the end walls are sometimes advan- 
tageous where they can be connected directly to an 
entrance but are not essential. The width of one aisle 


art T T T T 
iq 25 —— Expansion joints 


= Se Expansion fo f: = eee Expansion _joints —~—, 
(ee eee SS a 

—S— ——S—S=[=—=—=ap==—— 
a _————e 
=== = =SSS==S=S===S=E_]-]|== 
SS ——SSSSSS=—S=sssS> 
—=S=— 
—— SSS 5S SS 

ESS Se 
— SS eS = 


A 


Alternate arrangement of aisles and entrances for 2100-seat 
grandstands shown on page 24. The solid line at the top shows loca- 
tion of column bents with reference to expansion joints. Note increase 
in aisle width toward exit. The capacity may be increased in the orig- 
inal construction or at a later date by using additional sections. In 


Diagram A, all sections are the same. In Diagrams B and C, the center 
and right hand sections are typical except that instead of the ramp 
for the right hand section in C, temporary steps are used until the 
next section is added. The left hand sections of B and C are modified 
by the use of an extra aisle and special entrance. 


15 


Main entrances to the Suffolk Downs Race Track grandstand at East Boston, Mass., are characterized by open cantilever 
design of stairways. Note division rails on wide stairs. Mark Linenthal, engineer; Blackall, Clapp, Whittemore & Clark, 


associate architects. 


can be saved by placing the first aisle one-half section 
from the wall. 


Widths of aisles vary, but the most common width is 
3 ft. This width permits a single file in one direction and 
an usher going in the opposite direction. In a few cases 
aisles are 4 ft. wide, permitting two lanes of traffic in 
the same or in opposite directions. Where there are 
aisles on both sides of an entranceway, they may be 
only 2 ft. wide. These widths are considered the mini- 
mum advisable to insure sufficient clearance against 
hazard of clothing catching in the seats or disturbing 
the occupants of the end seats. Where seat risers are 
more than 9 in. high, an extra step in the aisle is pro- 
vided for each seat riser, making each step riser one- 
half the height of seat riser and each step tread one-half 
the width of seat tread. Steps should be the full width 
of aisle. 


Longitudinal aisles, whether placed in front of the 
first row of seats or part way up the stand, are objec- 
tionable as the view of spectators back of the aisle may 
be obstructed. However, where seats are not reserved 
an aisle at the entrance level will be a considerable 
convenience to the spectators in choosing their seats, 
but will interfere with the view of those already seated 
above the aisle. If the aisle is part way up the stand, 
the sight lines for the first few rows above it should 
be investigated for the effect of the extra aisle width. 


16 


Entrances and Exits 


In the small stands without entrance through vomi- 
tories it is preferable to have entrances from the field 
level at each transverse aisle rather than simply 
entrances at each end with a longitudinal aisle leading 
to the transverse aisles. With a small grandstand built 
on an embankment, entrance can frequently be made 
at the rear directly to each aisle or to a longitudinal 
aisle or concourse connected with the transverse aisles. 

In the larger grandstands, entrance is made through 
vomitories. The favored width of vomitory is 6 ft., 
although many are 8 ft. and some are only 4 ft. Stand- 
ard requirements for exits are based on traffic lanes of 
22-in. width. Widths of vomitories and passageways 
should, therefore, be in approximate multiples of this 
width. Handrails extending not more than 31% in. from 
the wall are not considered as reducing the effective 
width of passageway. 

Most building codes specify width of exits in terms 
of number of seats. For example, if 8 in. is required 
for each 100 seats, a single vomitory or gate serving 
a section of 800 seats would require a width of 64 in. 
However, this should be increased to 66 in. to provide 
three 22-in. traffic lanes. 

Where the seats do not have back rests, many of 
the patrons will approach the exits by walking over 
the seats rather than in the aisles. In such cases it 


is not necessary to have the width of aisles equal to 
the width of exits, in fact the code requiring the width 
of exits to be 8 in. per 100 seats permits the aisles to 
be 6 in. per 100 seats. 

The location of vomitories will depend upon the con- 
tour of the site and the size of the section served. Where 
the section served is relatively small, the vomitory can 
be at the same level as the entrance, thus avoiding ramps 
or stairs. For larger sections it is advisable to place the 
vomitory part way up the stand so that it will be served 
by an aisle below as well as the aisle above. In the very 
large stadiums, a second row of vomitories is provided 
to serve the upper sections of the stand. 


Stairways and Ramps 


Various studies have been made of the rate of egress 
from stairways and ramps. Some of these indicate aver- 
age values of about 30 persons per minute per traffic 
lane of 22-in. width for stairways and about 37 for 
ramps. Some authorities give higher values, in some 
cases assuming a rate of egress of 45 persons per minute 
per traffic lane for both stairways and ramps. On this 
basis, and assuming that it is desired to exit the entire 
crowd in 5 minutes, a grandstand seating 10,000 persons 
will require a total of 45 lane widths of exit ramps, vomi- 


oA ) ae \ wes @ 


wa: aE Bs rn 
uoUgE 
eormnrmner rasa yal 
1 wo 
s 
vy 


DONDE &e 
SETTGUTING Og aAS 


This municipal stadium at Ports- 
mouth, Va., has a gracefully curved 
cantilever roof of reinforced con- 
crete covering a portion of the 
grandstand. Individual seats are 
provided in the center section and 
the usual bleacher type for the re- 
mainder of the stand. Rudolph, 
Cooke and Van Leeuwen, Ine., 
architects. 


aT. NUVI WNDU ODUY 
AOR NR 


hen ae ! 
ee eral ah joints —— 


Arrangement of aisles at vomitories. Aisles should be ar- 
ranged not only to handle the crowds efficiently but to fit the 
location of the expansion joints, shown by light double lines. 
With the arrangements of expansion joints shown, the walls around 
the vomitories are carried on the deck and the ramps or stairs 
are self-supporting and free from remainder of the structure. 


tories, stairways or gates directly from 
the seat deck. This total width must be 
maintained all the way to the outside of 
the grandstand and enclosure. 

In designing stairways, certain rules 
are widely used. These require that the 
sum of riser height and tread width, in 
inches, shall not be less than 171 nor 
more than 18; that the sum of 2 risers 
and 1 tread, in inches, shall not be less 
than 24 nor more than 25; that the 
product of riser and tread, in inches, 
shall fall between 70 and 75. Risers of 
61% to 71% in. with treads of 11 to 10 
in. are most commonly used and con- 
form to these rules. 

Ramps are frequently used, instead 
: of stairs, from ground level to the vomi- 
tory. Their capacity to handle crowds 


tt nn 
BUNT PL 


ct. ries 


Rail and flag pole anchorage. 
Rail or pole anchorage should be 
of a type which will securely fasten 
the rail or pole to the structure but 
will not cause the concrete to crack 
or accelerate rusting. Large pipe 
embedded directly in the concrete, 
particularly in thin walls, so reduce 
the section of concrete that cracks 
are likely to occur. Sketch A shows 
a short spiral or reinforcing bars 
inserted to compensate for the con- 
crete displaced by the pipe. Using 
the small pipe as a dowel rather 
than a large pipe as a socket, also 
reduces the tendency to crack the 
concrete and rust the pipe. Sketches 
B, C and D show the most com- 
mon types of standard fittings for 
railings. Side fastenings such as D through H, where they can 
be used, have the advantage of increasing the effective width of 
stairs or passageway and allow water to quickly drain away from 
the metal. Types E and F are satisfactory for small and medium 
size flag poles as well as railings. Type I may be used for anchor- 


Spiral 
4°6-2"pitch 


is between that of stairways and level passageways, 
but they are recommended primarily for greater 
safety rather than for greater capacity. Requirements 
for building exits often limit ramp slopes to not more 
than | in 10 because of the danger of possible panic from 
fire or other cause, but since this is less in grandstands 
than in buildings, somewhat steeper slopes can be used. 
Ramps as steep as | in 4 have been used, although 
slopes of 1 in 6 to 8 are safer and more commonly used. 
Ramps are longer than stairways of the same height. 
They are particularly suitable for grandstands where it 
is not necessary to make maximum use of the space 
under the deck and in the very large stadiums of con- 
siderable height. 


Walls and Railings 


Protection at front, back and sides of the grandstand 
and around entrances may consist of solid walls of con- 


18 


ing base plates for medium or large flag poles or floodlight poles. 
The details shown of the base itself are not significant. The spe- 
cial stresses caused by wind on medium or large poles must be 
considered in the design of the supporting structure as well as 
the fastenings. 


crete or of pipe sections anchored to the concrete. Solid 
walls in front of the first row are not more than 3 ft. 
high above the lower tread. A height of 32 in. above the 
lip of the step is quite often used for handrails on 
enclosed stairways. For greater safety, rails and walls 
at ends of stands and around entrances are usually 3 to 
3% ft. above the front edge of the tread. Solid back 
walls give spectators protection against strong winds 
and are therefore frequently made higher. 


Fences and Entrances 


Where admission is to be charged, a fence to enclose 
the field is necessary. While wire fences have been used 
on some projects, they do not shut off the view of people 
on the outside. Many of these spectators would prob- 
ably pay admission if a solid fence enclosed the field. 
Those who have paid admissions do not like to know 
that others are able to view the events without payment. 

Attractive fences of concrete, designed and built to 


Concyete fences are widely 
used to enclose athletic fields. 
They harmonize with the 
grandstand and are an effec- 
tive screen. The ticket offices 
and entrance gates form an 
integral part of the fence and 
entrance detail at Lane Tech- 
nical High School, Chicago. 
John C. Christensen, archi- 
tect, Chicago School Board. 


Entrances to the playing field may be of concrete to match the grandstand as at the John Fawcett Stadium, Canton, Ohio. 
Ticket offices have been incorporated in the entrance. Charles E. Firestone, architect and engineer. 


harmonize with the grandstand structure, can be used to 
cut off the view from the outside. The concrete may be 
cast in place, precast in special large units, or the usual 
concrete masonry may be used. Decorative treatment 
can be given to the fence, and the texture suited to the 
design. In some cases an ornamental entrance to the 
playing field is provided. Such an entrance may be com- 
bined with the enclosure fence and treated as a separate 
structure, or it may be an integral part of the grand- 
stand structure. Ticket booths may be incorporated in 
the entrance. 

Gates in entrances, fences or enclosure walls should be 
so arranged that a single file of the crowd going in passes 
each ticket collector. However, to provide quick, unob- 
structed passage for exit of the crowd, it should be pos- 
sible to throw the gates wide open. The accompanying 
illustrations show a few entrances and fences as ex- 
amples of the suitability of concrete for these structures. 


Illumination for Night Play 


Baseball, softball and football played at night are at- 
tracting large crowds of spectators. A high level of 
illumination is required, so distributed that the field and 
the ball as it flies through the air can be seen clearly from 
all positions. Requirements of spectators as well as 
players must be considered. The minimum illumination 
will depend on the game to be played; the class of event, 
that is, whether major or minor league, professional or 
amateur; and size of audience. As the number of spec- 
tators increases the illumination must be increased as 
the farthest-away spectators have to see from a greater 
distance. 

The best results are secured with modern, efficient 


floodlights used in accordance with sound principles of 
lighting as recommended by the National Electrical 
Manufacturers Association*. Engineers thoroughly fa- 
miliar with these requirements and experienced in this 
work should be engaged to plan the installation. 
Groups of floodlights are placed on poles or towers. 
For covered grandstands, all or part of the lights can be 
placed on the roof if this is designed to carry the extra 
load. Light poles in front of the grandstand interfere 
with the view of the spectators. Placing them farther 
back requires only a few additional lamps and little 
additional power, generally not more than about 5 per 
cent additional. The lamps, however, must be placed 
higher as the distance from the field increases. For 
example, the recommended height for poles set 20 ft. 
from the sidelines of a standard football field is 45 ft., 
and a height of 95 ft. is recommended where they are set 
120 ft. from the sidelines, with heights in direct propor- 
tion for intermediate positions. To compensate for the 
greater height of poles, fewer of them are necessary. 
When the lights are placed at distances of 30 ft. or less 
from the sidelines of football fields, 5 poles are usually 
required on each side of the field. When placed 75 ft. or 
more from sidelines, only 3 poles are required on each side. 
In some of the newer grandstands suitable bases are 
provided at the upper edge of the deck on which towers 
are erected for mounting the floodlights. Thus good 
lighting is provided without obstructing the view of any 
spectator, and at the same time the lighting facilities are 
made an integral and harmonious part of the structure. 


*Standards for Floodlight Distribution Curve and Layout for Outdoor 
Sports issued by National Electrical Manufacturers Association, 
155 East 44th St., New York, N.Y. 


19 


The ornamental concrete fence harmonizes with and unites the two stands of the high school stadium at Dallas, Texas. 
The roof of the broadcasting booths, located above a spacious press box, is used by cameramen. The floodlights are sup- 
ported on the rear of the structure so as not to interfere with the view of the spectators. Hoke Smith, architect; R. L. 


Rolfe, engineer. 


FACILITIES 


Most grandstand projects involve a number of facili- 
ties or accommodations for spectators and participants 
in addition to the provisions for seating. Such facilities 
will vary with the size of project, money available and 
other factors. Some of the major items that should be 
considered for every project, except possibly the small- 
est, are discussed below. 


Dressing and Locker Rooms 


In grandstands used for athletic events, suitable dress- 
ing rooms should be provided for both the home and 


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Fes ee es ae ee ao ea 


: 


visiting teams. Visiting teams may use the same facili- 
ties ordinarily used by the second, freshman or girls’ 
teams. Each team room should have at least 2 water 
closets, 4 urinals and 2 wash basins. Where accommo- 
dations are not provided in adjacent buildings, the team 
rooms should have showers, lockers. benches, chairs and 
rubbing tables. 

In addition to the desired number of lockers, the 
locker room must have sufficient benches and open area 
so that the players can change clothes without too much 
crowding. In grandstands, the locker room generally 


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1820" 6-6" 


oO" 


Facilities under a 2100-seat grandstand. 


20 


Dugouts 


Frequently the only seating facilities for players dur- 
ing a game are portable benches placed against the front 
of the grandstand or somewhere between the grandstand 
and the playing field. It is much better practice to pro- 
vide fixed seats in dugouts. Placing the floor of the 
dugout below the ground level reduces the interference 
with the spectators’ view and gives some protection 
from the cold for the players. A roof gives additional 
desirable protection. To give the players a good view 
of the game, the elevation of the floor should be as high 
as possible without interfering with the spectators’ view. 
This will also make drainage easier. 

The dugout should be long enough to provide seats 


FOO. V2.9 OV ager, 040” 


4"concrete bracket support I 


Floor drain | 
3"C. 1 pipe - connect to /7 
concrete pipe drain 


HATES 


Sleytr a 
Obs. 8: 


has Pen cerains eS RL OES 5 
230-26. Slashes! 


Floor drain 


| | 
3"C.1. pipe-connect to /7 ! 
concrete pipe drain vA 


Dugout and players’ box. The dugout or players’ box should be long enough to accommodate the entire squad of players. Drainage 


must be provided. 


contains 10 to 25 sq.ft. per locker. Where the smaller 
values are used, the lockers must be well distributed 
over the entire area of the room. If the locker rooms 
are to be used for general physical education classes 
the rule applying to gymnasiums should be considered. 
Under this rule the area of the locker room is deter- 
mined on the basis of 32 sq.ft. for each person using 
the locker room at any one time, or on the basis of 
8 sq.ft. for each of the total number of lockers. The 
larger of the two areas thus determined must be used. 
In some cases the lockers are artificially ventilated by 
connecting them to intake and exhaust ducts. Such ven- 
tilation is particularly desirable where players’ suits and 
equipment are to be left in the lockers. 

In estimating the number of showers, itmay be assumed 
that each shower will serve 5 persons. About 25 sq.ft. 
should be allowed for each shower. 

Showers have been omitted at some of the smaller 
high school grandstands, even where the athletic field 
is located some distance from the school building. Buses 
or automobiles are used to transport the teams to and 
from the athletic field, so that shower and dressing 
facilities at the school building can be used. Even with 
this arrangement rest rooms with toilets are essential 
at the grandstand for the players. 

In most sections of the country, it is necessary to 
heat the dressing rooms. This may be done from a 
central plant or a local installation. Gas-steam radiators 
are often used. Facilities for heating water for showers 
are also necessary. 


for the entire squad of players. In addition to the seats, 
a drinking fountain, permanent or movable, and tele- 
phone connections to the press box and scoreboard are 
desirable. 

Where it is impossible to place the dugout adjacent 
to the front of the stand because of the running track 
or entrance to the stands directly from the field, the 
players’ box, shown above, may be placed closer to 
the sidelines. For such locations the lowering of the 
players’ heads is particularly advantageous for the spec- 
tators’ view. 


Detail showing concrete roof over dugout at Michigan State 
Normal College grandstand, Ypsilanti, Michigan. Giffels & 
Vallet, Inc., architects and engineers; L. Rossetti, associate. 


21 


Space under the grandstand at West Carrollton, Ohio, is used for 
the storage of school buses. Simple ornament cast in the concrete 
by the use of molds in the forms adds to the attractiveness. The 
toilet fixtures are vented through the cross-fitting on the flag pole. 
Rial T. Parrish, architect and engineer. 


Public Facilities 


Public toilets should be provided in practically all 
cases. One authority estimates that the following fix- 
tures are required: for each 1,000 men, 1 water closet 
and 6 urinals; for each 1,000 women, 7 water closets. 
In some locations, building codes require public toilets 
and specify minimum requirements. For example, one 
city requires for the women’s toilets, | water closet for 
each 800 seats, and for the men’s toilets, 1 water closet 
for each 675 seats, and 1 urinal for each 200 seats. These 
requirements are for baseball and other athletic grand- 
stands. For larger stadiums to be used for a variety of 
purposes the same code requires for the women’s toilets, 
1 water closet for each 600 seats, and for the men’s 
toilets, 1 water closet for each 750 seats and 1 urinal 
for each 225 seats. The same code requires at least 1 
lavatory in each toilet room. It also makes mandatory 
the installation of drinking fountains, at least 1 for each 
2,000 spectators. The fountains are not to be placed 
in toilet rooms and are to be so located that the hori- 
zontal distance to be traveled by any spectator in reach- 
ing them shall not exceed 400 ft. In the large grand- 
stands several toilet rooms should be provided to make 
them easily accessible. All toilet rooms should be well 
lighted and ventilated and designed for easy cleaning. 


Hollow concrete units form the en- 
closure of this concession space under 
the grandstand at Mooseheart, IL. The 
cast-in-place concrete lintel has a 
simple and inexpensive decorative 
treatment. The plaques are of cast 
stone. 


ops 


Concessions 


Booths for refreshments and other concessions are 
often the source of extra income at well patronized 
grandstands besides being conveniences appreciated by 
the public. They are often of a temporary nature, espe- 
cially at football grandstands, consisting of wood coun- 
ters placed between columns under the deck. Portable 
equipment furnished by the concessionaire is usually 
used, but electrical outlets and waste sink with drain 
as well as a water supply should be provided. A small 
storage room in back of the booth is sometimes pro- 
vided. In grandstands that are used more frequently, 
such as the professional baseball grandstands, more per- 
manent construction should be provided and sufficient 
space allowed for servicing the vendors of refreshments 
who distribute these throughout the stand. 


Ticket Booths 


Ticket offices or booths are usually placed at or near 
the main entrances. They should be so placed that they 
are convenient but do not interfere with the entry of 
those holding tickets purchased in advance. A booth 
for one ticket cashier may be as small as 3 ft. square. 


Offices and Storage 


Space under the grandstand can be used for offices 
of the operating management, the athletic departments 
of schools, or for other purposes. Closed-in storage rooms 
for athletic equipment, janitor’s materials and ground- 
keeping equipment are often desirable. The sizes of these 
rooms will, of course, depend on how they are to be 
used, but are generally determined by the space remain- 
ing after providing adequately for the more important 
facilities previously discussed. 


Press and Broadcasting Accommodations 


Schools and colleges have come to realize the great 
value of favorable publicity and friendly relations with 
the public. Commercialized sports, such as professional 
baseball and football, have appreciated this for a long 
time and make adequate provision for representatives 
of the press and for radio broadcasting. Suitable pro- 
visions for these services have been neglected in many 
instances, or have been added after the main structure 


was erected, sometimes resulting in more or less make- 
shift accommodations out of harmony with the rest of 
the structure. Provision for these accommodations 
should be made in the original design, and the construc- 
tion should be permanent and fit into the general scheme. 
The space should be covered and preferably enclosed 
with movable plate glass windows on the front. Double 
glazed windows hinged at the top to swing outward are 
recommended. 

For football grandstands these facilities should be 
centered on the 50-yd. line and are generally at the 
top of the stand. They should be so elevated that the 
reporters’ view will not be obstructed by a standing 
crowd. For baseball grandstands these facilities should 
be located near home plate. If the stand is roofed, the 
press box may be suspended from the roof near its front 
edge, otherwise it should be at the rear. 

The space and equipment for reporters and broad- 
casters will depend upon local conditions such as the 
importance of the contemplated events and the number 
of press representatives and broadcasters expected. 

The minimum facilities should be a continuous desk 
about 18 in. wide with an allowance of 2 lin.ft. per man. 
Where a wire report is being sent, the reporter and his 
telegrapher will need at least 4 lin.ft. of desk as well 
as proper telegraphic connections. Some representatives 
telephone their reports to their offices either during or 
immediately after the game, so consideration should be 
given to furnishing the necessary facilities. Telephone 
connections with the players’ bench and scoreboard are 
also desirable. Electric lights should be provided and 
some form of heating is desirable. 

The size and equipment of broadcasting booths will 
also vary with the importance of the contest and the 
size of staff. Generally accommodations should be pro- 
vided for 2 engineers with their equipment and the 


Press box seating. This simple arrangement of facilities on stand- 
ard treads and risers can be added to existing structures or used 
on new stands without changing the regular construction of the 
seat deck. The table is fastened to the deck with the standard 
seat support attachments. An enclosure or at least a roof should 
be provided. 


announcer with 2 or more assistants. This requires a 
minimum room about 10 ft. long and 8 ft. deep. The 
furnishings should consist of a table across the entire 
front for the announcer and his assistants, another table 
about 3 ft. square for the engineers, and 6 or more 
chairs. Where the broadcasting will be done by only a 
small local station, the personnel may be less and the 
booth proportionately smaller. The booth should be 
soundproofed to prevent interference from outside noises 


The press box of architectural concrete is an integral part 
of the grandstand at Coatesville, Pa. The wide windows 
provide a good view of the playing field and there are few 
seats having an obstructed view. Lawrie & Green, architects 
and engineers. 


and the inside should be acoustically treated. Adequate 
ventilation must be provided. 

One very important item to be considered is the ade- 
quacy and location of electric, telephone and radio lines. 
There should be several electric outlet receptacles for 
power and heat as well as the electric lights. In addition 
to the outside telephone and telegraph connections, 
there should be lines to the players’ bench, scoreboard, 
and other points from which special items of interest 
may be broadcast. The lines should be in lead cables 
in weatherproof conduit. To prevent interference the 
cables for radio, telephone and power lines should be in 
separate conduits. 

Because of variations in equipment and local condi- 
tions officials of the broadcasting, press, telephone and 
telegraph organizations who are expected to use these 
facilities should be consulted regarding the exact layout 
and equipment. 


Public Address System 


A public address system is desirable for announce- 
ments during the progress of a game and particularly 
for entertainments in which there is speaking or singing. 
Permanent lines should be installed from the loud 
speakers to convenient outlets near points of interest 
on the field and in the press box or broadcasting booth. 


23 


STRUCTURAL DETAILS 


Loads 


Grandstands are ordinarily required to be designed 
for a live load of 100 lb. per sq.ft. of horizontal projec- 
tion. Investigations have shown that the mass and rigid- 
ity of reinforced concrete grandstands are such that 
stresses due to impact and wind load may safely be 
neglected in single deck structures. 


Framing 


With very few exceptions, grandstands are designed 
as a series of transverse bents supporting the seat deck. 
The bents consist of a sloping girder supported by col- 
umns on the necessary footings. Where the height of 
columns exceeds about 15 ft., it is usually desirable to 
use cross struts to reduce the unstayed height and to 
generally stiffen the bent. The selection of the size and 
reinforcing of these struts is primarily a question of 
engineering judgment rather than of analysis. The bars 


should extend through or be hooked into the columns. 
Although the stiffness may be increased by using fillets 
or haunches at the juncture of columns, girders and 
struts, the additional expense is not ordinarily justified 
except where such members intersect at an acute angle. 
The bents are held together longitudinally by the seat 
deck. Longitudinal struts, similar to those in the bents, 
should be provided to reduce unstayed column heights 
and add rigidity. 

The deck is designed with the riser acting as a beam 
between the sloping girders and the tread as a slab 
spanning between risers. In most instances the under- 
side of the deck is stepped the same as the top although 
a few stands have been built in which the underside of 
the deck is a plane surface. 

In designing the risers consideration should be given 
to using continuous straight bars in both top and bot- 
tom. This will require slightly more steel than where 
trussed bars are used but the unit steel cost will be 


SECTION B-B 


Pitch 3"in 2:0" 
ze Sa ee Oro ae eg eggs 
Citra gad nye apa 


Ri PRRRONS 


Bh) Sup 


Center line 
of girder 


eh : 3 * r a a 
>— = Press box = 
= - Saw 1 ; 
oes = ; 
9 =. = 
— 
— —-- 
ay 
gay | Se 
: s { Expansion =e 
eS fe ss J 
eee : =| 3 
-—— 
= E at = al rw) 
= -—o ys 
oO L— __ 
— + | | 
|_— SNe We 
= +— |} 2 i { a 
° im Ie et \— 
io} | ts) |e =| 
pire =a \5 =e 
= Expansion joints a BN : 
yet == 2 — ° ——+| - ° 2" Pitch ——- 9 =— 
! Lo" ; Gate =] = = iY 
| 6G 18-0 18-0" ako. 18-0" 18°0 a 13-0 i 18-0" ab 18-0" lee 
Column centers 14T'-O | 


SECTION A-A 


Seats on 


each riser prs 
=e 
a 


19-11" 


: 0" | 180" 
Ii = e SRamp wal | footing L_ aed 


Cross SECTION 


Typical design for 2100-seat grandstand. The capacity may be increased by adding sections, each seating 700. 


24 


less, construction will be simplified, and the steel will 
be more effective in reducing cracking due to volume 
change. The splicing should be at the center of span 
for the top bars and at the support for the bottom bars. 
The spacing of columns and bents will depend upon 
local conditions such as total width and length of stand, 
use of space under the stand, location of entrances, 
architectural treatment and minimum practical size of 
members. Generally the spacing is about 16 to 20 ft. 
Some economy may be obtained by making end spans 
slightly shorter or using a short cantilever end span. 


Expansion Joints 


Grandstands should be divided into convenient lengths 
to allow for the movement caused by changes in temper- 
ature and moisture content. The proper location and 
spacing of expansion joints must be determined for each 
job and since there are no fixed rules for this determina- 
tion some general comments will be helpful. Expansion 
joints should be placed where there is the greatest ten- 
dency for the structure to crack, such as where the 
section is reduced at vomitories and other openings. 


protect the drainage system from debris, a small catch 
basin type of fixture should be provided at the bottom 
of the trough. These fixtures should have handholes so 
that they can be cleaned easily. 


Probably the most common method of making an 
expansion joint watertight is to provide a crimped cop- 
per dam across the joint with an elastic material above 
and sometimes below it. In constructing such joints, 
particularly where the joint is sloped as in seat decks, 
it is important that the crimped portion not be filled 
or blocked by concrete or joint filler. With this space 
open, any water which passes the joint filler will be 
caught by the dam which will act as a trough to dis- 
charge the water at the bottom. However, if this trough 
is blocked by concrete or joint filler, a considerable 
head of water may develop above the stoppage and 
leaks occur. 

Waterstops or dams are usually made of 16 oz. copper. 
One-half-inch diameter holes at 8-in. centers punched 
near the edges of the strip will aid in securely anchoring 
it in the concrete. The dam must be so placed that the 
concrete will embed it securely. 


These joints are ordinarily spaced about 
60 ft. apart. 

Expansion joints must be made so 
that movement in them can easily take 
place. Joints in which there is friction 
between the moving parts have not 
proved entirely satisfactory and are not 
recommended. 

Completely open joints are prefer- 
able where leakage through the joints 
will not interfere with use of the space 
under the stand. The best location of 
these is between cantilever spans. Here 
it is advisable to finish the seat deck 
with small edge beams, the undersides 
of which form a plane surface. This con- 
struction prevents any water that comes 
through the joint from running back 
along the underside of the seat deck, 
thus causing discoloration and possibly 
more serious trouble. With these joints, 
the deck can be made watertight either 
when originally built or at a later time 
by fastening a trough tightly against 
the edge beams either by bolts cast in 
the concrete or by expansion bolts. 
These troughs should be connected at 
the bottom to a drainage system. To 


The Seattle High School Memorial 
Stadium, Seattle, Wash., consists of 
two similar stands both built for fu- 
ture extension at the ends. The roof, 
entirely of reinforced concrete, con- 
sists of a 314-in. slab supported by 8- 
in. thick ribs spaced about 12 ft. apart 
framing into a hollow box girder 8 ft. 
high and 6 ft. wide which is supported 
by four columns. The roof has a total 
depth front to back of 108 ft., of which 
40 ft. is cantilevered beyond the col- 
umns. The press box is suspended from 
the roof and connected to the back of 
the stand by a catwalk. George Wel- 
lington Stoddard and Associates, ar- 
chitects; George Runciman and Peter 
Hostmark, structural engineers. 


Western State Teachers College at Kalamazoo, Mich., owns this attractive concrete grandstand. The horizontal rustica- 
tion strips add interest to the surfaces and provide locations for hidden construction joints. Note location of ticket windows 
at entrances. A smaller stand is on embankment on opposite side of field. Osborn Engineering Co., architect and engineer. 


Where the waterstop is horizontal or sloped, it must 
be protected on the top by a joint filler*. It is desirable 
to locate horizontal joints where the traffic is light, that 
is, locating them in aisles is not as good as placing them 
at the edge of the aisles or under the seats. In the latter 
case the continuity of the seats also must be broken. 

In designing and locating expansion joints considera- 
tion must be given to the possibility of the heels on 
women’s shoes becoming caught in open or partly filled 
joints. Consequently the width of joint should be as 
small as construction practice will permit. Where con- 


Metal catch box 
JOINT WITH GUTTER To drainage 


system 


Hie Picea, r-Preformed filler 


TE _ 
SA Al ah lw a 4 


Strap —~—Rust resistant 
gutter 


WITH GUTTER 


1G 0z.copper dam 


WITH DAM OPEN 
SECTION A-A 


Expansion joints in deck. The seat deck is finished with a 
small edge beam on each side of the expansion joint. The joint 
may be made watertight by use of a gutter or a copper dam with 
joint filler. A catch box is essential with the gutter type. A water 
drip should be provided along the edges of the beams for the 
open joint or the joint with gutter. 


26 


Tooled joint filled 


Pitch "in 2:0" away from joint 
with masticr ei a ae 


Tooled joint filled - 
with mastic 7, 


Trowel finish and 
cover with mastic 


ie 


Tooled joint filled 
with mastic Preformed 


filler 


a" x 18" dowels- 
24"0.c.- greased 
end in sleeve 


Trowel finish and 
cover with mastic 


CONTRACTION JOINTS EXPANSION JOINTS 


Expansion and contraction joints in slab or deck on ground. 
Both expansion and contraction joints must be detailed to be 
watertight and to keep the two sides in line. The expansion joints 
must also provide for easy movement. 


siderable traffic will occur over a joint, it may be desir- 
able to install a sliding metal plate over the joint. 
Joints in enclosing walls should be made as in ordinary 
walls of similar materials. Architectural concrete walls 
should have control joints at 15 to 25-ft. intervals in 
addition to expansion joints through entire structure**. 
*List of manufacturers will be furnished in United States and 
Canada upon request to the Portland Cement Association. 
** dditional information is contained in Expansion Joints in Con- 
crete Buildings and Control Joints published by Portland Cement 


Association and available free in United States and Canada 
upon request. 


Construction Joints 


Since the amount of concrete between expansion joints 
is frequently more than can be placed in one day, con- 
struction joints will often be necessary. The location 
_ and construction of these joints, particularly in the deck, 
are of considerable importance. 

There are two procedures commonly used in schedul- 
ing the placing of concrete. Each system has its advan- 
tages and advocates. In both systems the footings and 
columns are placed up to the underside of the sloping 
girders but from there on the order of placing is differ- 
ent. In the first system the entire height of the deck 
and its supporting girders are placed in one day with 
the construction joints parallel to the bents. These con- 
struction joints are usually placed over the center of 
the girders, although they are sometimes made near the 
center of span between bents. In either case, a groove 
should be made at the joint in the tread and this 
groove later filled with plastic material. 

In the second system all the girders between two 
expansion joints are placed before any of the deck is 
cast. The deck is then placed in sections the full length 
between expansion joints, making any necessary con- 
struction joint in a riser. One of the advantages of this 
system is that the construction joint can be made in 
any riser and thus the amount of concrete placed at 
one time can be varied to suit any emergency, whereas 
in the first system it is important that all the concrete 
in a predetermined section be placed continuously. The 
construction joint in a riser should preferably be made 
at the underside of the tread. The joint should be made 
straight (by use of a 1-in. strip temporarily tacked to 
the face form), the surface swept with a stiff broom or 
otherwise treated to roughen it and remove any laitance 
and then soaked just prior to placing the next concrete*. 


Watertight Decks 


Decks should be watertight, at least between expan- 
sion joints, even though it is not planned to use the 
space under the stand. This may be assured by atten- 
tion to a few details of design and construction. The 
entire deck should have a definite slope toward the front 
so that it will drain rapidly. To obtain this effect, each 
tread should be sloped about 1 in. toward the front. 
The water from the deck should be collected at the 
bottom and discharged into a suitable drainage system. 
Simply discharging the water onto the field is not satis- 
factory except in small structures with only a few rows 
of seats. In large structures it is advisable to collect 
the water at intermediate points in the deck height so 
that it may be removed more quickly and excessive 
amounts of water will not flow over the lower treads. 
As an average, | sq.in. of drain pipe should be provided 
for each 300 sq.ft. of deck. 

To reduce the amount of water flowing over expansion 
and construction joints, the treads are sometimes pitched 
away from the joints. This may be done by a %-in. 
increase in the thickness of the tread made gradually 
over a distance of 2 or 3 ft. on each side of the joint. 

With good quality concrete and reasonable care in 
design details and construction, the deck can be made 
watertight so that the space beneath may be used 
without other protection. However, in a number of 
instances only a portion of the space has been used so 
that a standard type of roof has been installed over the 
rooms to reduce the ceiling height or as protection from 
the unenclosed area above. 


*A dditional information is contained in Bonding Concrete or Plaster 
to Concrete and Construction Joints published by Portland Cement 
Association and available free on request in United States and 
Canada. 


The grandstand at Nyack, N. Y., was built on an embankment, with a passage at one end to a dressing room. To permit 
winter construction, a heated enclosure covering one section was used and moved on rollers as construction progressed. 
Henry G. Emery and George N. Schofield, associated architects; Harvey Polhemus, engineer. 


27 


Structures on Embankment 


Where the topography is such that the seats can be 
built on an embankment, the construction costs may 
be reduced. However, some of the saving in cost of the 
seating structure is offset by loss of the usable space 
under the seats. Except for very small structures or for 
those adjacent to existing gymnasiums or similar build- 
ings, space must be provided under the seats or in 
adjacent buildings for the facilities previously discussed. 

There is considerable variation in the general types 
of grandstands built upon embankments. One type is 
practically the regular framed structure, simply having 
short columns supported on the embankment. The only 


Seats on each hide AAS OL oh: 


Trowel finish and 
cover with mastic 


Trowel finish and 
cover with mastic 
2:0" to 4-O"depending 
on frost depth 


Pear are Ria 


“Floor drain 
3"C.1. pipe - connect to 
concrete pipe drain ! 

ALTERNATE DETAIL SHOWING 

WALK AT FRONT OF GRANDSTAND 


saving with this type is in the shorter columns and less 
bracing. At the other extreme is the solid slab cast on 
the plane surfaced embankment. Between these two 
types are many variations, the choice depending on 
local conditions such as type of soil, climate, pitch of 
seats, available equipment, and relative cost of ma- 
terials and labor. An intermediate type which has been 
used when the soil is quite firm consists of the concrete 
deck cast on the soil, which has been cut in the form of 
steps parallel to the top surface of the stand. 

The greatest economy will be obtained by designing 
these structures simply as slabs supported directly on 
the ground. However, where built upon a poorly con- 


2hi0" 5+0* 


Pitch a" per bee 


| 

cover with mastic 
Grave} 

trench | | 

Concrete pipe drain. | 

May be omitted ifat. | | 

| 


top of em bankment —+€ ) | 


afl 
is xpansion joint 
ee : 
§5 
A 
wd el = 
v ‘2 
- ye 20" 
a ees 
Qe) fokZor -’\—3"C.1. pipe thru wall - : 
oY! bo 2 pera 
BU qe ES} connected to concrete : ane) od 
e 8 aac pipe drain outside wall “> Trowel Ainichrana 
Pe cae cover with mastic 
= oO| [[Uheovo 
ok 
a 8" 
aa e os : Concrete pipe drain. 
; ee _ |May be omitted if at 
ae a o|top of embankment 
Ss ge cover with mastic Jy. 
rs ra Expansion Practeo 
€£ joint k 
A oe ote] Grade line 
5 =% Qe |_ Gravel 
= ne i s} )2*), trench 
iz inet Note Opt | Sell 
on id At ends of stand use 6"wall 2-0: Sis 5 sll 
o . eh extending below frost line. NS et eee 
SE Apes / Transverse expansion joints M5 * | ; Sa 
2s {s _~3"C.L pipe thru wall at 60' intervals with contraction S14] 2 Si 
= Ol bar Ouse joints at 20'intervals. hon Oil eal 
roo had Br A to connected to concrete JOINTS a Pa an pede 
= 6} lercd: pipe drain outside wall egea eer oI 
ee “4 peer ballincy iI 
cee ees pe) axl 
wu 5° Pepe GC} drain 
vo = ——— 
: se 8 
ao ' “ 
5-0 
Pk - ALTERNATE DETAIL TOP OF 
cS) High point : 
- herwecraIGeraeninee GRANDSTAND SHOWING WALL 


Typical designs for grandstand on embankment. The two general schemes are shown in which the deck is cast on an embankment 
cut as steps or cut as a plane. The alternate details of front and back are applicable to either general scheme. 


28 


The natural site permitted this grandstand at Anniston, Ala., to be built on an embankment. Entrance is from the top. 
Note the curved back which gives larger percentage of seats opposite the centerline. A small, well located press box is 
provided. Side walls are appropriately low for the hillside location. R. L. Kenan and Associates, engineers. 


solidated embankment, the structure may have to be 
built on walls or columns extending to good founda- 
tions, thus neglecting the supporting power of the soil 
under the seats and using it only to save the cost of 
formwork. 

Regardless of the type of structure used, it is im- 
portant to reduce to a minimum the water entering the 
embankment. Surface water should be intercepted and 
drained away before reaching the structure. Unless the 
top of the stand is at the top of the embankment, a 
cutoff wall and drain tile should be provided at the 
top of the structure. Drains should be placed at the 
bottom of the slope also. 


The grandstand at Fraser Field, Lynn, Mass., is placed so 
that entrance at top of stand is made by short ramps from 
street level. A wide circulating aisle is provided in back of 
seats. The cantilevered concrete roof covers a large part 
of the stand. Note elevated press box under roof. C. R. B. 
Harding, engineer. 


Roofs 


In general, roofs are not provided on grandstands 
used primarily for football and track but are provided 
over at least a portion of stands used for horse races 
and professional baseball. 

In designing roofs every effort should be made to 
eliminate or reduce to a minimum the interference to 
spectators’ view caused by supporting members. Canti- 
levering all or part of the roof removes or reduces this 
interference. The sweeping lines of reinforced concrete 
cantilever roofs add to rather than detract from the 
appearance of the entire structure. Also, such roofs are 
firesafe and do not require periodic painting. 


CONSTRUCTION 


Quality Concrete 


In grandstands a very large surface area is exposed 
to the destructive forces of weathering. Therefore, not 
only is correct design essential, but good quality con- 
crete work is necessary to produce a structure that will 
successfully resist the elements and continue indefi- 
nitely to present a pleasing appearance. Specifications 
for the work should be carefully prepared and super- 
vision of the construction should be competent to see 
that the specifications are observed. 

The technique of concrete making has been developed 
to such a degree that structures can now be built with 
assurance they will give long life service with a mini- 
mum of maintenance. The quality of concrete is de- 
pendent on the characteristics and proportions of the 
materials, and on the care used in placing and curing. 

All materials should comply with the standards of 
the American Society for Testing Materials. 

The resistance of concrete to weathering and its 
watertightness, strength and other qualities are largely 
established by the proportion of water to cement*. For 
grandstands in the northern latitudes of the United 
States it is recommended that the water content does 
not exceed 6 gal. of water per sack of portland cement. 
In the southern states it may be increased to 7 gal. per 
sack. These amounts include any free surface moisture 


introduced with the aggregates, for which a correction 
must be made. 

The proportions will depend on the grading of the 
materials, method of placing and the shape of the 
section to be placed. It is important that the concrete 
mixture be of a plastic consistency that can be placed 
easily, but will not allow segregation of the materials 
and excess water to accumulate in the corners and on 
the top surfaces. Such segregation often results in 
stone pockets, and edges and top surfaces that have 
poor resistance to weather. 

Methods of placing concrete should be chosen that 
will maintain uniformity in the mixture and produce 
a completed structure of uniformly high quality. In 
some cases concrete has been distributed by chutes 
from a central tower. When necessary to carry concrete 
over long distances there is a tendency to use chutes 
on too flat an angle (less than 1 vertical in 3 horizontal) 
to avoid an excessively high tower. This practice should 
be discouraged as it requires a very wet or “‘sloppy”’ 
concrete and results in almost certain segregation of 
the materials and poor weather-resistance in the fin- 
ished structure. 


* 


*Additional information is contained in Design and Control of 
Concrete Mixtures published by Portland Cement Association 
and available free in United States and Canada upon request. 


A feature of the grandstand at Strobel Field, Sandusky, 
Ohio, is the concrete cantilever roof. Note the long dug- 
outs, enclosed press box and location of aisles at one side 
of vomitories. Harold Parker, architect; R. C. Reese, engi- 
neer. 


Placing concrete in the seat deck. Concrete is placed from 
a bucket handled by a crane. This permits direct placing at the 
desired location in the forms without chutes, an important step 
in the prevention of segregation of the ingredients and in pro- 
ducing uniform concrete. The forming shown in sketch below 
is being used with loose planks on supports tacked to riser forms. 


Most engineers prefer that the concrete be carried 
in buggies or in bottom dump buckets handled by 
cranes to spot the bucket in the exact position for de- 
posit of the concrete. When buggies are used, they are 
pushed over runways and short lengths of chutes are 
used from the runway to the forms. Chutes should dis- 
charge the concrete into hoppers and not directly into 
the forms. Both buggies and buckets have the advan- 
tage of keeping the concrete in small batches in which 
there is less tendency for segregation before it arrives 
at the point of deposit in the forms. The smaller batches 
can be placed in the forms in the desired locations so 
that little movement is necessary after the concrete is 


Deck forming. This sketch shows one of the best of the many 
methods of forming the underside of the seat deck and the risers. 
The deck forming is simple to erect and strip so that several 
reuses can be obtained. It can be used with various other types 
of front riser forms including that shown to the right. The large 
stringers permit a wide spacing of T-shores. The special form tie 
also serves as a means of attaching the seat supports, the bolts 
in the front being replaced by permanent bolts through the seat 
support. Beveling the front riser form as shown provides a small 
fillet and makes finishing easier than beveling the opposite way. 


Men on upper plank are spading and rodding concrete into place. 
The fourth tread is being screeded to proper pitch while second 
tread is being troweled lightly. Treads were later given a light 
brooming. The supports and planks provide a good working plat- 
form with a minimum of interference in the finishing operations, 
thereby speeding up the work and improving the finish. 


deposited. Whatever methods of transporting and 
placing are used every precaution should be taken to 
maintain the concrete in a uniformly plastic mixture. 

When concrete has been placed in the forms it should 
be thoroughly puddled or vibrated to compact it, to 
thoroughly embed all reinforcing steel and fixtures and 
to provide smooth surfaces along the forms. The order 
of placing concrete will depend on the design and 
personal preference as discussed on page 27. Particular 
attention should be given to placing concrete in the 
deck slab as it will be exposed to the most severe 
conditions. Placing in the deck is started on the lower 
tread and riser, from one end to the other of the 
section. Concrete is then placed in the second tread 
and riser beginning at the same end of the section as 
before. This procedure is carried on continuously from 
bottom to top of the section. The rate of placing 


This form assembly is made in movable units with 12-ft. plank 
stringers and riser forms. The units are fastened together with 
the scabs marked fF, The units must be carefully anchored in 
place. Note the 2x4 struts at the lower end of each stringer and 
the tie wires to the seat support bolts. The tops of the stringers 
are supported on and tied to the forming for the underside of 
the deck. A plywood facing with open backing is frequently used 
in place of the kerfed plank riser form shown. 


31 


Texture was produced 
on the concrete walls of 
the grandstand at Iola, 
Kan., by accentuated 
joints between form 
boards. Incised letter- 
ing was cast above the 
main entrance. Garrold 
Griffin, architect. 


should be fast enough 
to avoid the formation 
of joints between suc- 
cessive steps but 
should be slow enough 
so that the concrete 
can be thoroughly 
puddled into the forms 
and around the rein- 
forcing steel. 

Reinforcement should be carefully placed and firmly 
held in position during placing of the concrete. It is 
especially important to keep the reinforcement away 
from exposed surfaces. A point where very careful 
placing is necessary is at expansion joints. Where 
copper dams and premolded filler are used in the joint, 
care is required to maintain proper position of the dam 
and filler and to embed the wings of the dam thoroughly 
in dense concrete. The concrete should be carefully 
tamped into place in these locations. No concrete or 
mortar should be allowed to flow into the joint as this 
would interfere with its operation. 

Proper curing is one of the most economical means of 
improving the quality of concrete. By proper curing 
is meant the provision of conditions favorable to harden- 
ing of the concrete, namely: (1) temperatures above 
50 deg. F. and (2) prevention of too rapid drying of the 
concrete. Leaving the forms in place is very helpful in 
retaining moisture in the concrete. All exposed surfaces 
should be kept continuously moist for at least 5 days, 
except that for high early strength portland cement 
concrete moist curing may be reduced to 2 days. In 
cold weather construction, necessary precautions 
should be taken to protect the new concrete from low 
temperatures*. 


Finish 

Tie wires passing through the concrete should not 
be permitted in grandstand construction. Form ties 
should be of a type that is entirely removed from the 
concrete or leaves no metal closer than 11% in. to the 
exposed surface. Holes left by ties should be filled solid 
with mortar before other finishing or cleaning opera- 
tions. 

With good form construction and careful placement 


32 


Printed in U.S. A. 


of the concrete, attractive surfaces can be obtained 
which require no other treatment than knocking off 
an occasional small fin and suitable cleaning. Plywood 
and wood-fiber board are widely used as sheathing or 
lining for forms to produce pleasingly smooth surfaces. 
Since these materials are available in large sheets, 
there is a minimum of joint markings from the forms 
and these can be fitted into the architectural design or 
can be practically eliminated if desired. A wide variety 
of rougher textures can be produced by using lumber 
of different kinds, sizes and finishes*. 

Walkway surfaces which include ramps and stairs 
should be given a nonslip finish. One method of doing 
this is by floating and troweling the surface, then 
brooming it. A fiber or bristle broom can be used 
depending on the texture of surface desired. If the 
treads of the seat deck are to be broomed, this should 
be done across the width of tread as broom marks 
parallel to the length may interfere with quick drainage 
from the treads. Care must be taken to maintain the 
specified slope from back to front of these treads for 
good drainage. 


ACKNOWLEDGMENTS 


The same details have been used so frequently on 
more than one grandstand or by more than one designer 
that it is impossible to know who is responsible for 
their original use. The details shown have been taken, 
with some modifications, from drawings kindly fur- 
nished by many architects and engineers, to whom the 
Portland Cement Association expresses appreciation. 


*A dditional information is contained in Concreting in Cold Weather 
and Forms for Architectural Concrete published by Portland Cement 
Association and free in United States and Canada upon request. 


S-30-2 


R ridge Decks 


* 
* 


ee ST concrete construction provides a speedy 
and economical method for erecting new bridges 
and for replacing worn bridge decks. The purpose 
of this booklet is to acquaint engineers and build- 
ers with various types of precast concrete bridge 
decks that have been built; to point out techniques 
involved in precasting and erection procedures, 
and to describe some of the conditions under which 
precast concrete construction is advantageous. 

Economy achieved with precast units in bridges 
results chiefly from re-use of formwork that dupli- 
cation of parts makes possible. This advantage is 
greatest when precasting is done in established 
casting yards or manufacturing plants located near 
sources of materials and labor. Further economies 
arise because precast construction eliminates most 
falsework and shoring at the bridge site, and re- 
quires only a small construction crew. 

The adaptability of precast construction adds 
to its usefulness under diverse conditions. It is 
particularly advantageous in isolated places where 


labor and materials are not readily available. It 


facilitates the bridging of swamps where erection 


INTRODUCTION 


of centering is difficult and the crossing of railroads 
and highways where construction interferes with 
traffic. It is also well suited for structures crossing 
large bodies of water since it eliminates many of 
the inherent dangers of construction over open 
water. 

Use of precast units permits rapid repair or 
replacement of existing structures with minimum 
interference to traffic and avoids the inconvenience 
of long detours. Where precasting is done in a 
central plant uniform control may be maintained 
and better quality concrete is more readily at- 
tained. Precast concrete construction has the same 
qualities of durability and fire- and termite-resist- 
ance that are associated with cast-in-place con- 
struction. 

These and other advantages indicate the broad 
field which exists for precast concrete bridges. The 
types illustrated in this booklet are intended to 
point out a few of the successfully used designs 
and to stimulate interest in development of new 
designs and improved techniques in manufacture 


and erection procedures. 


Fig. 1—The casting platform for the 
Baker River Bridge in Washington con- 
sisted of a solid wood deck. 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technica 
service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold progran 
of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged ir 
the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request 


COPYRIGHT 1953 BY PORTLAND CEMENT ASSOCIATION 


Precast Concrete Rridge Decks 


GENERAL CONSIDERATIONS 


Casting Yard 


Proper location and layout of the casting yard are 
important considerations for both temporary and per- 
manent installations. Among the conditions governing 
location are availability of materials and labor and the 
adequacy of transportation to bring in materials and 
equipment as well as to move the finished product to 
the erection site. Usually highway or rail transportation 
is necessary but for large marine structures ready access 
to water transport may be advantageous. 

The yard should be level, well drained and large 
enough to provide ample space for the various precast- 
ing operations and for the storage of cement, aggre- 
gates, reinforcement, forms and the finished precast 
products. Some form of shelter will facilitate operation 
during inclement weather. The yard should be equipped 
with a casting floor which will not settle under antici- 
pated loads. This may consist of a concrete platform and 
should be placed only after all soft ground has been 
drained and compacted. 

The layout of the yard and particularly of the casting 
area should be suitable for maintaining the necessary 
production schedule. A typical layout is illustrated in 
Fig. 1. Equipment used in the yard for handling the 
precast units will depend upon their size and weight. 
Provision should be made for the ready movement and 
operation of this equipment in unloading and placing 
the reinforcing steel, placing the concrete and in hand- 
ling the finished product. A production-line layout that 
will permit simultaneous operation of all phases of the 
precasting process will result in economy. 


Formwork 


The formwork to be used will depend on the size and 
design features of the units to be cast and on the number 
of times the forms are to be re-used. Concrete, metal, 
wood or combinations of these may be used. If the in- 
tention is to duplicate the precast elements for more 
than one bridge and in general to provide for inter- 
changeability of parts, concrete or metal forms are 
advantageous since, with proper care, they may be 
re-used an indefinite number of times. Wood forms are 
satisfactory if a limited duplication is anticipated. In 
many cases a concrete casting platform is satisfactory 
as the bottom form for beams and slabs while the side 
forms may be of wood or metal. In at least one case, 
where each precast element consisted of a combination 
of slab and beams, the entire form was of concrete with 
a metal liner provided for all but horizontal surfaces. 
This mold is shown in Fig. 2. 

Fig. 3 shows beam forms made entirely of wood and 
supported by 4x12-in. timbers embedded in the ground. 
Such a form lends itself to precasting beams of various 
lengths and depths by using movable end and bottom 
pieces. 

Fig. 4 shows a form used by the South Carolina State 
Highway Department. Here, one complete span of the 
bridge deck is cast at once, but is separated for handling 
purposes into slab and curb units by longitudinal divid- 
ing strips of steel. The units are erected at the bridge 
site in the same relative positions they occupy in the 
casting yard, thereby assuring a correct fit. 

It is essential that all formwork be designed for ready 


Fig. 2—Concrete forms used in precasting combination Fig. 3—Formwork for precast concrete beams placed on a casting platform sup- 
beam and slab deck units. To facilitate removal of units, ported on timbers. Bulkheads may be adjusted for beams of different lengths. 


metal sheathing is provided for surfaces not horizontal. Blocks at ends of forms are used to mold shear keys at top surfaces of beams. 


Fig. 4—Precasting one complete bridge span for the South Caro- 
lina State Highway Department. Metal strips separate slabs. 


assembly and disassembly without damage to either the 
form or the precast concrete member. Form sections 
should fit tightly to prevent leakage and should be 
braced firmly so that correct shape and position will be 
maintained during the placement and vibration of the 
concrete. Forms should be well oiled before use, or, if 
of wood, they may be moistened with water. Oiling 
should be done prior to the placing of reinforcement to 
preclude the possibility of oil coming in contact with it. 
Oil adhering to the reinforcement would impair the 
bond between concrete and steel. 

Definite tolerances in the formwork should be speci- 
fied for variations in straightness, length, width and 
depth. Close tolerances must be maintained when the 
joints between adjacent precast units are to transmit 
shear through contacting surfaces. This type of joint is 
illustrated in Fig. 13a (page 7). However, precasting 
schemes involving wide joints to be filled with cast-in- 
place concrete, as shown in Fig. 20a (page 12), do not 
require such precision since slight irregularities in sur- 


Fig. 5—Erection of precast concrete bridge deck slabs in Lowell, 
Mass. See Fig. 15 for details. 


Fig. 6—Proper vibration allows the use of less mixing water and 
results in concrete of higher strength and greater durability. 


face elevations may be smoothed out in the joints. In 
general, the precision required will depend upon the 
design and function of the particular elements involved. 

In constructing the Plain Street Bridge at Lowell, 
Mass., which utilized deck slabs similar to those illus- 
trated in Fig. 5, it was found that l-in. tolerances 
were easily obtained for units 5 ft. wide and 171% ft. 
long. The same tolerance was found satisfactory for the 
Baker River Bridge in Washington (see Fig. 22a page 
14), where precast stringers were 10 in. by 24 in. by 
25 ft. long and precast deck slabs were 8 ft. 4 in. by 
4 ft. 2 in. by 6 in. thick. The precast beams shown in 
Fig. 26 (page 17), are provided with a small shelf at 
either side near the bottom to support forms for the 
cast-in-place deck. If the width and lateral spacing of 
the beams are held to close tolerances, economy of 
construction is realized through repeated use of pre- 
fabricated formwork for the deck slabs. 


Concrete and Reinforcement 


It is essential that the steel reinforcement be firmly 
tied and held in position in the forms to avoid displace- 
ment during placing of concrete. It is often advan- 
tageous to preassemble the steel into cages for beams 
and girders. 

The basic principles for making portland cement 
concrete should be followed carefully to produce those 
qualities required in the finished product. * Air-entrained 
concrete is recommended for deck units which will be 
exposed to severe frost action and to salts used for 
removal of snow and ice. 

Compacting the concrete by vibration, as illustrated 
in Fig. 6, allows the use of stiffer mixtures which result 
in increased compressive and flexural strengths and in- 


*See Design and Control of Concrete Mixtures available free in 
U.S. and Canada from the Portland Cement Association. 


Fig. 7—Precast girders for a bridge in Lowell, Mass., are trans- 
ported on a low-bed trailer and are handled by a mobile crane. 


creased resistance to weathering. Vibrators should be 
used, however, to compact the concrete and not to push 
it laterally in the forms. 

Curing by steam accelerates production, reduces the 
amount of formwork required and permits maintenance 
of smaller stockpiles of the completed units. Steam 
curing is also advantageous in cold weather. 

Since precasting in a yard permits close control over 
the proportioning of the concrete mix and over all other 
operations, an increase in the specified cylinder strength 
of the concrete has been allowed in some instances. 

If lightweight concrete is required for precast units it 
may be produced with special aggregates such as ex- 
panded shale, burned clay or expanded slag. Mixtures 
for lightweight concrete should be designed to produce 
the required strength and weight, and tests should be 
made to verify the results. 


Handling and Storage 


Proper handling of precast units is important to both 
designer and builder. Faulty design for bending stresses 
or improper handling of units in the field can result in 
serious cracking of the concrete. 

The method of pickup should be determined by the 
designer and the units then designed to carry the 
stresses involved. The number and location of pickup 
points will depend upon the weight and shape of the 
piece and on the type of handling equipment used. In 
general, two or more pickup points may be located 
symmetrically about the center of gravity of the unit 
to minimize handling stresses, and equalizing devices 
may be specified to produce known lifting forces at 
these points. The pickup points should be marked on 
each unit together with an indication of the correct 
handling position for which the unit was designed. It 
is reasonable to allow somewhat higher stresses for 
erection loads than for normal service loads. However, 


Fig. 8—Placing precast concrete slabs for a bridge in Miami, Fla. 
Note wood blocks and hangers for support of joint formwork. 


units should not be handled before sufficient strength is 
attained. Care should be taken to insure that pickup 
devices will be adequately anchored to withstand 
stresses induced by handling. 

Steel reinforcement protruding from the faces of the 
precast units may be used for handling provided these 
bars possess sufficient strength. Fig. 7 indicates a 
method of pickup using two steel bars temporarily 
passed through 2-in. pipe sleeves in the beam. Fig. 8 
shows a sling passing completely around a precast slab. 
The latter two handling devices may not be satisfactory 
when elements are to be placed directly against adjacent 
units, since the bars or sling will prevent close contact. 
A more useful pickup in this situation is illustrated in 
Fig. 9 where looped steel rods project above the con- 
crete surface. With this scheme, depressions may be 
formed in the concrete where the steel rods enter the 
slab. When the slab is in its final position in the bridge 
these rods may be cut or burned off close to the concrete 
and the depressions filled with mortar. 


Fig. 9—Partly completed precast concrete bridge deck in Monroe 
County, Pa. 


Fig. 10—An automobile wrecker truck was part of the equipment 
used for the Baker River Bridge in Washington. 


The designer may also consider pickup devices which 
will facilitate stockpiling. When precast units are to be 
stored for future use, pickup devices protruding from 
horizontal surfaces may be inconvenient, and threaded 
inserts or anchors which will receive threaded eyebolts 
may be better. The combined bolt and insert unit may 
be set into position in the fresh concrete and the bolts 
turned later to break any bond that may be created be- 
tween the bolt surface and the concrete. This will leave 
the nut or insert fixed in the concrete while the bolt is 
removable. Holes left when the bolts are taken out after 
erection may be filled with a mastic which can be re- 
moved should future road conditions require that the 
bridge be changed or moved. 

The designer should give consideration to the type of 
handling equipment contractors may use. Frequently 
this equipment will be the governing factor in determin- 
ing maximum weights and sizes. For the construction 
of precast bridges in Lowell, Mass., available equip- 
ment made possible the use of beams 52 ft. long and 


Fig. 11—Loading precast girders for transport in Spokane County, 
W ash, 


weighing 12 tons each (see Fig. 7). 

In general, contractors prefer to use highly mobile 
hoisting equipment. Fig. 10 illustrates an ordinary auto- 
mobile tow truck placing a deck slab, and Fig. 11 shows 
a truck crane loading precast girders onto a trailer. 
Other methods of handling include the use of a derrick 
mounted on a barge or boat, a pile driver equipped with 
a swinging boom, or a temporary monorail. One method 
of unloading precast units at the bridge site is illus- 
trated in Fig. 12. Here, the precast unit is moved on 
rollers down a timber ramp from the trailer. 

Precast units may be stored by stacking them with 
or without separating blocks. Fig. 11 illustrates the 
former method in a casting yard near Spokane, Wash. 
The procedure to be followed will depend on many fac- 
tors including the type and location of handling devices, 
curing conditions and available space. When blocking 
is used between tiers it should be kept in vertical lines so 
that the weight of the upper units does not produce 
bending in those of a lower tier. 


Fig. 12—Unloading deck slabs at a bridge site in Scott County, Ky. 


PRECAST CONCRETE BRIDGE TYPES 


ie. details illustrated in Figs. 13 through 29 represent 
several types of precast concrete construction which 
have been used for highway bridges and also indicate 
various techniques that may be applied to precasting. 


Figure 13 

This design requires no cast-in-place concrete—an 
important consideration in some situations. 

As indicated in Fig. 13b, four 5-ft. wide interior slab 
units and two 2-ft. wide exterior curb and handrail units 
are involved. Spans up to 14 ft. have been built with an 
814-in. slab thickness, and for this case, interior and 
exterior units each weigh 7200 and 6300 lb. respectively. 
All six units making up one span for this particular 
bridge are cast together on a platform as shown in Fig. 
4 and are separated from each other by dividing strips 
of 10-gage sheet metal bent in a <- shape. Relative posi- 
tions of the six units are the same in the final structure 
as in casting, so that the joints fit closely and provide 
satisfactory lateral transfer of shear. 

Each interior unit has two holes at one end and one 
at the other. These holes are used with a pickup device 
in handling the unit and later to secure the slab in its 
final position. Bolts are passed through the holes to 
fasten clip angles to the bottom surface of the slab as 
shown in Fig. 13c, thereby assuring that the deck and 
pile cap remain in the same relative position at all 
times. Boltheads are countersunk. The ends of the slabs 
have horizontal, semicircular grooves cast along their 
centerlines to form a transverse hole when two slabs 
are butted over a pier. When all units are in position at 
a pier, a l-in. round copper-bearing steel rod with 
threaded ends is passed through this hole. The rod ex- 
tends outside the curb units and plate washers and nuts 
on either end are tightened to tie the entire roadway 
together. Exposed portions of the tierod assembly may 
be painted to prevent corrosion. 

Rectangular-section precast concrete pile caps are 
cast with l-in. dia. holes centered over the piles. Dowels 
are driven through these holes into the piles below and 
the holes are then filled with grout. 

Although this method of precasting does not permit 
interchangeability of parts, the excellent fit of the joints 
produces a roadway which requires no additional wear- 
ing surface. The weight and size of the individual units 
facilitate transportation and erection, as evidenced by 
the installation of a 7-span bridge in four days by a 6- 
man crew of the South Carolina Highway Department. 


handrail and curb of ice accumulation 
all interior spans 


= Open joint between [oes to prevent 


Precast units - 


l-in.rd tierod 


Hole for handling and for 


attachment of clip angle ocr aoe 


a. CUTAWAY VIEW OF CURB AND INTERIOR 
SECTIONS AT SUPPORT 


6' 6" 22'-O" curb to curb 


Symmetrical about te A 


l-in. rd. tierod ~] 


Paint bolts 
and washers 


Pier or pile cap 


b. TRANSVERSE SECTION 


Handrail and curb unit 


Hole for |-in.rd.tierod 


Dowels fastening pile 
cap to piles 


14'-0" 
c. SECTION A-A AT SUPPORT 
Fig. 13—Precast concrete bridge construction developed by the 


South Carolina State Highway Department. Grooves between 
units are designed to provide lateral transfer of loads. 


“I 


Precast post 


10'-O' curb to curb 


Precast beam 


J ( Kh pf y ve cz y AY. j C4 Wi f 


44 
ri Py 


LAN fas A 


4 Lf Ph 


Fig. 14—T-shaped precast units which form the bridge deck allow 
rapid construction and require no cast-in-place concrete. 


Figure 14 

A precast bridge developed in England for the tem- 
porary replacement of damaged bridges is illustrated 
in Fig. 14. Since the purpose is to eliminate as much 
cast-in-place concrete as possible to allow rapid erec- 
tion in an emergency, the bridge is entirely precast 
with the exception of the curbing. The cast-in-place 
curbs may be constructed without interference with 
traffic. The details presented are for a single-lane bridge 
of 20-ft. span and clear roadway width of 10 ft. The deck 
consists of T-girders placed side by side with <-shaped 
joints between adjacent flanges. To insure proper fit at 
these joints, the seven units for one span are cast to- 
gether in the same relative positions they will have in 
the completed structure. Each unit has a 5-in. flange 
which forms the deck. The web in which the longitudinal 
tensile reinforcement is placed is 914 in. deep and 7144 
in. wide. The girders are held together transversely by 
two 114-in. round tierods which pass through openings 
in the webs just below the flanges. The ends of the rods 
are bolted to the flange of a 7x31%-in. steel channel set 
against the exterior T-girders. These channels are also 
drilled to take 1-in. bolts which in conjunction with 
5g-in. bolts cast in the curbs serve to hold four precast 
concrete fence posts in position at each side of the bridge. 
At the ends of the span, precast concrete block are fitted 
into the openings between the flanges and the bridge 
seat and are grouted to create a solid abutment to retain 
the roadway fill and to give additional rigidity to the 
beam supports. This closure may also be cast-in-place 
concrete. 

Joints between adjacent units are held tight by trans- 
verse tierods and effect lateral distribution of the wheel 
loads. By taking advantage of this unity of action the 
designer will achieve economy of materials as well as 
less dead weight. The units illustrated weigh 3800 lb. 
each for a 22-ft. length. 

This design may be modified for use over several 
spans, and continuity over intermediate supports may 


8 


be obtained by lapping or welding top reinforcement 
and then closing the gaps between adjacent members 
with concrete. 

Another modification involves the precasting of units 
having thin flanges which are supplemented on the site 
by a layer of cast-in-place concrete. Such an arrange- 
ment loses some advantages of an entirely precast 
structure, but does produce a highly integral deck which 
assures lateral distribution of the loads. Under these 
circumstances, the tierods are unnecessary. 


Figures 15-17 

Precast units of channel-shaped section have been 
used extensively for short-span bridges to obtain greater 
strength with a minimum of dead weight. Design is 
based on the assumption that a pair of adjacent ribs 
will act as one unit. Shear keys filled with portland 
cement mortar after the slabs have been set in final 
position provide unified action and thereby distribute 
the loads laterally. Thus, the load carried by each pre- 
cast element is less than a full wheel load, making possi- 


Holes for anchor rods 
Lifting loop 


Slot to receive 
U-shaped dowel 


Shear key to be 
filled with mortar 


EATS 


MOREL, 7 
M 
J 


ortar bed or premolded 
joint filler 


a. CuTaAway View NEAR SUPPORT 


Shear key 


———— SS a 


lOy 


Pier or pile cap 


b. TRANSVERSE SECTION 


Holes for anchor rods 


Ona Wa. ras a 


—} tress 


Pier or 
pile cap 


C. LONGITUDINAL SECTION 


Fig. 15—A precast bridge in which units are tied together by 
dowels. Units are designed on the assumption that a pair of ribs 
will carry one wheel load. 


ble an economical design with no sacrifice of rigidity. 

Each of the three channel slabs shown illustrates a 
shear key of slightly different design. These or other 
types of keys may be used as long as the requirement of 
shear transfer is fulfilled. Although the slab is not con- 
tinuous laterally over the supporting ribs, it is precast 
integrally with them, so tensile stresses exist at its 
upper surface in the vicinity of the ribs. Therefore, top 
lateral reinforcement should be designed for a continu- 
ous condition and bottom reinforcement should be 
designed on the assumption of simple supports at the 
ribs. 

The longitudinal T-beams are often designed for 
simple spans although continuity over intermediate 
supports can be obtained as discussed on page 18. 
A uniform bearing surface on the bridge seats may be 
obtained for the precast units by setting them on a 
mortar bed. Shear keys and transverse joints between 
adjacent units over intermediate supports may be filled 
with cement mortar to within one or two inches of the 
top surface and the remainder of the joint filled with a 
mastic material. 


Figure 15 


The units in Fig. 15 were designed for a 1714-ft. span 
and for the H20-44 loading of the AASHO* specifica- 
tions. Precast units of the inverted U-type are generally 
used for spans of 20 ft. or less, although longer spans 
have been erected. In this design, each pair of ribs car- 
ries one entire wheel load of 16 kips, and the rib depth 
is such that no stirrups are required for diagonal tension. 
To assist the shear key in distributing loads laterally, 
adjacent units are tied together transversely. Fig. 15a 
illustrates slots provided for this purpose in the top 
surface of adjacent units. U-shaped steel dowels are 
placed in these slots which are then filled with mortar. 
Vertical holes cast near the corners of each unit are 
aligned over similar holes cast or drilled in the supports 
to receive steel anchor dowels. After these dowels are in 
place, the remaining space may be filled with grout. In 
Lowell, Mass., 18 slabs of this type were placed in 414% 
hours by four men plus a mobile hoisting rig and its 
crew. The weight of one 1714-ft. unit is approximately 
11,500 Ib. 


Figure 16 


The details in Fig. 16 have been adapted from a de- 
sign of the West Virginia State Road Commission and 
are for a structure having a roadway width of 22 ft. 4 in. 
and overall width of 24 ft. The deck consists of six in- 
terior units and two curb units, each 3 ft. wide. The deck 
is designed for the H15-S12-44 loading. Allowable 
stresses are 20,000 psi in the reinforcement and 1500 psi 


*American Association of State Highway Officials. 


Holes for 


Shear key filled 
anchor rods 
NN 


with mortar~ 


4" bremolded 
Calked joint joint filler 
Curb unit 


Lifting 


Interior unit 


Stiffener Pipe sleeve to 
receive shear 


bolt 


Pier or pile cap 


a. Cutaway View NEAR SUPPORT 


8" Shear key filled 


ve with mortar 


b. TRANSVERSE SECTION 


Holes to receive 
anchor rods 


cit ty Stiffener . 
ee spaced at / 
| 6-0" 0.6; 


26'- Ou 


C. LONGITUDINAL SECTION 


Fig. 16—Channel-shaped precast units utilize T-beam action of 
adjacent ribs for support of live loads. 


in the extreme concrete fiber, based on a 28-day com- 
pressive concrete strength of 4500 psi. 

The bridge seat is cast with a 114-in. parabolic crown 
and the precast units are placed on bearing pads of 14- 
in. premolded joint filler. The lower 9 in. of the longi- 
tudinal joint surface is given one coat of asphalt paint 
prior to erection. 

Units of this kind have been made using concrete 
forms for the inside surfaces. A unit 16 in. deep and 
26 ft. long weighs approximately 9000 lb. and is handled 
by four lifting loops, a pair being placed approximately 
at each of the outside quarter points. The ends of the 
slabs may be built to conform to any angle of skew. 


Shear key to be 
filled with mortar 


2+" Lifting hole 


e) ws Ge 
6" Sc0m 1166 mee 6" 
4-0" 220% zo _| 


b. TRANSVERSE 


SECTION 


Fig. 17—Lateral distribution of live loads to adjacent precast 
slabs is effected by shear keys placed between units. 


Figure 17 


The width of each channel slab illustrated in Fig. 17 
is 4 ft., six such units giving an overall deck width of 24 
ft. The units are alike except that curbs are cast integ- 
rally with the two outside slabs. 

For a 15-ft. 9-in. overall length of deck designed for 
H15-44 loading, the total depth includes a 41%-in. slab 
plus a 151%-in. rib. For these design conditions there are 
four tensile bars in the bottom of each rib, the bars being 


bundied as shown. All four bars are hooked and the two 
in the upper layer are stopped short of the end of the 
unit. Bundled reinforcing bars have been used satis- 
factorily in many precast and cast-in-place concrete 
bridges in Washington. By bundling bars of small cross- 
section, the resulting decrease in web thickness will 
reduce the weight of the member. 

A 4500-psi concrete strength is specified for these pre- 
cast units and the maximum allowable stresses are 1500 
psi in the concrete and 20,000 psi in the reinforcing steel. 
A typical interior unit weighs approximately 6000 Ib. 


Figure 19 

Fig. 19 illustrates portions of a precast concrete bridge 
design which has been developed by the California 
State Highway Department for multiple-span bridges 
supported by bents spaced at 19-ft. intervals. This de- 
sign embodies several interesting details. As indicated 
in Fig. 19a, the design involves a variation of the chan- 
nel-shaped section. An interior unit is 6 ft. wide and is 
composed of three ribs, each approximately 9 in. wide 
and 1 ft. 4 in. deep, tied together by a.5-in. slab to give 
a total depth of 1 ft. 9 in. The 19-ft. long unit weighs 
approximately 714 tons. Each exterior deck unit con- 
sists of two ribs with a 614-in. slab and an integral curb. 
The overall width is 5 ft. 4 in. and its weight approxi- 
mates that of an intefior section. 

The bridge is supported by pile bents capped with 
reinforced concrete. Diaphragms are provided at mid- 
span and at the ends of each unit. End diaphragms ex- 
tend 3 in. below the bottom of the longitudinal ribs and 
rest directly on the supporting pile caps. Each curb unit 
is provided with two 4x8-in. drain scuppers and two 
11%-in. lifting holes. Each interior unit is cast with four 
lifting holes, one near each corner. 


Fig.18—The deck of the West 63rd St. Bridge, Miami Beach, Fla., consists of precast concrete units similar to those illustrated in Fig. 20. 


4"Std. Pipe, |'-O" lg. 


Intermediate diaphragm 


Bolts to tie units 
laterally 


a, Cutaway ViEW NEAR MIDSPAN 


5'- 4" 6'- 0" 


xB" Drain |: 
scupper; 
two per 
unit 


b. TRANSVERSE SECTION SHOWING 
INTERMEDIATE DIAPHRAGMS 


Symmetrical 
about & 


Fig. 19—Precast concrete deck units developed by 
the California State Highway Department for mul- 
tiple-short-span bridges. 


Groove for 4"pipe 


grooves extend 21% ft. on either 
side of midspan to form hollow, 
horizontal cylinders when units 
are placed side by side. Each 
cylindrical opening then holds 
one 12-in. length of standard 4- 
in. pipe located at the center of 
the span. The groove is of such 
length that shifts of the units to 
fit various skews will not prevent 
the 4-in. pipe from being placed 
at midspan. 

The precast units are provided 
with 114-in. vertical countersunk 
holes at either end and, where the 
ends of spans are to be fixed, 114- 
in. bolts are anchored into the 
pile caps. 


This design uses a fastening scheme 
whereby deck units may be bolted together 
laterally through preformed bolt holes 
even though the sections may be shifted 
longitudinally with respect to each other 
in order to fit bents skewed at certain 
angles. Exterior ribs of all units except 
those at the outside faces of the bridge deck 
are provided with six bolt holes as indicated 
in Fig. 19c. These are located so that a pair 
will line up when units are shifted to fit 
skews of 8°, 15°, 22°30’, and 30°. Fig. 19d 
illustrates this arrangement for a 30° 
skew. By relocating the holes, these units 
may also be adapted to a skew of 45° 
In all cases, bolts are passed through the 
two matching holes and are tightened 
against the faces of the ribs. 

Each unit is provided with a longitudinal, 


=== 
—— 


19'-O"c.toc. of bents 


Pier or pile cap 


at fixed ends 


c. LONGITUDINAL SECTION OF 
INTERIOR DECK UNIT 


Pier or pile cap 


semicircular groove of 414-in. diameter 
having its center of arc located 714 in. be- 
low the top surface of the slab. These 


d. ARRANGEMENT OF DECK UNITS FOR 30° SKEW 


im 


(eres for lifting 


9" Joint to be filled with 
cast-in-place concrete 


Pier or pile cap 


a. CUTAWAY VIEW AT INTERMEDIATE SUPPORT 


Cast-in-place concrete 
Key formed by |'x 4" 


10" 


Dowels at fixed ends only 


Lower form board 


b. FORMWORK FOR CAST-IN-PLACE JOINTS 


2-in. rd. anchor dowel 


at fixed ends only 55lb. smooth 


C, TRANSVERSE SECTION 


roofing paper 


d. EXPANSION JOINT AT BENTS 


Fig. 20—Bridge construction utilizing cast-in-place joints to unit precast slabs into an integral deck. 


Figure 20 


The precast construction in Fig. 20 has been used ex- 
tensively in Florida and Georgia for replacement of old, 
wornout bridges. Since repair work of this kind usually 
takes place on roadways where it is preferable that 
traffic be maintained, the use of precast units has been 
exceedingly advantageous. One-half of the bridge is 
kept open to traffic during construction, and the com- 
pleted structure is ready for use in the shortest possible 
time. 

As indicated, the design involves solid, precast con- 
crete slabs which span longitudinally between supports. 
A noteworthy feature is the longitudinal joint formed 
by placing adjacent units a short distance apart. By 
filling these joints with cast-in-place concrete, a bridge 
deck is obtained which is essentially an integral con- 
crete slab, and lateral distribution of the live load is 
achieved accordingly. 

The deck units shown in Fig. 20c are for a 20-ft. clear 
roadway and 15-ft. span, designed for H10-44 loading 
in compliance with the 1949 AASHO specifications. The 
deck is 10 in. deep and consists of four units set 9 in. 
apart. The width of interior slabs is 5 ft. and outer units 
are 4 ft. 71% in. wide, measured to the outside of the 
integral curbs. An interior element weighs approxi- 
mately 9000 lb., and a curb section about 9600 Ib. 

Before spaces between precast units are filled with 
concrete, the transverse bottom bars which extend from 
the slabs into the joints are either lapped, welded or 


12 


fastened with cable clamps. For handling, two assem- 
blies, each made up of a 7%-in. round eyebolt screwed 
into an insert, are placed in each precast slab. These 
pickup devices are located 3 ft. from the ends of the 
slabs at the center of gravity of the cross section. Holes 
remaining after the eyebolts are removed may be filled 
with mastic or joint filler which can be removed later if 
it becomes necessary to handle the units again. Two 
4-in. drain pipes are provided adjacent to the curbs in 
each 15-ft. span. 

The wide joints between adjacent units permit 
screeding out minor differences in surface levels of adja- 
cent slabs and, as a result, no additional wearing surface 
is necessary. This type of construction may be made 
continuous over intermediate supports as described on 
page 18. 

The handling and erection procedures involve no new 
techniques. Work progresses from one end of the bridge 
to the other as the crane operates on spans already 
erected. Under favorable conditions, the hoisting equip- 
ment may operate directly from the stream bed. 

The 5-ft. wide slabs with squared ends may be placed 
on piers that deviate up to 10° on either side of a 
line perpendicular to the bridge axis. This angle of 
deviation is based on a variation in bearing of from 4 in. 
to 16 in. on a 20-in. wide support. By tapering the ends 
of the slab, greater angles of skew can be met. An ad- 
vantageous feature is that such a precast slab can be 
used over a fairly wide range of angles of skew. 


Units of this type may be handled as shown in Fig. 8. 
These are designed for a 25-ft. span and are 5 [t. wide, 
18 in. deep and weigh approximately 28,000 Ib. 


Figure 21 

In selecting a type of precast concrete bridge con- 
struction, it is important to consider the weight of in- 
dividual elements, since use of light units facilitates 
handling and erection. Fig. 21 illustrates a design de- 
veloped by the Nebraska State Highway Department 
in which the individual slabs are formed to provide a 
reduction in dead weight. Each unit has two cylindrical 
hollow cores which extend through its entire length 
and which cause approximate reductions of 35 per cent 
in the cross-sectional area but only 10 per cent in the 
moment of inertia of the concrete section. 

The details presented are for a bridge having a span 
of 16 ft. from center to center of supports and a roadway 
width of 20 ft. from curb to curb. The design is based 
on H15-44 loading. The deck consists of seven precast 
units, each | ft. 624 in. deep. The two outside units are 
3 ft. 3 in. wide and the five interior units are each 3 ft. 
wide. The hollow cells may be formed with flexible, 
collapsible tubing or with stiff metal mandrels well 
greased or protected by paper wrapping. In the latter 
case the cells vary in diameter from 12 in. at the ends 
to 11 in. at midspan. 

Shear keys are provided at adjacent longitudinal 
faces of the slabs, and the design calls for three 1-in. 
tierods inserted through transverse pipe sleeves and 
tightened at the outside faces of the deck so as to press 
the individual slabs together and assist tae shear keys 
in the lateral distribution of superimposed loads. One of 
these rods is located at midspan and the other two ap- 
proximately 6 ft. on either side of midspan. That portion 
of the longitudinal slab face which is below the shear 
key has a tolerance not exceeding 1% in. and is coated 
with mastic paint. An interior unit weighs approximate- 
ly 7300 Ib. 

The abutments consist of piles capped with reinforced 
concrete. Dowels extending vertically from the pile caps 
are welded to bars extending horizontally from the 
precast slabs and the bars are finally embedded in con- 
crete as shown in Fig. 21c. The hollow cores are plugged 
at their ends by cups of heavy paper or thin sheet metal. 
The cast-in-place concrete on top of the pile caps closes 
off the open cores and, if adequately reinforced, also 
serves as a lateral tie to hold the various deck units to- 
gether. Such a tie may eliminate the necessity for all 
but midspan tierods. The detail shown for an end sup- 
port may be applied to an intermediate support. Spans 
may then be designed either on the assumption of sim- 
ple supports or for continuity as discussed on page 18. 

In considering the lateral distribution of superim- 
posed loads, the most conservative design viewpoint is 
to assume that each unit carries 14-lane loading. The 


Precast concrete curb> 
/ 


Precast concrete recast unite 


yShear key to be 
/\ vi filled with mortar 


l-in. rd. tierod 
Paint with mastic 


VETO LITEM 
Anchor bolts 


a Cutaway View OF DECK UNITS 


g" re 


i AN |5-in. rd sleeve 


Mortor 


ol 


VARY _\ ogre aeV 


connection 


Swedge bolts =o! | =" J o* | a | i'- 6" cea 
for post rid ; 


b. TRANSVERSE SECTION 


ry a Metal or paper plug 
Weld straight bars — 


from precast slab 
to dowels from 


Hollow core 
Precast slab 
Cast-in-place concrete 


= ’ 
“—~—Pier or pile cap 


16-0" c.toc. pile caps 


c. LONGITUDINAL SECTION NEAR SUPPORT 


Fig. 21—Hollow-core precast units form this bridge deck. 


seven deck units indicated here would then be designed 
to carry a total of 314% lanes which is 75 per cent more 
than the two lanes the bridge actually carries. If full 
lateral distribution of the load is assumed, each unit 
may be designed to carry 2/7 of one lane loading. This 
ideal condition may be attained by a proper selection 
of details serving to transfer the shear laterally and to 
hold the individual units together. 


ia} 


$-in. rd plain bar 


for linkage 


-Precast deck slab 
Opening in precast curb Shear key 


to receive mortar 


Nailing block for 


Joint filled with pre- 
Sea concrete 


fastening joint 


p 
filler AP 
ALES: ol 
a a L/7 
Wh 
ee g Steel bearing 
~ Diaphragm plate—~ 


Shear key to be filled 
with pre-shrunk mortar 


Za 


“Pile cap notched to provide crown 


a. CUTAWAY VIEW AT INTERMEDIATE SUPPORT 


—Precast slab : 
Expansion End 
‘Precast beam : ' ; 
a ' i) ry 
“Fixed End | 84 Seis oe 


25-0" c.toc all interior spans 


C. LONGITUDINAL SECTION 


Fig. 22—Precast beams and slabs are united 
by cast-in-place joints to form the bridge super- 
structure. 


Figures 22-24 


The precast concrete bridge illustrated in Fig. 22 is a 
modification of the design used for the Baker River 
Bridge in Washington. The design is for a 26-ft. roadway 
and for a repeated number of 25-ft. spans supported by 
pile bents. The design follows the H20-S16-44 loading of 
the 1944 AASHO specifications, and allowable stresses 
are 20,000 psi in the reinforcing steel and 1100 psi in the 
extreme concrete fibers in compression. The superstruc- 
ture is entirely precast with the exception of the con- 
crete required in the joints to join the component parts 
into an integral unit. Pile caps are notched to provide 
a 114-in. crown on the road surface. 

Precast beams are designed as simply supported, 


14 


Slab thickened for 
transfer of wheel loads 


b. DETAIL AT UNSUPPORTED TRANSVERSE 
EDGE OF SLAB 


cl Premolded joint 
filler nailed to 


3 mortar joint between 
curb sections 


toy len 

5 

& 

1a WLLL IW, 
a SRSA SSS 


Kole 


oO 
aL @. 
N . 
Expansion Fixed i 
end 
2a 


14°x2'ki-4"R 
l-in. rd. dowel 


8-4" c.toc. 


d. CROSS SECTION SHOWING TRANSVERSE JOINTS 


rectangular beams for dead load and as T-beams for 
live load. Continuity of the stringers over intermediate 
supports may be obtained as discussed on page 18. 
These beam units weigh approximately 6300 lb. each 
and are 10 in. wide, 2 ft. deep and 24 ft. 11 in. long. 
A l-in. clear space is allowed between end faces of all 
beams. Shear keys are provided both at the tops of the 
beams and at the sides of the slabs to insure maximum 
effectiveness of T-beam action and, in addition, the 
cast-in-place concrete in the joints is reworked without 
the addition of water just prior to its initial set to pre- 
vent a separation due to shrinkage. The ends of beams 
which are to be allowed to move during expansion and 
contraction are fitted with steel plates at the bottom 


which match bearing plates at the top of the pile cap. 
Beam ends which are to remain fixed are cast with a 
2-in. dia. hole 334 in. from the end. An 18-in. dowel 
passes through this hole and through a similar hole in 
the bearing plate and penetrates 9 in. into the pile cap. 
The hole is then grouted. 


Between any two beams, one span of the deck con- 
sists of three precast slabs, each approximately 8 ft. 
4 in. long, 4 ft. 21% in. wide, and 6 in. deep. At the two 
intermediate transverse joints between pile caps, the 
6-in. depth of these slabs is thickened to 8 in. for a 
distance of 15 in. on either side of the joint, and slabs 
are made so that the abutting faces at these joints form 
a circular shear key as shown in Fig. 22b. The thickened 
slab and the shear key are intended to provide for 
transfer of wheel loads at these unsupported edges 
without the use of beams or diaphragms. The shear keys 
are filled with preshrunk mortar after units are in their 
final position. 


Diaphragms cast integrally with the slabs meet over 
the supports and are separated by premolded joint filler 
fastened to nailing blocks embedded in the exterior face 
of each diaphragm. These diaphragms are 8 in. thick and 
extend 12 in. below the slab. The diaphragms and the 
thickened portion of intermediate panel edges fit into 
the clear space between adjacent beams with 1%-in. 
clearance. The 6-in. deck panels are 31% in. wider than 
the clear space between adjacent beams so that a 1°%- 
in. seat is provided. 


Deck slabs are designed as simple spans between 
beams for both dead and live loads although some con- 
tinuity will be developed by the interlocking of the slab 
and beam reinforcement in the cast-in-place joint. Deck 
units weigh approximately 3100 lb. each. 


Precast units are handled by the reinforcement pro- 
truding from the tops of the beams and sides of the 
slabs as shown in Fig. 10. By using precast beams, curbs 
discussed on page 19 and slabs with integral dia- 
phragms, the amount of cast-in-place concrete is small 
and erection rapid. A mobile crane can complete the 
erection of the first span and then operate on the deck 
to erect additional spans progressively across the bridge. 
By this procedure a small crew working a single shift 
erected one span of the superstructure in one day. Al- 
though a bituminous surface was contemplated for the 
Baker River Bridge, the riding qualities of the resulting 
roadway were so satisfactory that the surfacing was not 
placed. The completed structure is shown in Fig. 23. 


Fig. 24 and the cover illustration show the erection 
of a bridge in Spokane County, Wash., some features 
of which are similar to the design used for the Baker 
River Bridge. Here, haunches on the 30-ft. 7400-lb. 
beams support the deck slabs. Precast slabs are 5 ft. 
91gin. by 15 ft., by 51% in. thick and weigh 6000 Ib. 


Fig. 23—The deck of the Baker River Bridge in Washington is 
composed of precast slabs and precast beams integrated by 
cast-in-place longitudinal joints. 


Fig. 24—The erection of a bridge of precast beams and slabs 
with cast-in-place joints in Spokane County, Wash. 


Cast-in-place deck 
slab with Iz crown 


"mortar & a 
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ie po tk tL 


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Top of pile cap sloped 
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iE 


Fig. 25—Bridge construction in- 
volving precast beams and cast- 
in-place deck slab. Formwork for 
slab is supported by the beams. 


Figures 25-28 


Fig. 25 illustrates a semiprecast construction with 
precast beams and a cast-in-place deck slab and curb. 
Although this type of construction requires placing con- 
crete in the field, the formwork is supported entirely by 
the precast beams, and no falsework is required at the 
erection site. 

The details presented here were prepared for a bridge 
constructed in Clark County, Wash., having two 20-ft. 
spans and a roadway width of 22 ft. between curbs. The 
H15-S12-44 design load was specified with allowable 
stress of 18,000 psi in the steel reinforcement and re- 
quired compressive strength of 3000 psi at 28 days for 
the concrete. The bridge superstructure is supported 
by conventional foundations including reinforced con- 
crete abutments and a center pier of piles capped with 
reinforced concrete. The bridge seats provide a 114-in. 
crown at the centerline of the roadway. 

Precast beams are 9 in. wide, 16 in. deep and 20 ft. 
5 in. long and are designed for two loading conditions. 
First, the girders are designed as simply supported 
rectangular beams to carry their own weight, the dead 
weight of the deck formwork and the weight of the 
fresh concrete for the roadway slab; and second, since 
they are considered to act integrally with the cast-in- 
place deck slab, the girders are designed as T-beams for 
carrying the live loads. Shear keys are provided in the 
top surfaces of the beams as shown in Fig. 25a to assist 
in producing the integral action. These keys may be 
formed by small precast concrete block spaced at short 


16 


3" Sheathing — 
2°x4'x2-Il"@ 16 ctoc 


ane where 
necessary 


b. DETAILS FOR SLAB FORMWORK 


intervals along the top surfaces of the beams and 
depressed to one-half their depth before the concrete 
hardens. Continuity over intermediate supports may be 
secured as discussed on page 18. 

Beams are precast in wood forms similar. to those 
shown in Fig. 3, and weigh 3000 lb. each. To vary the 
beam lengths, a movable bulkhead is provided, and a 
movable soffit form at the bottom provides a means for 
changing beam depths. 

Fig. 25b indicates how formwork for the 6-in. deck 
slab is supported by the precast beams. Ledgers made 
of 2x4’s are bolted to each side of the stringers through 
horizontal pipes set 934 in. above the bottom of the 
beams and spaced at 16-in. intervals. Transverse 2x4’s, 
also spaced every 16 in., then span between these ledgers 
to support the 34-in. sheathing on which the concrete 


is placed. Formwork is also prepared for 6-in. thick 
diaphragms located at each end of the spans. All deck 
forms are laid upon their supports without nailing, and 
no fastening of sheathing is required other than that 
necessary for the special construction at the ends of the 
bridge to insure proper connection to the abutment 
seats. 


Cast-in-place deck slab 


Precost beam 


Fig. 26—Composite precast beam and cast-in-place deck 
slab construction used in Lowell, Mass. 


Fig. 26 is a partial cross-sectional view of a construc- 
tion system involving precast girders and a cast-in-place 
deck slab which has been used in Lowell, Mass. The 
general design features here are similar to those described 
for the bridge in Clark County, Wash., except that the 
deck formwork is supported by 15-in. wide shelves 
located near the bottom and on both sides of the girders. 
Units having the cross-section shown in Fig. 26 were 
52 ft. long and weighed 12 tons each. They were pre- 


"Sheathing 


au Wire hanger 


Fig. 27—Precast concrete joist supporting formwork for a cast-in- 
place deck slab. 


cast 65 miles from the erection site and transported to 
the bridge by a tractor-trailer rig. (See Fig. 7.) 

Fig. 27 shows in cross-section a third type of precast 
beam used in bridges subjected to light traffic loads. 
This sketch also indicates another method of supporting 
formwork for a cast-in-place deck. 

The shape of this unit is similar to that made by many 


aa? 


Fig. 28—Precast concrete beams illustrated in Fig. 26 support 
formwork for a cast-in-place deck slab in Lowell, Mass. 


concrete products manufacturers for reinforced con- 
crete floor joists used in building construction. This sug- 
gests the possibility that these manufacturers may, 
with minor changes, produce precast beams suitable for 
carrying the heavier bridge loads. The opportunity to 
obtain ready-made beams will eliminate precasting 
operations in the field and will reduce bridge erection to 
setting the joists into position and casting the deck 
slab over them. 


Figure 29 


The details of Figs. 29a and 29b were developed by 
the California State Highway Department and may be 
useful when an existing bridge superstructure is replaced 
by one composed of precast concrete elements. This 


LEG 


Channel-shaped precast 
deck units 


|-in. rd. holes 


oe. 


Joint filler 


. 
<a 
2 Dowels placed & Pier or pile cap 
cece rea 
one "+ a 
9" g" wl [20% 


b. SECTION A-A AT SUPPORT 


Fig. 29—Deck units designed for narrow pile caps. 


construction is intended to overcome the difficulties of 


supporting units from adjacent spans on a narrow pier 
or pile cap. Although the details shown are for use with 
channel-shaped deck units, they may be modified for 
application to other types of precast construction. 


Continuity in Precast Bridges 


Continuity may be used over intermediate supports 
and at abutments when it is desired to eliminate trans- 
verse joints or to reduce midspan bending moments. 
Continuous construction reduces deflections under live 
load by as much as 89 per cent of those occurring in 
simple spans and provides an even road surface. 

Precast units which support loads in a continuous 


18 


Gast-in-place concrete 
for continuous joint 


Precast unit 


Fig. 30—Temporary shoring reduces stresses in precast bridge 
units before continuity is effected at the supports. 


structure should be designed as simple spans for dead 
load and as continuous spans to carry the live loads. 
Depending upon the type of construction involved, the 
dead load may be of considerable magnitude during 
erection. It may not only be the weight of the unit itself 
but also may include the weight of formwork for a cast- 
in-place deck slab, of construction equipment and of 
the freshly cast concrete. Under these circumstances, it 
may be advantageous during erection to use temporary 
shoring and thereby decrease erection stresses. Fig. 30 
illustrates one way to accomplish this. Temporary 
shoring is supported by ledges at the piers or abutment 
bases as shown and negative bending stresses at mid- 
span are counteracted when the unit is in place and sup- 
ports are removed. If stream bed conditions are satis- 
factory, temporary piling may be placed so as to reduce 


-Precast unit Lap bars in 
Cast-in-place concrete cast-in-place 
Field weld concrete 


Premolded 
joint filler 


-Lapped splice 
Cast-in-place concrete 
Precast unit 


Cast-in-place concrete 
Precast unit 


Lap or weld 
in field 


Fig. 31—Suggested methods for achieving continuity at interior 
supports (a-c) and at abutments (d). 


dead load stresses to the degree desired. The location of 
all temporary supports should be indicated on the plans. 

The manner in which individual elements are joined 
to produce continuity may vary with the type of pre- 
cast construction used. A few suggested methods are 
illustrated in Figs. 3la through 31d. The connections 
shown are intended for elements which carry the loads 
to the piers or abutments. Depending upon the class of 
bridge selected, these elements may be the longitudinal 
precast beams which support precast deck slabs as 
illustrated by Fig. 22, the T-beams formed by adjacent 
ribs of precast channel-shaped sections as shown in 
Figs. 15 through 17, the T-beam of Fig. 14 or the solid 
or hollow core slabs shown in Figs. 13, 20 and 21. In 
every case, the length of the lap or weld should be suf- 
ficient to develop the full strength of the reinforcing 
steel. 

With solid or hollow core slabs, the splicing of the 
main reinforcing steel will be a continuous operation 
over the length of the transverse deck joints, whereas 
with longitudinal beams splicing will be required only in 
the vicinity of these beams. However, to help prevent 
cracks in the transverse joints between spans it may be 
advisable to precast the deck units with longitudinal 
steel protruding from the edges of the slabs as well as 
from the beams, and to splice this steel even though it 
theoretically carries no load. This detail will assist in 
producing an integral concrete structure. 

The construction illustrated by Fig. 13a utilizes the 
abutting units at transverse joints to form holes for 
tierods. Although the separation of the units at the sup- 
port to allow for splicing of top reinforcement will 
eliminate this detail, the entire deck may be tied later- 


ally by reinforcing rods set into the transverse joints 
before these joints are filled with concrete. As an alter- 
nate method, the detail shown in Fig. 32 may be used. 
Matching vertical holes in the pier and in the precast 
units receive dowels. 


Lapped splice 


Hole to receive 
transverse tierod 


Fig. 32—Continuous joint with 
provision for transverse tierod. 


The construction shown in Fig. 25, involving precast 
beams topped with a cast-in-place deck slab, may be 
provided with continuity over the intermediate sup- 
ports merely by inclusion of a sufficient amount of top 
reinforcement over the supports in the cast-in-place 
slab. 

Fig. 31d illustrates one method for obtaining con- 
tinuity at an abutment. Vertical holes may be cast or 
drilled in the abutment to receive dowels, or in new 
construction the dowels may be set into position when 
the abutments are cast. The field connection merely 
requires a proper splice either by lapping the rods as 
shown or by welding. The bars are then enclosed in 
cast-in-place concrete. 


MISCELLANEOUS DETAILS 


Curbs and Handrails 

The location and erection schedule for a bridge com- 
posed of a precast concrete deck frequently make the 
added use of precast concrete curbs and handrails ad- 
vantageous. Some precast concrete bridge decks have 
been designed with precast curbs made in one piece 
with the outside deck members. Among these designs 
are those illustrated in Figs. 13, 16, 17 and 20. Although 
such construction is excellent for certain conditions, it 
is also possible and in many cases advantageous to pre- 
cast the curbs separately in lengths short enough for 
easy handling. Fig. 21 illustrates a curb which is sepa- 
rated from the precast deck unit by precast concrete 
shims. Both the curb and shims have a height of 6 in. 
so that the curb top is 12 in. above the road surface, 


leaving open slots approximately 41% ft. long between 
the shims. This design aids in keeping the roadway free 
of dirt, leaves, snow and other debris. 

Figs. 22a and 33 illustrate a precast curb made in- 
tegral with the deck by using a small amount of mortar 
at the erection site. The curb is formed with intermit- 
tent interior hollow spaces as indicated. Stirrups pro- 
truding from the top surface of the outside beam inter- 
lock with the horizontal deck slab reinforcement in the 
void formed between the beam, slab and curb. Mortar 
placed through openings in the curb then ties the three 
parts together into one unit. 

A third variation involves a precast curb which may 
be bolted to the precast deck. Contacting surfaces may 
be separated by a thin layer of mortar. 


19 


Notch to be filled with 
C mortar or mastic 


Bolts to fasten post 


SECTION A-A 
(Shows Curb Unit Only) 


i sla he 


rue 


Note: i 
Fill openings with A 


cast-in-place mortar 


SECTION C-C 


Fig. 33—Curb and handrail details for the precast concrete 
bridge illustrated in Fig. 22. 


Fig. 14 illustrates a cast-in-place curb tied to the 
precast deck by alternate beam stirrups which protrude 
above the deck. 

The attachment of handrails to precast superstruc- 
tures may be accomplished in many ways, and some 
of the methods which have been used are illustrated. 
Fig. 14 shows one instance where precast concrete posts 
are fastened to a composite construction consisting of 
cast-in-place curbs and precast T-beams. The steel 
channel section serves to secure the ends of the trans- 


PRINTED IN U.S.A. 


verse tierods and also to hold the lower supporting bolt 
for the post. The upper post support is the bolt which 
is set in position along with the cast-in-place curbing. 

Precast concrete posts may be used with the construc- 


Precast concrete 
post 8'x7" 


Fig. 34—Handrail for precast con- 
crete bridge illustrated in Fig. 20. 


tion shown in Fig. 20 as illustrated in Fig. 34. U-shaped 
dowels with threaded ends are set in place when ex- 
terior deck slab units are precast, with the result that in 
the field the handrail posts may be quickly bolted into 
position. 

Fig. 21b and Fig. 33 illustrate two methods whereby 
posts may be attached to bridge decks utilizing curbs 
which are precast as separate units. The former involves 
attachment to both the deck and the curb, whereas the 
post in the latter case is supported entirely by the curb. 


Fig. 35—Precast handrail posts are bolted to ex- 
terior deck units of a precast concrete bridge near 
Humphrey, Nebr. Transverse tierods extend 
through plate washers and are tightened against 
outer bridge faces. 


The drawings in this publication are typical designs and 
should not be used as working drawings. They are intended 
to be helpful in the preparation of complete plans which 


should be adapted to local conditions and should conform 
with legal requirements. Working drawings should be pre- 
pared and approved by a qualified engineer or architect. 


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Introduction 


ae concrete panels are used in curtain wall con- 
struction because they can be installed rapidly and 
will result in a weathertight, durable wall. Fast erection 
reduces overall cost by allowing early occupancy of the 
building. Concrete meets the requirements of resistance 
to wind, rain and fire at low initial cost and with mini- 
mum annual maintenance. As in other types of concrete 
construction, precast concrete wall panels lend them- 
selves well to pleasing architectural expression. 

This booklet presents a number of types of precast 
concrete curtain wall panels. Not included are precast 
wall units made integral with the structural frame, such 
as the tilt-up wall panel* and the precast, load-bearing 
interior and exterior wall. 

Precast concrete wall panels attached to structural 
frames may be classified by their cross-section, e.g., the 


solid panel, the insulated or “sandwich” panel, and the 
ribbed or “‘thin-wall” panel. They may be fabricated at 
plants of concrete products manufacturers, in temporary 
casting yards at the jobsite, or on the floors of the build- 
ing which they are to enclose. 

When designing wall panels engineers and architects 
must consider such factors as fabrication and form design, 
tolerances, handling and transportation, erection, con- 
nections and inserts, joints, materials and textures. So- 
lutions often depend on conditions which vary for dif- 
ferent projects. In this booklet individual constructions 
are described together with some suggested and promis- 
ing modifications of these designs. 


*See Tilt-up Construction, available free in the United States 
and Canada upon request to Portland Cement Association. 


Development 


‘Thee concept of building with prefabricated concrete 
elements, made under plant conditions that are more 
favorable than are usually found on the job, has only 
recently been put to general use. Precast concrete wall 
panels of the type included here have shown particular 
progress in the last decade. Briefly, two developments 
have brought this about—general availability of mobile 
equipment to handle the precast units, and materials and 
methods to produce durable and strong precast concrete 
units in a minimum of time. 
Some examples of precast concrete wall panels have 
appeared in earlier years. One such panel type (Fig. 1, 


Front Cover. This close-up of a precast concrete, insulated 
wall panel shows the deep, straight grooves of a broomed 
finish and the contrasting, even joints. Specified joint width 


is Ye in. and the edges are beveled. The bevel reduces 
tendency for the edges to chip during handling and im- 
proves appearance. A black calking material seals the 
joint and emphasizes the pattern in the finished wall. 


page 4), developed before 1910 principally for low-cost 
housing, is still being produced in a plant near New York 
City under rigid material controls and using assembly- 
line techniques. Basically it is a thin-wall type of panel 
although the hollow cores give it thermal properties 
similar to those of the sandwich panel. 

The E. I. duPont de Nemours Company was one of the 
early users of precast concrete wall panels. An investiga- 
tion was made in 1946 by their engineering department 
to select for new industrial plants the most satisfactory 
wall type ‘“‘which would give maximum coverage in mini- 
mum time with the most efficient use of field labor.”’* 
A precast concrete panel with a core of filler block was 
selected because it most nearly met the requirements 
determined by their study: 

1. Materials should be simple and readily available 

locally; 

2. Fabrication and erection operations should be 

simple; 

3. Formwork should be a minimum with maximum 

number of re-uses; 

*Civil Engineering, September 1948. 


COPYRIGHT 1954 BY PORTLAND CEMENT ASSOCIATION 


Concrete column 
Floor slab 


Spandrel beam 


ne Angie with split leg if 


bolted to concrete f 


Foundation wall 


Fig. 1. These hollow wall panels, made in special machines, are 
cast and cured in a vertical position. The units come in standard 
widths and heights and are attached easily and quickly to struc- 
tural framing. The smooth interior finish of the panels may be left 
exposed or painted. 


4. Horizontal casting should be adopted for better and 
easier surface treatments and finishes; and 

5. A self-aligning joint should be used to speed erection. 

Details of the panel adopted by the duPont Company 
are shown in Fig. 2. One of the factory buildings near 
Chattanooga, Tenn., built with this precast sandwich wall 
panel, is pictured on the inside front cover, lower left. 

About the time the duPont Company was making its 
investigations, a glass company was planning a combined 
store and warehouse in Canada. The owner and architect 
wanted a building well insulated to withstand the severe 
winter climate. At that time a precast insulated wall 
panel consisting of a layer of lightweight vermiculite con- 
crete sandwiched between two layers of normal weight 
concrete was being developed in Toronto. Substituting a 
product of their own industry for the center layer, a 2-in. 
thick insulating block of cellular glass between 114-in. 
layers of concrete resulted in a panel with the low heat 


4 


Perimeter reinforcing bar 

Anchor insert for 
holding bolt 
Threaded washer 


Holding lug welded 


to structural frame sket 


insert 


ire mesh reinforcement 
Cored gypsum filler block 


Gasket 
Shelf angle at each 
end of panel 
Structural column 


Fig. 2. A typical precast sandwich wall panel for the duPont 
Company nylon plant near Chattanooga, Tenn., is 80 sq.ft. in 
area, 7 in. thick and weighs slightly more than 22 tons. This panel 
has a low heat transmission coefficient of 0.24* and a tentative 
3-hour fire rating as determined by the company’s Safety and 
Fire Protection Division. The tongue-and-groove joint is self-align- 
ing and is made weathertight with a plastic, bituminous gasket, an 
asbestos rope packing and calking material. The panels were 
bolted to the steel frame, saving an estimated two-months’ con- 
struction time in enclosing the buildings. Wall panels were site- 
produced on a 24-hour casting cycle. 


transmission coefficient of 0.16.* The wall panels, with 
glass block windows in place, were fabricated on the 
floor of the building. Each unit was 6 ft. 8 in. wide by 
17 ft. 6 in. high, tilted into position, and attached to the 
reinforced concrete frame. The joint detail in Fig. 3 shows 
that the panels provide a continuous barrier against heat 
loss. 

Another wall study was started in 1948 in connection 
with a metals plant for the Electro Metallurgical Division 
of Union Carbide and Carbon Corporation. The initial 
aim was to find a satisfactory type of wall to enclose the 
steel framework of a 160,000 kw. powerhouse. A sand- 
wich panel consisting of two 134-in. outer layers of con- 
crete and an insulation layer 1% in. thick of chemically 
treated wood chips held together with a cement binder 
was used. The heat transmission coefficient of these 
panels was 0.32.* 

A study was also made of the most desirable panel 
size. Large panels reduce the number of joints but are 
more difficult to handle and more costly to transport. 
Since it was planned to make the panels in a factory, 


*Btu per hour per square foot per degree Fahrenheit (see 
page 14). 


transportation cost became an important factor. An 8-ft. 
square panel was selected because it is easily handled in 
production and transportation, not too many joints are 
required, and shrinkage is uniform in both directions. 
A tongue-and-groove joint (see Fig. 9, page 8) was 
adopted which was weathertight and self-aligning. The 
completed power plant is pictured inside the front cover. 
Other buildings of this large industrial plant built sub- 
sequently were enclosed with precast sandwich wall 
panels of similar design but having a different insulation 
material. 

Furring and plastering the inside face of a solid panel 
for insulation is considered undesirable for an industrial 
building. Where insulation is not significant or can be 
gained by other than built-in materials, the solid panel 
gives a satisfactory wall, functionally and aesthetically. 


2'Cellular glass insulation 
it Concrete 


Calking compound 


See 


b> ofU be 


Cementitious asphalt mix 


Fig. 3. Joints between sandwich wall panels on the combined ware- 
house and store for Hobbs Glass Co., Three Rivers, Quebec, pro- 
vide a continuous layer of insulation. The inside surfaces of the 
panels were cast on canvas to give a finish easily painted without 
other treatment. This building became a “pilot model” for other 
precast concrete sandwich panel projects in various sections of 
Canada. Although experimental in nature the sandwich wall com- 
pared favorably in cost and performance with 12- and 14-in. 
walls furred with lath and plaster. 


Panel Attachment 


Jie precast curtain wall generally is affixed to the 
outside of the structural frame and thus the panel 
sizes need not be built to fit the column spacings. In- 
stead, panels are designed to obtain the most suitable 
conditions of fabrication, handling and erection. Rela- 
tively simple methods of attachment permit rapid erec- 
tion. The connections used, as well as the panels, must 
meet the fire resistance requirements of building codes. 
Another consideration is that insulation must be detailed 
so as to avoid cold zones in the outside walls. 
An unusual combination of concrete frame and pre- 
cast solid panels of lightweight aggregate concrete was 


Fig. 4. Three 200x600-ft. warehouses for the Navy at Great Lakes, 
Iil., are built with thin-wall, ribbed wall- and roof-panels which 
span 22 ft. 6 in. between precast concrete frames. These panels 
were cast on concrete molds in a yard near the site, removed 
with vacuum lifters after 20 hours and installed 3 to 4 days later. 
All panels are attached to the frames by welded, matched insert 
plates. The wall panels were set on mortar beds which were raked 
out on the outside face, later to be calked. 


Problems of attaching and joining precast panels, whether 
solid or sandwich, are the same. 

Thin-wall, ribbed panels have been used in a number 
of Navy buildings. Three large warehouses at the Naval 
Training Station, Great Lakes, IIl., have walls and roofs 
built of 5-ft. wide, ribbed panels. The panels have a 
minimum thickness of 1144 in. and span between precast 
rigid frames. To help maintain an inside temperature 
above a specified minimum, insulation was sprayed on 
the thin portion of the wall panels. Fig. 4 is an interior 
view of one of these warehouses. 


to Concrete Frames 


used in the 6-story, 550 Building in Miami, Fla. Flat plate 
floors are cantilevered to the outside walls and exterior 
columns are eliminated. Story-height precast panels are 
hung from the slab edge and overlap the panels below as 
shown in Fig. 5. 

The panel connections (Fig. 5) are simple and fire- 
proofed. Slotted anchor plates allow necessary adjust- 
ment for alignment. Joints between panels are sealed with 
an aluminum backing strip for the calking compound. 
The metal strip which is sprung into position in the 
groove is similar to slats in venetian blinds. The outer 
portion of the joint remains open giving a pleasing 


5 


Fig. 5. The 550 Building, Miami, Fla., is enclosed with 4-in. precast 
concrete panels in such a manner as to make the panel module 
independent of the column spacing. All anchorages are adjustable 
and protected by the terrazzo floor topping. A typical panel is 
11 ft. 5 in, high and 7 ft. 1% in. wide and is designed to resist 
winds of hurricane force. Panels are made with lightweight concrete 
to reduce dead load—an important advantage since they are 
hung from cantilevered floor edges. The exterior surface of white 
quartz aggregate in white cement is highly weather resistant and 
requires little or no maintenance. 


shadow effect. Horizontal joints are eliminated thus sav- 
ing material and labor. 

These panels were precast in a concrete products plant 
where quality control and careful casting produced uni- 
form units with minimum loss due to damage or break- 
age. White quartz aggregate concrete made with white 
portland cement on the outer face presents an attractive 
surface. 

Curtain wall panels are sometimes placed between 
columns and spandrel beams. The feed mill and the 
apartment building on the inside front cover show this 
arrangement. The solid panels of the feed mill were pre- 
cast on the ground floor and installed from the inside. 
The fastening detail (Fig. 6) consists of a lip in the cast- 


4' Precast concrete 
wall panel 


a _—6'x6"+6/6 Wire mesh 


Cast-in-place 
spandrel beam 


Embedded 
anchor bolt 


Bent metal 
anchor strap 


Precast panel 


2x 3" Slots filled with concrete 
when panels are in place 


Slotted metal inserts 


Threaded metal inserts 


Anchor bolts in wall 
panel below 


Floor slab 
Window opening 


Precast reinforced 
lightweight con- 
crete wall panels 


Anchor bolts cut 
short after instal 


Notes Tempered 
aluminum strip 


DETAIL C 


Tile facing 
Slotted hole 
Terrazzo 


5 > Bolt 
Metal insert 
5 Metal 
insert ++Metal clip 
of Precast wall 
panels with 


quartz aggregate 
surface 


4" 3° Anchor bolt 


DETAIL A DETAIL B 


Concrete slab 
Wire mesh 
reinforcement 


Fig. 6. Precast wall panels on the 5-story Merchants Company 
feed mill at Vicksburg, Miss., are of two types—floor-to-floor 
smooth-faced panels and corrugated sill panels. The anchorage 
arrangement does not require accurate positioning of inserts in 
the cast-in-place concrete frame. Narrow panel width and light- 
weight concrete made it practical to handle these pieces from 
inside the building with a fork-lift truck. A casting tolerance was 
maintained to give a uniform %-in. joint. 


wv 


Concrete 
floor 


Drip 


5' Precast bearing 
partition panel 

*4 Hairpin reinforcement 
cast in partition 


Cast-in-place 
window sill 


55 Precast 
concrete 


Rigid 
insulation 
Watertight 


at joint sealer 
Precast concrete joists J 


a 


Fig. 7. A proposed type of precast concrete wall panel which 
satisfies insulation and firesafety requirements is shown for use 
with continuous windows. The dovetail anchor slot is used to hold 
the panels in place until they are anchored at the floor slab. 
Additional anchorage is obtained by welding matched insert 
plates in the exterior and partition panels. A suggested applica- 
tion of this wall panel is given in the architectural rendering of an 
apartment building on the back cover. 


Fig. 8. This proposed insulated precast concrete panel for multi- 
story apartment buildings is designed for quick and easy installa- 
tion. Careful attention to the joint details, especially the horizontal 
joints, makes erection of the wall panels easier and faster. A rigid 
filler or seal, such as sponge rubber, is glued in the joint grooves 
before the panels are erected. Later oakum and calking material 
can be packed into the joint from a hanging scaffold or bosun’s 
chair. 


in-place spandrel beam, which prevents the panel from 
moving outward, and a metal clip to hold the panel in 
place. At the base a recess is cast in the floor to receive 
the panel. 

The apartment building on the inside front cover also 
has solid precast concrete wall panels cast on the floors. 
A modification of this panel design is shown in Fig. 7. 
Particularly adaptable to apartments, it can be used as 


Tongue and groove joint 
Concrete floor 


Vertical reinforcement 
Expanded metal ties 
Rigid insulation 


4'x 35 
Support angl 


Spandrel beam 


Hanger angle with slotted 
hole and *3 bar for lifting 


Precast concrete 
insulated panel 


Hanger angle, 
2 @ bolt and lifting 
loop bent over 


Spandrel beam 


5 Joint: eee 


8 


Rigid filler 3" Adjustable insert 
Oakum eee 
Calking 4x35 support angle 


DETAIL OF HANGER 


well for hospitals and dormitories. The floors are sup- 
ported on precast concrete interior partitions. The ex- 
terior precast panels are sill high and supported on the 
small spandrel beam formed with the outside joist. 
Windows are continuous, an architectural feature gaining 
in popularity. The panels under the windows are backed 
up with concrete masonry. The panels cover and insulate 
the spandrel beam, thus preventing cold zones or areas 


fi) 


of condensation. Concrete ceilings can be left exposed. 

A curtain wall of insulated, precast concrete panels, 
developed for attachment to building frames of rein- 
forced concrete, is shown in Fig. 8. This wall was designed 
to develop adequate resistance to a 30-psf wind or suc- 
tion load, obtain a 2-hour fire rating for panels and con- 
nections, require the minimum number of different panel 
sizes, simplify connections and reduce installation costs. 

Between windows the standard size panel is one story 
high with the top edge level with the bottom of the 


Panel Attachment 


Pe concrete wall panels have been used on many 

steel-framed industrial buildings. Rapid enclosure 
and overall economy are particular requirements which 
can be met readily with such panels. In addition, the 
appearance is in keeping with modern trends in indus- 
trial building design. 


Malleable iron clamp 
Lead sheet under clamp 
Bolt insert in panel 
3'Bolt 


Channel support 


4 
SN 
| Continuous angle support 
Mepee every third panel 


spandrel beams. The sill panels vary in height. Panel 
widths are independent of column spacings and are 
selected for convenience in casting and handling. 

The hanger support and tongue-and-groove joint give 
correct alignment quickly. Supporting angles are secured 
to adjustable inserts in the cast-in-place spandrel beams, 
which allows for minor variations in the height of the 
panels. Metal connections are protected above by grout- 
ing the space between spandrel beam and wall panel, and 
below by plaster at the spandrel beam soffit. 


to Steel Frames 


The Electro Metallurgical Division of Union Carbide 
and Carbon Corporation plant at Marietta, Ohio, is a 
large installation for which the insulated or sandwich 
panel was selected after careful engineering studies. De- 
tails of the panel and its connections are shown in Fig. 9. 
The 5-in. thick panel containing a 114-in. layer of insula- 
tion has thermal properties equivalent to much thicker 
walls of solid materials. Simple malleable iron clamps 
bolted to inserts in the concrete fasten the panels to the 
structural girts (Fig. 10). The tongue-and-groove panel 
edge was selected to obtain a watertight joint and to 


Fig. 9. Every third panel of this industrial building is supported on 
a continuous shelf angle thereby transmitting wall loads into the 
structural frame. Clamps fitting over the girts are bolted quickly 
and easily to the panels. Between 2500 and 3500 sq.ft. of walls 
were installed per day. Panel cost was slightly under $2.50 per 
sq.ft. in place. 


WwW 


Fig. 10. The malleable iron clamp used to secure precast concrete 
wall panels to steel frames is a simple, speedy connection device. 
Vertical joints are calked on the interior with a gray material to 
match the concrete and on the outside with a black compound 
for contrast. Inside surfaces of panels were cast on a sheet of 
muslin which dulled and roughened the concrete surface. 


make wall panels self-aligning. Panel sizes are 8x8 ft. and 
8x10 ft. 

Precast concrete wall panels, both solid and insulated, 
were used on the buildings of a pulp mill for Columbia 
Cellulose Company, Ltd., at Watson Island, British 
Columbia. The insulated panels (Fig. 11) were designed 
to prevent condensation on interior surfaces even though 
inside temperatures reached 90 deg. F. with a relative 
humidity of 80 per cent. This requirement necessitated 
continuous insulation through the joints, which was ac- 
complished by extending the insulation to the edges of 
the panels. 

Laboratory tests proved the panels adequate in com- 
pressive, shear and flexural strengths. On this project 
average wall units measure 6x10 ft. and thicknesses are 
5Y4 and 7 in. for the insulated panels and 4 in. for the 
solid panels. The type of connection is similar to that 
described above except that the panels are clamped to 
vertical members of the frame. The dead load of the 


20 0z. Copper flashing oars roofing 


— : co Rigid insulation 


Precast concrete 
roof panels 
Concrete fill 
Wood plate cast 
with panel 


8'x2'"L Horiz. 
girts connected 
to columns 


Vertical girts 
rest on channels 
and I-beams 


Removable 
panel 

I-Beam connect- 
> ed to columns 


Gussets 24"o.c. 
3" Plate 


Insulated precast 
concrete wall panels 


Piece 2210/10 wire mesh 
at each anchor 
Vertical girts 4 3"x3" Ls 


5" Galvanized bolt 
and lock washer 
Malleable iron clamp 
3"Lead sheet under clamp 
Malleable iron anchor 
6x6-8/8 
Wire mesh 


5" Concrete 


2' Cellular glass 
insulation 


2" Concrete 
4" Foam rubber strip 


Asphaltic vapor seal 
Calking compound 


DETAIL 


Fig. 11. Almost 1600 insulated precast concrete wall panels of 
this design were used in building a pulp mill in British Columbia. 
Because of the remoteness of the project, panels were mass- 
produced at the site on the ground floor of one of the buildings. 
Vacuum removal of excess water and 4 hours of steam curing 
helped develop a strong, durable concrete wall panel. A minimum 
of 7 days elapsed before erection. A job-made mobile hoist which 
traveled along the edge of the roof lifted the panels into place. 


wall itself is transmitted through the panels to the founda- 
tion. Over windows and removable panels, 3-in. plates 
welded to the framework serve as lintels. 

The walls of McGaw Memorial Hall, Northwestern 
University, Evanston, Ill., (inside front cover) consist of 
solid concrete panels 8 in. thick and 8 ft. 4 in. square. 
They are clamped to the steel frame using suitable com- 
binations of clip and shim plates. The clip plate is bolted 
to the concrete panel and fits over the girt flanges. Shims 


9 


Fig. 12. A typical panel installation is this project for Dow Chemical 
Co. at Midland, Mich. Besides speed of erection, an additional 
advantage of precast concrete wall panels which appeals to con- 
tractors is the clean, uncluttered type of construction. 


are placed under the clip plates as needed. Horizontal 
and vertical shiplap joints were made watertight with 
sponge rubber and calking material. 

Insulated panels similar to those used on the Electro 
Metallurgical plant were installed on a boiler house for 
Dow Chemical Company, Midland, Mich. (Fig. 12). 
They were transported more than 400 miles from the 
casting plant. 

Arc-welded connections are often used to attach pre- 
cast panels easily and quickly to concrete or steel frames. 
Steel plates or angles anchored in the precast units match 
similar inserts in the concrete frame or abut steel flanges, 
and a fillet weld connects the two. The plates or angles 
are less expensive than special inserts and clamps. If the 
pieces do not match perfectly, fillers or shims can be 
added to bridge the gap. Stud-welded connectors have 
been used satisfactorily on precast concrete projects and 
give a speedy method of attachment. Laboratory investi- 
gations have shown that the heat of welding does not have 
any significant effect on the strength of either the concrete 
or the connections. 


Panel Fabrication 


pi Nsge eaee advantage of precast concrete construc- 
tion is the relative ease with which the various units 
can be produced. Working at floor or table height sim- 
plifies and speeds casting operations. Formwork is at an 
absolute minimum, reinforcement is easily placed in open 
forms, concrete can be worked into all the corners with- 
out difficulty, and surfaces are finished and treated effi- 
ciently. Thus, a durable, high-quality, uniform unit can 
be produced economically. 

Precast concrete wall panels may be cast in either a 
concrete products plant, a temporary casting yard on the 
project, or on the floors of the building in which the 
panels will be used (Fig. 13). The choice of casting site 
depends on the type, size and location of the project and 
on the panel design. Usually the architect or engineer 
considers the probable casting site before deciding on a 
panel design. 

Forms for the panels are designed to comply with 
required tolerances. Casting surfaces may consist of 
leveled, tamped earth or sand; platforms surfaced with 
plywood, plastic-coated plywood or steel sheets; a con- 
crete slab; or special molds of steel, plastic or concrete. 
Edge forms may be of wood, steel or concrete (Fig. 14). 
Initial cost, repairs and number of re-uses are considered 
in determining the minimum form cost per panel. Erec- 
tion and connection methods determine design tolerances 


10 


which are reflected in the selection of edge forms, method 
of bracing, and placing of inserts and reinforcement. 

Precast concrete wall panels are often fabricated by 
mass production methods. The use of pre-assembled re- 
inforcement typifies the technique. A crew cuts and 
bends the reinforcing steel, assembles it into cages and 
attaches inserts. Then reinforcement and inserts are set 
and anchored in the open forms made ready by another 
crew. 

Concrete for precast panels need not be of higher 
strength than cast-in-place concrete. In both cases the 
principles of quality concrete should be followed in 
designing the mix for a durable, weather-resistant wall. 
Early concrete strength affects casting and erection 
cycles. For example, panels which attain strength rapidly 
can be handled sooner and forms are freed for earlier 
re-use. Also, the size of the casting yard is kept to a 
minimum. Similarly, panels can be installed after a 
shorter curing period which reduces the size of the 
storage yard. High-early-strength concrete is used on 
many precast concrete projects, and curing methods to 
accelerate hardening of the concrete are employed in 
both factory-and site-casting. It is not uncommon to cast 
panels on a 24-hour cycle. 

In setting up a casting yard, the contractor must con- 
sider the relationship between yard capacity and the 


PN 


Fig. 13. Panels are often precast on the floor of the building 
(above). In this case a plywood-lined platform was used as a 
casting bed. Mass-production methods are applied to panels 
precast in a plant (above right). Steel forms permit many re-uses. 
Rolling platform, pre-assembled reinforcement with inserts at- 
tached, ready-mix concrete, vibrating table and steam curing 
chambers expedite the production of quality concrete wall panels. 
For large projects similar efficiency can be obtained in a casting 
yard at the site (right). Long, waist-high casting tables make it 
easier to place and finish the concrete. Canvas shelters protect 
panels from cold weather during curing. 


rate of panel installation, or between the output of pro- 
duction equipment and the capacity of handling equip- 
ment. Such consideration will determine the size and to 
some extent the location of the casting yard and will 
affect choice of equipment and materials. Coordination 
of all operations leads to maximum use of equipment 
and greatest efficiency of working forces. 

Once the casting yard is in operation, panel fabrication 
will continue smoothly if all phases are in balance. Be- 
cause of daily repetition, efficiency will improve and final 
cost should decrease. 


Fig. 14. Three types of edge forms are illustrated: Left— Wood 
edge forms in this case were used but once. To conserve space in 
the casting area the panels were built one upon the other. Gener- 
ally, wood forms must be carefully braced if close tolerances are 
specified. Below left—Concrete side forms require little bracing 
and in this case were secured to the base slab by bolting to 
sleepers. The slotted opening in the angle bracket makes it possible 
to slide the forms outward when removing the panels. Below— 
Channel sections are hinged to the casting slab to simplify removal 
of the thin-wall panels from the molds. Dense, smooth concrete 
molds and steel side forms give a large number of re-uses with a 
minimum of maintenance. 


Storage, Handling and Erection 


RECAST concrete wall panels require curing before 

they are erected. During the curing period they are 
carefully stacked in a storage area (Fig. 15). Special 
methods such as steam curing, removal of excess water 
by vacuum from the wet concrete, or application of cur- 
ing compounds are often used before the units are 
brought to storage. Panels made with concrete designed 
to give high early strength can be moved from forms to 
storage as early as 20 hours after casting. Vacuum lifters 
(Fig. 16) can be used to handle precast units at an early 
age as they distribute stresses over relatively large areas 
and thus avoid damage caused by stress concentrations. 

Generally, low- or flat-bed trailers are fitted with an 
A-frame to transport panels, often long distances, from 
factory or precasting yard to construction site (Fig. 17). 
Unit wall costs will increase with the distance moved. 
In one instance an additional cost of 20 cents per sq.ft. 
resulted from a 200-mile haul. Short hauls on the site 


Figs. 15-22. Precast wall panel storage, handling and 
erection methods are pictured. The relatively recent develop- 
ment of the safe, speedy, heavy-duty mobile crane (Fig. 20) 
is considered by many as a basic reason for the increased 
use of precast concrete construction. 


Fig. 15 


may be made by mobile erection cranes, by a straddle 
buggy (Fig. 18) or by a truck-mounted A-frame derrick 
(Fig. 19). 

Panels are usually erected from outside the building 
using heavy-duty, truck-mounted cranes (Fig. 20). On 
large projects, more than 3000 sq.ft. of wall panels have 
been installed per day by a nine-man crew. Panels are 
lifted by attaching lines from the equipment to canvas 
slings or loops of reinforcing bars or bolts anchored in 
the top edges. Anchor inserts in the face of the panels 
are undesirable because they mar the surface. 

Precast panels have been erected from inside the build- 
ing using a fork-lift truck (Fig. 21). This method is ad- 
vantageous if, outside the building, soft ground or limited 
working space makes it difficult or impossible to use 
mobile cranes. On small jobs heavy equipment may be 
too expensive to move in and panels may then be placed 
with hand winches and dollies (Fig. 22). 


Sandwich Panels 


HE combination of materials in the insulated or 

sandwich panel presents special problems. The 
““meat”’ of the sandwich panel is the layer of rigid insula- 
tion between the two layers of concrete. In designing this 
type of panel with various combinations of materials it is 
important to know what heat losses can be expected and 
under what conditions condensation will occur. A knowl- 
edge of the structural behavior of the sandwich panel is 
also essential. 

A typical sandwich panel is analyzed to determine its 
heat transmission coefficient, U, which is a measure of 
the number of Btu’s passing through 1 sq.ft. of the wall 
each hour with a I-deg. F. temperature differential on 
the two sides of the wall (Btu/hr./sq.ft./deg. F.). It is 
calculated from the conductivity, k (Btu/hr./sq.ft./in./ 
deg. F.), of each of the materials comprising the panel. 
The conductivities of the various types of rigid insulation 
are given in the manufacturers’ literature, and of various 
types of concrete in Table I. 

Assume a 5¥4-in. sandwich panel with an interior layer 
of 114 in. of cinder concrete, a 2-in. layer of insulation 
having a k-value of 0.35, and a 2-in. exterior layer of sand 
and gravel concrete. The reciprocals of the conductivities, 
or resistances, are tabulated as follows: 


Component Resistance 


Outside air surface (based on an average 
conductance of 6.0 fora 15 mph wind)* 0.17 


2 in. of concrete (k = 12.6) 0.16 
2 in. of insulation (kK =0.35) ae? 
1¥4 in. of cinder concrete (k =4.9) 0.31 

Inside air surface (based on an 
average conductance of 1.65)* 0.61 
Total Resistance, R 6.97 


Then U=1/R=1/6.97 =0.14. 


Assume, further, that the inside temperature is main- 
tained at 70 deg. F. and the outside temperature is 
—10 deg. F. The temperature change through each 


*See How to Calculate Heat Transmission Coefficients and Vapor 
Condensation Temperatures of Concrete Masonry Walls, available 
free in the United States and Canada upon request to Portland 
Cement Association. 


14 


TABLE | 


(From 1953 Guide, The American Society of Heating and 
Ventilating Engineers) 


Conductivity, k Density 
Type of concrete (Btu /hr./sq.ft./in./deg.F.) (Ib. /cu.ft.) 
Sand and gravel 12.6 142 
Limestone 10.8 132 
Cinder 4.9 97 
Pumice 2.4 65 
Expanded clay 2e3 60 
Expanded slag 1.6 76 
Perlite 0.75 to 1.5 24 to 48 
Vermiculite 0.68 to 1.6 20 to 50 


* 


component of the panel is given by the formula: 
R 
Temp. change (deg. F.) ay total temp. difference 


where R, is the resistance from air to the point in the 
panel and Ris the total air-to-air resistance. Temperature 
of the inside surface is 


0.61 
10° = 597 X80" F. =70° F. —7° F. =63° F. 


A psychrometric chart* shows that condensation will not 
form on the wall surface until the inside relative humidity 
exceeds 78 per cent for the assumed conditions. 

Integral action between the two layers of concrete in 
a sandwich panel is generally obtained by the use of 
shear ties. Strips of expanded metal bent in the shape of 
a channel are often used. They are placed in the bottom 
layer of concrete when it is still plastic and the rigid 
insulation is laid between the strips (see Fig. 3). Pieces 
of welded wire mesh and individual hooked dowels also 
have been used as ties. Characteristics of new insulating 
materials, such as some plastics, give promise of adequate 
bond with the concrete and enough shearing resistance to 
dispense with ties. 

Strength analyses of sandwich panels for wind and 
handling loads are difficult because of uncertainties in 
the interaction of the different materials. For a panel 
differing greatly from those already in use, a field test to 
failure will quickly indicate its strength properties. 


Textures 


| Beas texture of the panels on the 550 Building (Fig. 5) 
was obtained by coating the face of the form with a 
material which retarded the setting of cement paste 
coming in contact with it. A thin layer of facing concrete, 
consisting of white portland cement and white quartz 
aggregate, was placed in the forms and backed up with 
lightweight concrete. When the panel was removed from 
the form the exterior surface was wire brushed to expose 
the quartz aggregate. Care was taken in placing back-up 
concrete to prevent it from displacing the facing concrete. 

A similar treatment was given precast wall panels on a 
school in California. They were cast in a factory, again 
with a quartz aggregate exterior surface. In this instance, 
low-slump concrete was placed and vibrated first, fol- 
lowed shortly after by the 34-in. facing concrete. Twenty- 
four hours later the top surface was wire brushed to bring 
the red quartz aggregate into relief. 

Precast panels without special surface aggregates can 
be textured with a broom or a swirl finish. Either finish 
tends to reduce formation of surface hair cracks, adds 
to the architectural appearance of the wall, is inexpensive 
and can be obtained in the field as easily as in a plant. 
A straw or fiber broom drawn over the trowelled surface 
gives a roughened texture such as is seen in closeup on 
the cover and in Fig. 23. Rubbing a nearly hardened panel 
surface with canvas or heavy paper gives the swirl finish 
shown in Fig. 23. 

Other textures are obtained by casting precast panels 
on various form liners. For example, the sandwich panels 
shown in Figs. 9, 10, and 12 were cast on a sheet of muslin 
and the panel in Fig. 3 on canvas. This treatment tends 
to remove the slick finish resulting from casting on a 
smooth surface. The sill panels on the feed mill (inside 
cover) were cast on corrugated metal. With imagination, 
an unlimited variety of effects is possible because con- 
crete can be easily molded when it is cast. 


The drawings in this publication are typical designs and 
should not be used as working drawings. They are intended 
to be helpful in the preparation of complete plans which 


should be adapted to local conditions and should conform 
with legal requirements. Working drawings should be pre- 
pared and approved by a qualified engineer or architect. 


Fig. 23. Precast concrete wall panels with a broomed finish (above) 
give a uniform appearance to the walls of an industrial building. 
From a distance the individual grooves are not apparent but the 
rough texture enhances overall wall appearance. A swirl finish 
(below) on the precast panels of a school in Colorado is a pleasing 
architectural effect which needs no further treatment and little 
periodic maintenance. 


Printed in U.S.A. 


THE 212-BED East Tennessee Baptist Hospital, Knoxville, under con- 
struction in 1947. Cost approximately $2,000,000, including all equip- 
ment. This is about $13.50 per sq.ft. of floor space. A 9 per cent saving 
in total cost of construction was made by using concrete in this building. 
Concrete frame and floor construction reduces costs, leaves additional 
funds for much-needed hospital equipment. J. R. Edmunds, Jr., architect; 
Barber and McMurray, associate architects. 


REINFORCED CONCRETE FRAME is used in this new 8-story office 
building of the New York Housing Authority. Concrete construction can 
start as soon as foundation loads are determined—time saved in con- 
struction means earlier occupancy. Fellheimer and Wagner, architects. 


in building schools — apartments — 
hospitals — other structures 


CONCRETE Frames and Floors 
Mean Time and Money SAVED 


The buildings shown in this folder illustrate the use of 
concrete frames and floors—a use that permits greater 
latitude in design, speeds construction and cuts building 
costs. 

Whether used in apartments, hospitals, office buildings 
or schools, concrete construction means greater freedom 
and flexibility in room layout. Partitions can be located 
where they are most desirable. Columns can be placed 
wherever convenient to leave maximum usable space. 
The use of concrete frames and floors enables designers 
to reduce the total building height without decreasing the 
ceiling height of individual floors. 

The economy of concrete reduces cost of frame con- 
struction, based on the columns, floors and ceiling treat- 


~ + feanm O95 ra’ d 4 
ment, 1rOm 25 to 49 per cent pet sq.ft. as compare with 


other types of construction. Regardless of structural re- 
quirements, there is a type of concrete frame and floor 
construction for each job. In low buildings as well as 
multistory structures, the use of concrete frame construc- 
tion means lower costs. 


OMISSION OF INTERIOR BEAMS in the flat 
plate floor construction of the New York City 
Housing Authority's new office building per- 
mits free use of movable partitions to meet 
occupant’s needs. Concrete construction en- 
abled designers to meet both minimum story 
height andconstantceiling heightrequirements. 


PRINTED 


IN U.S.A. 


FLAT PLATE REINFORCED CON- 
CRETE FLOORS designed as continu- 
ous frames as illustrated by the 
Clinton Hill Housing Development, 
Brooklyn, resulted in a large saving 
in frame and floor cost. Columns are 
prismatic from floor to floor, slabs 
are of uniform thickness, and beams 
are used only in walls and the serv- 
ice area that includes stairs and ele- 
vators. Harrison, Fouilhoux and 
Abramovitz, architects; J. DiStasio, 
engineer. 


Builc 
CO} 


SLAB AND COLUMNS in the Clinton Hil 
Housing Development, Brooklyn, are o: 
reinforced concrete construction with ne 
special devices required to increase the 
strength of the slab in the column head 
region. Flush ceilings facilitate the par. 
tition arrangement and save headroom 


4 


4 
; 
COPYRIGHT, 1948 B 


REINFORCED CONCRETE FRAMES AND FLOORS are z 
used throughout the 10 James Weldon Johnson houses THE NEW YORK HOUSING AUTHORITY has proved that more housing 


in Manhattan. This $6,500,000 New York Housing Au- for less money is possible when concrete frames and floors are used. 
thority project, which will house 1,310 families, floes This interior view shows one of the James Weldon Johnson apartments, 
trates the economy of concrete frames and floors in Manhattan, another project that demonstrates the adaptability of con- 
iaydeevetias high buildings crete to the requirements of apartment buildings. H. M. Prince, J. 

Whittlesey and R. J. Reilly, Associated, architects; Charles Mayer, 
structural engineer. 


Bow at LOWER COST with 


RETE Frames and Floors 
nomical for beth low buildings and multistory sucliures 


CONCRETE FRAMES AND FLOORS were 
selected for the vast new $30,000,000 
New York Life Insurance Housing Project, 
near Flushing, L. |., after a careful study of 
costs, speed of construction and other im- 
portant factors. Painted undersides of 
floor slabs make inexpensive but attrac- 
tive ceilings. More than 3,000 families will 
live in the 138 two- and three-story byild- 
ings and 2 thirteen-story buildings¥Bor- 
hees, Walker, Foley and Smith, architects; 
Fred N. Severud, structural engineer. 


S-149—40M—1-48 


=MENT ASSOCIATION 


_-_ eer Worrorwt aivoy ~~ 
°° ° QUIPE ONDY 


7 SOO] ‘SOWDI 


Sele a ON: @ 


"AB Td ‘79S 29S 


we sea 


CONCRETE FRAME CONSTRUCTION can be adapted to meet any requirement. Here a wide shallow 
beam in the center portion of one of the units of the John Lovejoy Elliott apartments, New York City, 
permits flexibility in locating interior columns. The underside of the floor slab, when left exposed 
and painted, makes an attractive ceiling at minimum cost. Another view of the Elliott project is shown 


on the front of this folder. William Lescaze and Archibald Manning Brown, architects; Fred N. Severud, 
structural engineer. 


Write to nearest district office for booklets, 
Continuity in Concrete Building Frames, a 
practical analysis for vertical load and wind 
pressure, and Handbook of Frame Constants to 
facilitate design calculations. J 


Atlanta 3, Ga...sssseeeeeeeeeees «Hurt Building 
Austin 16, Tex...1301 Capital National Bank Bid ys 
Birmingham 3, Ala............+-.504 Watts Bldg. 


Chicago 10, Ill...........-..-33 W. Grand Ave. 
Columbus 15, Ohio.............50 W. Broad 


Kansas, Gity 6, Mo..< «cis uemieelO27 Dierks Bldg. 
Lansing 8, Mich.........+++++++Olds Tower Bldg. 


Milwaukee 2, Wis............-735 N. Water S I 
Minneapolis 2, Minn...916 Northwestern Bank Bldg. 
New York 17, N. Y......++++++347 Madison Ave. 
Oklahoma City 2, Okla...1308 First National Bldg. 
Omaha 2, Neb... s.s0s00 oes ees O4 osetia 
Philadelphia 2, Pa............+-1528 Walnut St. 
Richmond 19, Va...1210 State Planters Bank Bldg. 
Seattle 1, Wash............903 Seaboard Bldg. 
Spokane 8, Wash........Old National Bank Bldg. 
St. Louis 1, Mo.........+-907 Syndicate Trust Bldg. 
Vancouver, B. C., Can.........+.318 Shelly Bldg. 

Washington 4, D. C......837 National Press Bldg 


PORTLAND CEMEN 
ASSOCIATION 


The activities of the Portland Cement Association, a national organizatio 
service, promotion and educational effort (including safety work), and are primari 
of the Association and its varied services to cement users are made poss 


the manufacture and sale of a very large proportion of all portland « 


n, are limited to scientific research, the development of new or improved products and methods, technical 


arily designed to improve and extend the uses of portland cement and concrete. The manifold program 


CURVILINEAR FORMS 
in architecture 


published by PORTLAND CEMENT ASSOCIATION 


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CURVILINEAR FORMS 
in architecture 


This issue of the newly christened Concrete In Archi- 
tecture is devoted to that fascinating new roof type—the 
concrete shell. Never before has there been available to 
architects a roof with the protean capabilities of shells. 
The margin of compromise between the idealized space 
enclosure for any given building and its practicable real- 
ization has been narrowed to a point never before 
achieved. Shells in their countless variations can be 
curved and angled to suit individual needs.in a manner 
unique in this field. 

In addition, the practicalities of shells are as impres- 
sive as their architectural prowess. Their curved shape 
imparts a strength that amazes many. The sight of a 
3-in. shell spanning 180 ft. is enough to evoke awe from 
experts and laymen alike. Materials, then, are reduced 
considerably. New developments in formwork—notably 
the traveling form—have greatly lowered this cost item. 
Acoustical considerations are simplified, thanks to the 
shape of shells. 

Despite this formidable array of practical attributes, 
perhaps the most appealing characteristic of shells is 
their glamor. For people within or outside the industry 
who see expressiveness and romance in buildings, as 
well as utility, shells set new, broader horizons. 


ea oS | 
ASS 
= me 


PORTLAND CEMENT ASSOCIATION, 33 WEST GRAND AVENUE, CHICAGO 10, ILLINOIS 


The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products 
and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of port- 
land cement and concrete. The manifold program of the Association and-its varied services to cement users are made possible by the financial support of 
over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in 
these two countries. A current list of member companies will be furnished on request. 


©PORTLAND CEMENT ASSOCIATION, 1960 Printed in U.S.A. 


CURVILINEAR FORMS 
in architecture 


This issue of the newly christened Concrete In Archi- 
tecture is devoted to that fascinating new roof type—the 
concrete shell. Never before has there been available to 
architects a roof with the protean capabilities of shells. 
The margin of compromise between the idealized space 
enclosure for any given building and its practicable real- 
ization has been narrowed to a point never before 
achieved. Shells in their countless variations can be 
curved and angled to suit individual needs.in a manner 
unique in this field. 

In addition, the practicalities of shells are as impres- 
sive as their architectural prowess. Their curved shape 
imparts a strength that amazes many. The sight of a 
3-in. shell spanning 180 ft. is enough to evoke awe from 
experts and laymen alike. Materials, then, are reduced 
considerably. New developments in formwork—notably 
the traveling form—have greatly lowered this cost item. 
Acoustical considerations are simplified, thanks to the 
shape of shells. 

Despite this formidable array of practical attributes, 
perhaps the most appealing characteristic of shells is 
their glamor. For people within or outside the industry 
who see expressiveness and romance in buildings, as 
well as utility, shells set new, broader horizons. 


CURVILINEAR FORMS IN ARCHITECTURE 


The Pantheon and the Olympic Sports Palace 


By Clovis B. Heimsath 


“The Pantheon remains a Pantheon even if it were 
built in light reinforced concrete. ... The use of curvi- 
linear forms today should be to implement the modern 
approach; it should be an instrument of freedom. To 
this end techniques and visual-isms are not enough. 
A total architectural vision is needed.” 


Bruno Zevi 
Editor, L’architettura 


Single and double curvature forms in reinforced con- 
crete are having a profound effect on contemporary de- 
sign. The geometry of the T-square is being supple- 
mented by the geometry of the curve. These dynamic 
structures are heralding a new era in curvilinear archi- 
tecture. A structural form, however, is not im itself a 
piece of architecture; it must become a part of a total 
composition and be related to the overall design. The 
statical properties of these new forms in concrete must 
be studied along with the architectural implications of 
their use. Only then can a “‘total architectural vision’’ 
of which Bruno Zevi speaks become apparent. 

Curved forms, however, produce some unique prob- 
lems in design which must be discussed at the onset. For 
example, a rectilinear volume can be completely de- 
scribed in plan, section and elevation, while a compara- 
ble curved volume requires an infinite number of plans 
and sections for the same description. In complicated 


THE AUTHOR: Clovis Heimsath, a graduate of Yale 
University and the University of Texas, was awarded 
the Frank M. Patterson Scholarship, the A.I.A. award 
from the Henry Adams Fund, and a Fulbright Scholar- 
ship for study in Italy. He was formerly associated with 
Pederson and Tilney, New York and New Haven, and 
Harrison and Abramovitz, New York, and is currently 
a project architect in the Design Development Group 
of Voorhees, Walker, Smith, Smith and Haines, New 
York. He is the.author of several penetrating articles in 
leading architectural journals. 


curved forms this problem is particularly acute, as in 
the New York TWA Terminal Building by Eero Saarinen. 
Since he found it extremely difficult to indicate the struc- 
ture’s contours by conventional means, he was forced 
to use consecutive photographs of a large-scale model 
to determine the profiles. Perhaps new methods will be 
developed to overcome this difficulty with smaller ex- 
penditures of time and money. However, until then, the 
technique of graphic presentation must be mastered by 
the architect. 

A more fundamental problem in curvilinear architec- 
ture is that of scale. A paraboloid can be 10 ft. high ‘or 
100; by itself it does not indicate its size to the viewer. 
Conventional scale elements such as doors, windows, 
stairs, etc., are often difficult to combine with the new 
forms—new scale elements are needed particularly suited 
to curved forms. 

Again, there is the problem of visualizing curvilinear 
spaces. A dome may have the same volume as a recti- | 
linear polyhedron, yet the impression on the viewer is 
very different. In a dome, the space rises toward the 
center in a constant manner from all points of the sur- — 
rounding circumference. The space encompasses the 
viewer. The rectilinear volume, on the other hand, is 
experienced as a series of planes, each independent of 
the other. The feeling of spatial continuity within a 
dome is a unique characteristic and as such has a unique 
architectural character. Similarly, other curvilinear 
volumes create unique impressions; the study of these 
“spatial personalities’ is important if they are to be 
used with maximum effectiveness. 

Such design problems point to the need for greater 
familiarity with these three-dimensional shapes. This 
need; in turn, leads naturally to research of various 
kinds. Where can one turn to gain greater familiarity 
with the vocabulary of curved forms? One direction is the 
study of geometry. The geometrical properties of curva- 
ture can shed light on the problems of combining forms 
and prove a source of abstract inspiration.* A second 
study, of equal importance, is the tradition of Western 
architecture. A great deal can be learned from the works 
of the past that have real application today. In this 


*Stephan Cohn-Vossen and David Hilbert, Geometry and the Imagination, Chelsea 
Publishing Co., New York, 1952. 


Transition between the 
great rotundaofthe Roman 
Pantheon andits rectangu-~ 
lar portico was a problem 
for the architect of 120 A.D. 
The solution was less con- 
vincing because the cor- 
nice line of the connecting 
structure does not line up 
with the cornice of the ro- 
tunda. 


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regard, a comparison of the Pantheon, 120 A.D., with 
the Olympic Sports Palace, 1958 A.D., is pertinent. 
The Pantheon was built by the Roman Emperor 
Hadrian for the worship of pagan gods. It is a great 
circular rotunda 142 ft. in diameter and with an equal 
dimension in height. The structure consists of a concrete 
wall 20 ft. thick supporting a hemispherical dome of 
brick and light mortar. An unglazed opening 27 ft. in 
diameter at the crown of the dome provides the only 
source of light within the volume. The inner surface of 


the dome is coffered, the mouldings of which are visually 
foreshortened in relation to the viewer standing below. 
These coffers provide a powerful design feature, as can 
be seen in the closeup photograph. It is thought that 
these were originally filled with star motifs to heighten 
the symbolism of the dome form as a “‘dome of heaven.” 
The cutaway section shows the complexity of the bear- 
ing walls. A system of relieving arches carry the load 
across the recessed niches; these arches of brick were 
infilled with rough concrete. 


Entrance to the rotunda is through an imposing rec- 
tangular portico, which had originally been part of the 
Temple of Agrippa. In adding the rectangular portico 
to the circular dome the ancient architect faced the 
problem we often face today in relating two geometries. 
His approach was to add a connector between the two 
forms, thus creating a third element in the composition. 
This connector, unfortunately, is not well related to 
either geometry, and the transition between the drum 
and portico thus is not convincing. (The cornice line of 
the front structure does not line up with the cornice of 
the rotunda.) 

It is interesting to note that this problem of con- 
nectors, which comes up every time a circular audi- 
torium must be combined with a rectangular office wing, 
is a problem at least 1,800 years old! The Pantheon is, 
however, an impressive structure. The exterior mass is 
ponderous, a visual wall of masonry. The great diameter 
of the rotunda creates a form that “flattens out;” the 
impression of a circular form is almost lost on the exte- 
rior since the degree of curvature at any point is slight. 
This is a visual characteristic of large-diameter forms, 
which is as true today as it was then. Entering the 
Pantheon is an experience. One feels insignificant be- 


A powerful design feature of the Pantheon’s interior are 
these coffers on the hemispherical dome, with visually 
foreshortened mouldings. 


tween the great columns of the portico; moving into the 
rotunda one is struck down. The puny spectator is over- 
powered by the awesome space. It seems indeed to be 
the home of pagan gods; there is little sympathy for the 
human in the severe encompassing space. In 608 A.D. 
the Pantheon was dedicated as a Christian church, but 
to little avail, for the space will not change and the space 
is pagan. 

The Pantheon expresses its program well—the scale 
of the elements below the dome is monumental, the 
coffered hemisphere spans awesomely above, the “‘eye”’ 
at the center is a focal point 142 ft. above the spectator. 
It stands as a great brooding mass, a monument that 
speaks eloquently of the Roman mind. It is a brilliant 
feat of construction. But more important, the structure 
and the program merge to create a unique architectural 
personality. 

A few miles away is the recently completed Olympic 
Sports Palace by engineer Pier Luigi Nervi and Italian 
architect Annibale Vitellozzi. This light concrete struc- 
ture took 40 days to build (the Pantheon took four years). 
It spans 194 ft. and the thrust of the dome is transmitted 
to the ground via 36 Y-shaped piers. The impression 
given by this form is in complete contrast with the 


The complexity of the bearing walls and the arches that 
carry loads across the recessed niches are shown in this 
cutaway of the Pantheon. 


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Pantheon. The scale is human and the space is pleasant. 
As the Pantheon expresses the awesomeness of gods, 
the Sports Palace suggests the cordiality of a social 
gathering. This friendliness is the result of the handling 
of particular architectural elements. 

Whereas the dome of the Pantheon is a hemisphere 
rising high above the spectator, the Sports Palace is a 
segment of a sphere with a gentle slope. The whole 
undersurface of the dome is articulated by intersecting 
ribs, expressing the prefabricated method of construc- 
tion and creating a pleasing geometric pattern. A person 
feels related—by the scale of the pattern the dome be- 
comes a friendly thing. Again, the dome is lit from the 
circumference and visually seems to ‘‘float’’ overhead. 
Most important, the viewer feels the depth of construc- 
tion. From outside the Pantheon it is difficult to predict 
what the inside will be; from the inside it is hard to 
know what the form is without. Essentially, there are 
two Pantheons—one exterior and one interior. In the 
Sports Palace, on the other hand, every effort has been 
made to express one building. By seeing the depth of 
construction one knows the dome is thin and can predict 
what the form will be on the other side. From within 
it is possible to see through the structure to the exterior. 


Visually, this “reading” of the building in depth is re- 
assuring. There are no mysteries here; the viewer can 
relax and enjoy the space. 

These two buildings, separated by centuries, can 
teach much about the vocabulary of curvilinear form. 
A dome can become an ominous thing or a friend; it 
can float as a canopy overhead or weigh heavily on 
its supports. One is not “‘right”’ and the other “‘wrong.”’ 
Rather they are different expressions of the same vocab- 
ulary. In the past, curved forms played an important 
part in the design composition. The variety of forms 
that were evolved is impressive; a “‘trulli’’ house, a me- 
dieval town hall, a cloister, a rural church—these are 
only a small part of a vocabulary that includes the whole 
of the Byzantine and Baroque periods. 

The architect is no longer tied to the limitations of 
masonry construction. With reinforced concrete he can 
create a variety of new forms. He can project far beyond 
the symmetrical geometries of the past; yet the psy- 
chological impressions of his forms must be considered 
as much today as in earlier periods. The vocabulary of 
curved forms as used in the past must be grasped again 
today. Only then can a true architectural expression of 
reinforced concrete be fully realized. 


Lit by a 27-ft. opening at the crown of the dome, the Pantheon’s awesome interior overpowers the spectator. 


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Despite its brooding mass, the Pantheon was a brilliant 
feat of construction that speaks eloquently of the Roman 
mind. 


A pleasing geometric pattern of intersecting ribs and 
circumferential lighting contributes to the friendliness 
of the Sports Palace. 


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CHARACTERISTICS OF SHELLS 


Man has long associated strength with mass. 
That undoubtedly explains his difficulty in re- 
lating strength to space geometry. The propor- 
tions of post and lintel seem to tell him of their 
own structural adequacy, and even minor depar- 
tures from the norm transmit to an experienced 
eye the impression of a daring design or the 
sense of great strength. This norm is so inbred 
that when a departure is made to shell construc- 
tion, the comparative thinness of the membrane 
induces the wonder of Alice through the looking 
glass. 

Strangely enough, since the dawn of history 
man has sporadically utilized a spatial arrange- 
ment of supporting members to obtain necessary 
strength with minimum material. It is feasible 
to conjecture that the first example of this may 
have occurred during prehistoric times when a 
wandering tribe, attempting to ford a deep, fast- 
flowing stream, took advantage of vines that hung 
from one bank to the other. Conjecture is not 
necessary in the case of China where there are 
records of suspension bridges that date back 
thousands of years. Thousands of miles to the 
west, in Mesopotamia, thin arches which pre- 
date the Christian Era are still standing. 


SPACE GEOMETRY 


Why does spatial arrangement lead to more efficient 
use of materials? This question can be answered best 
by first considering the comparatively simple case of a 
two-dimensional structure. 

Loads are resisted in a beam by compressive forces 
at the top fibers and tensile forces at the bottom, as 
indicated by arrows in Fig. la. The stresses will vary 
from zero at the middle of the beam to maximum values 
at the outermost fibers. For this reason, most beams 
are made with flanges in order to reduce the amount of 
material not working at top efficiency. Furthermore, 
stresses in the beam, if it is of constant depth, vary 
throughout its length and are at maximum magnitude 
only at midspan. Therefore, only one specific point in 
the beam is worked to its greatest efficiency. 


The resistance of a beam to loads is primarily a func- 
tion of its depth—the shallower the beam, the higher 
will be the forces that are developed. On the other hand, 
when a concentrated load is carried by a cable, the load 
is resisted solely by tension in the cable (Fig. 1b). The 
entire cable is subject to the same stress irrespective of 
its profile. Thus every square inch of a cable of proper 
size is worked to its maximum efficiency. It is im- 
portant to note that in such a case stress is a linear 
function of the amount of cable sag. In other words, for 
a given load and area of cable, the stress varies in direct 
proportion to the sag. An obvious corollary is that the 
area of cable required to resist a given load is related 
almost directly to the sag. 

An analogy can be drawn between the behavior of 
cables and beams. It can be deduced that for a beam 
having a depth equal to the sag of a cable, the areas 
required for each beam flange and the cable are iden- 
tical. Since equal top and bottom flanges are required 
in beams of the same material as the cable, at least 
twice as much cross-sectional area is needed by the 
beam to handle the same load. In the case of the beam, 
the load is resisted by what is termed flexural or bend- 
ing action. In the cable the load is resisted by what is 
generally termed membrane or direct action. 

To summarize this simple two-dimensional case, the 
resistance of the cable is developed mainly by direct 
forces (pure tension) while the beam resists by what is 
called flexural action. 

There is, however, a significant difference in the be- 
havior of the two systems. If two or more loads are 
placed on a beam, its shape does not change. Instead 
the curve assumed by the cable varies as the distribu- 
tion of the load. Thus, when two loads are applied, the 
configuration changes to that shown in Fig. lc. Only 
if the load is continuous over the cable would a smooth 
catenary curve be obtained (Fig. 1d). From a functional 
point of view, these variations in cable configuration 
are a decided disadvantage. 

Since the arch is, in essence, an inverted cable, stresses 
within it are mainly compressive (Fig. 2). However, an 
arch is designed to have sufficient stiffness to render it 
insensitive to load variation. 

This direct action is one of the distinguishing charac- 


Fig. 2 


om 


a. Flat slab b. Curved slab 


teristics of shell behavior. For example, if a simple plate 
is cantilevered from a support, as shown in Fig. 3a, its 
resistance to a load is a function of the width and thick- 
ness of the plate. As shown, the plate resists its load by 
purely flexural forces, as in a beam. On the other hand, 
if the same plate is curved in cross-section (Fig. 3b) the 
resistance to load is mainly a function of the chord 
width and the rise or distance between the valley and 
the crown. 

This change in geometrical form profoundly alters 
the resistance of the plate. Whereas stresses in flat plates 
vary linearly from the top to the bottom surface, the 
stress at any elevation in a shell is practically constant 
throughout its thickness. Accordingly, there is little or 
no bending moment in the curved plate. Although the 
internal forces vary from top to bottom, they are in the 
nature of direct tension and compression. In this case, 
the upper fibers are in tension and the lower in com- 
pression. i 

The increase in load-carrying capacity in this type of 
shell is due primarily to the fact that the lever arm of 
the resisting forces has been increased significantly. In- 
stead of being equal to merely the slab depth, it now 
amounts to the rise of the shell. Thus, through space 
geometry alone, it is possible to increase the strength 
of a plate a hundredfold. 

It is interesting to note that transverse behavior is 
also radically changed. In the case of the flat plate, non- 
uniform loads cause transverse bending, i.e. normal to 
those shown. In shells, however, the load is resisted 
transversely essentially by arch action, even though the 
longitudinal edges or valleys of the shell are totally un- 
supported. This arch action illustrates one important 
difference between the behavior of a shell and a cable. 
In a draped cable, the cable itself adjusts to any load 
change by altering the shape of the curve. In a shell, 
changes of load intensity do not result in changes of 
shape, but cause merely a redistribution of internal re- 
sistance. This is the primary advantage of the shell 
form. 

This brings up a point around which some confusion 
exists. The general concept that a shell is any plate 
curved in space is in some measure misleading. In addi- 
tion to geometrical considerations there are, in most 
cases, certain boundary conditions that must prevail if 
true shell action is to be achieved, i.e. if the curved 
plate is to resist the load principally by direct forces 
acting in the plane of the shell. . , 

Before discussing boundary forces in three-dimen- 
sional structures or shells, reference should be made to 
the boundary conditions encountered in arch action. 


To secure arch action, the axis of the member must 
not only be curved in space, but the footings must also 
be capable of supplying restraint both vertically and 
horizontally. For example, a parabolic arch ideally re- 
strained, with sufficient rise and with uniform loading, 
is subject merely to axial compression (Fig. 4a). If such 
an arch was supported on rollers at one end, it would 
behave simply as a beam (Fig. 4b); in spite of the rise 
or curvature, it would be subject to high bending mo- 
ments without thrust. Therefore, if the necessary re- 
straint is lacking, the entire advantage of spatial ar- 
rangement is lost. 

Horizontal restraint is not needed in a few exceptional 
cases; for example, an arch having the shape of half an 
ellipse and subject to the proper combination of vertical 
and horizontal loading. In general, however, it can be 
stated that horizontal restraint is a necessary condition 
for the creation of arch action. 

To achieve shell action, similar requirements are en- 
tailed in order that the curving form be almost com- 
pletely free of bending. It is difficult to state the bound- 
ary conditions for all cases, but a few illustrations will 
show the requirements that are usually necessary. 


For example, for the barrel shell in Fig. 5 to be com- 
pletely free of bending, restraint at supports is required 
along the two curved boundary edges as well as along 
the longitudinal boundaries. The amount of restraint 
needed, however, is not of equal importance at all the 
edges. Lack of freedom along the longitudinal edges 
would merely lead to a slight bending moment. In most 
cases, this would not be significant. The moments are 
usually quite small; for this reason, shells only 31% in. 
thick can be made to span distances up to 300 ft. longi- 
tudinally. On the other hand, the absence of suitable 
restraint along the circumferential edge of even moder- 
ate spans would cause bending moments large enough 
to exceed the capacity of a 4-in. thick shell. 

The same necessity for edge restraint also applies to 
doubly curved shells that are rectangular in plan. The 
support for the shell shown in Fig. 6 is completely with- 
out lateral resistance. Despite this fact, the shell will 
be free of bending providing the supporting members, 
shown as ribs, are capable of resisting shears that are 
transmitted to the ribs by the shell. 

The importance of tangential shears is more evident 
when one considers the means by which the effect of a 
load is transmitted to the support. Therefore let us ex- 
amine a shell independently of its supporting ribs. For 
the shell to be stable, it is necessary that the sum of the 
vertical forces along its perimeter be equal to the total 
load on the shell. If the edges of the shell are horizontal, 


as in Fig. 7, these forces will be perpendicular to the 
plane of the shell. As such, bending forces are created 
in the area near the boundaries. For small areas—as 
30 ft. by 30 ft.—these bending stresses can be tolerated 
with the normal thicknesses of shells. However, for a 
sizable area—in the range of 50 ft. by 50 ft. and greater 
—a marked increase in shell thickness is required to 
resist the flexural forces. 

If the edges of the shell are curved vertically, as in 
Fig. 8, the vertical forces can be supplied as a compo- 
nent of the tangential shear. With the edge forces tan- 
gential, the internal stresses at the boundary must be 
axial since shear of this type induces merely compres- 
sion or tension. 

In brief, the ability of a curvilinear layout to act as 
a shell can be best surmised by examining the area near 
the supports. The reaction to loads must enter the shell 
in its plane. In most cases, this is accomplished for the 
three popular shapes shown in Fig. 8 by means of ribs 
or stiffeners. 

It should be pointed out that it is not necessary for 
all shells to have ribs. For certain cases, shells can be 
built without such rigid supports. The absence of ribs, 
however, almost always requires a thickening of the 
shell near the support or other special considerations. 
For example, barrel shells without edge beams have 
been built with column spacing of 45 ft. by 60 ft. In 
such cases, a portion of the shell is assumed to act as 
an arch spanning between columns. To reduce arch 
stress in the thin section, a considerably higher rise is 
necessary. 

Another layout which does not require ribs, except 
for large spans, is that made by intersecting hyperbolic 
paraboloids (Fig. 9). For this case the intersections 
form a V-trough which acts as a stiff arch to support the 
shell proper. This layout is particularly economical be- 
cause the dead load condition produces pure compres- 
sion throughout the entire structure. 

The conventional dome formed as a surface of revolu- 
tion (Fig. 10) is likewise completely free of bending, if 
the reactions are tangential to the edges, even when 
supported at isolated points. 

One of the decisions a designer must make when using 
shells is the selection of one of the infinite variety of 
shapes possible. Although the opportunity to choose 
from many shapes is highly desirable from an esthetic 
viewpoint, it is important that careful attention be given 
to selecting the type that most adequately serves the 
desired purpose. The following discussion of the proper- 
ties and characteristics of various shells is offered as an 
aid in making such decisions. For this purpose, shells 


will be classed as singly or doubly curved on the basis 
of their behavior. 


SINGLE CURVATURE SHELLS 


Shells of single curvature, as the name implies, are 
formed by translating an arc along a straight axis. This 
arc can be parabolic, elliptical or any other shape, al- 
though the cylindrical curve generally is used for ease 
of construction and analysis. Although not readily ap- 
parent, the folded plate is also in this category as it is 
formed, in essence, by two plates with an interior ob- 
tuse angle translated along a straight axis. 


BARREL SHELLS 


The barrel or cylindrical shell adapts itself well to 
various architectural effects, as shown in Fig. 11. It is 
an economical roof for a wide range of spans and is quite 
suitable for chord widths greater than 30 ft. Greatest 
economy is usually attained when the span is about 
twice the chord. There is considerable leeway in this 
respect, however, and marked deviations from this pro- 
portion often will not materially alter the cost. 

Most shells having chord widths equal to one-half 
their span require a rise of about one-tenth the span, 
However, rise is dependent on two factors—the ratio of 
the chord width to the span and the degree of structural 
continuity in the longitudinal direction. Hence, in some 
cases where the span is long compared to the chord, a _ 
rise of one-twelfth the span can be tolerated without 
leading to excessive use of reinforcement. On the other 
hand, for very long spans with low chord-to-span ratios 
it is sometimes impossible to obtain sufficient rise for 
structural adequacy. In these cases, integral edge beams 
can be provided along the longitudinal perimeters of 
the shell. This type of construction has been used for 
spans as great as 200 ft. 

A shell used extensively for structures such as field 
houses is the short barrel, 1.e. one having a chord width 
considerably greater than the spacing or span between 
ribs (Fig. 12). Rib spacing for short barrels is deter- 
mined, to a large extent, by the number of bays and 
desired reuses of forms. Spacing can vary from as little 
as 22 ft. to as much as 35 ft. Shell thickness used is the 
minimum consistent with good construction practices 
and adequate cover for reinforcement, but a slight thick- 
ening of the shell in the vicinity of the ribs is customary. 


FOLDED PLATES 


Many interesting roof combinations are possible with 
folded plates (Fig. 13). As a matter of fact, rectangular 


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a. Arch action b. Beam action 


Shell action 
Fig. 5 


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plates are not a requisite for this type of construction. 
Triangular plates can be used to obtain three-dimen- 
sional action, as illustrated in Fig. 14. However, a word 
of caution is needed for this latter type. For moderate 
spans up to 50 ft., plate thicknesses in the range of 4 in. 
will be adequate. For longer spans and more intricate 
arrangements of the triangular plates, concentration of 
resistance occurs at the corners, and thickening of the 
slab in some areas is required. 

The V-type folded plate is especially suitable for col- 
umn spacings, transverse to the folds, of less than 25 ft. 
This is due primarily to the fact that the folds act as 
continuous plates in the transverse direction, with the 
result that negative moments are created along the 
ridges. When the distance from one junction to the next 
exceeds 15 ft., bending moments become quite large, 
especially in the exterior bay, and cannot be adequately 
resisted by 4-in. slabs. 

When transverse spacing of columns is greater than 
25 ft., the three-plate arrangement shown in Fig. 13b 
should be used. With this type, transverse column spac- 
ing can be as much as 45 ft. These V-type folded plates 
connected by horizontal slabs give adequate concrete 
area to resist compression at the top. 

Support requirements for this shell type are eco- 
nomical. Cost comparisons for various heights indicate 
that a rise of one-fifteenth of the span will usually result 
in the most economical structure. However, cost per 


a. Multiple 


b. North light 


c. Butterfly 


square foot does not increase inordinately with varia- 
tions in height; departures from the optimum ratio are 
often practical both structurally and economically. 

With regard to reinforcement costs, folded plates re- 
quire more reinforcement than barrel shells of equal 
span and chord width. However, the increased cost of 
additional reinforcement is offset by more easily fabri- 
cated formwork. 

A special merit of the folded plate is that heavy loads 
can be supported at the intersections. In some struc- 
tures, a complete lower floor or balcony has been sus- 
pended from this type of roof. 

Although the basic geometry of barrel shells and 
folded plates represents curvature in one direction, indi- 
vidual elements can be combined to form dome-like 
structures. Many variations are possible; a few of the 
most popular are shown in Fig. 15. 

A design that is widely used for spans up to 100 ft. is 
the tapering folded plate shown in Fig. 15c. When this 
roof is unsupported at the center, the ridges are sloped 
downward to the perimeter to reduce stresses at the 
crown. In addition, a heavy tie or abutment is used 
around the perimeter to absorb the outward thrust cre- 
ated by the inclined folds. When desired, lantern open- 
ings can be located at the crown. 

The segmented barrel dome, shown in Fig. 15a, is 
especially suitable for spans in excess of 100 ft. The 
shell in this particular layout is supported by ribs placed 


d. Corrugated 


e. Combination 


Long barrels 


Fig. 11 


a. Rigid abutments 


b. Arch support c. Segmented d. Rigid frame support 


Short barrels 


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ORES 


fs 


Tapered folded plotes y 


Fig. 14 b. 


a. 


a. Segmented barrel dome 


c. Tapering folded plates 


a. Rotation about axis 


b. Translation along curve 


Doubly curved shell 


Fig. 16 


Fig. 15 


d. Pyramids 


ao. Taurus 


b. Parabolic 


. Elliptical 


Domes 


Fig. 17 


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either on the top or bottom of the shell. As such, it is 
not necessary that the complete dome be cast in one 
operation, and reuse of forms can be considered. For 
stability, opposite segments of the dome are constructed 
at the same time. 

The tapering barrel dome, shown in Fig. 15b, lends 
itself to many interesting variations. One well-known 
example is the intersecting vaults used for the Lambert- 
St. Louis Municipal Airport Building, St. Louis, Mo. 

The pyramid roof, shown in Fig. 15d, is limited in 
use mainly because thicknesses greater than 4 in. are 
required for spans exceeding 40 ft. Roughly, the thick- 
ness of the plate will generally be about 1 in. for every 
10 ft. of span if vertical beams are provided along the 
edges. 


DOUBLE CURVATURE SHELLS 


There is an infinite variety of doubly curved shells 
available to the architect. The two most prominent 
types, however, are shells formed by the rotation of a 
curve about an axis (Fig. 16a), and by the translation 
of a curve along another curve (Fig. 16b). 


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ROTATIONAL SHELLS 


The most common of the rotational shells is the 
spherical dome, which is formed by rotating a portion 
of a circular arc about an axis. Other curves, such as 
those shown in Fig. 17 in profile, can be employed to 
achieve different effects as well as satisfy varying plans. 

This type of shell is primarily used with continuous 
circular supports. Under these conditions a 4-in. shell is 
adequate for diameters up to and somewhat beyond 150 
ft., even for a shallow rise of one-tenth the diameter. 

Such shells are also suitable for isolated supported 
conditions. In this case, however, special attention must 
be given to adequate stiffening and reinforcement of the 
free edges. Partial domes, such as those used for band- 
Shells, also fall in this category. For partial domes, ribs 
are not needed along the vertical edges, except in those 
instances in which the span is large enough to cause 
excessive deflection of the edges. 


TRANSLATIONAL SHELLS 


Of the many types of shells, the translational form is 


_ Fig. 18 b. 


possibly the one best suited to the creation of a wide 
variety of free-form shapes with simple formwork. For 
example, when curvature along two perpendicular axes 
is in opposite directions, segments of this form can be 


combined to form the pleasing groined vault shown in 


Fig. 18a. Any combination of curvatures can be used, 
with the rise in one direction completely independent 
of the rise in the other direction. If the form is para- 
bolic, the surface can be described by a series of straight 
lines (Fig. 18a). 

When curvatures along the two axes are in the same 
direction, as in Fig. 18b, a dome rectangular in plan is 
achieved. Such a shape offers construction ease because 
the same profile occurs at all sections along the axis. 
Although not quite as apparent, the shells in Fig. 19 
fall into the same category. The edges of these shells all 
terminate along straight lines formed by the surface. 
Diamond-shaped as well as rectangular layouts are also 
possible. 


16 


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le 


Shells of this type use a minimum amount of material. 
In most cases, even with supports merely at the four 
corners, only mesh reinforcement is needed. Here again 
the thickness of the shell is dictated primarily by con- 
struction needs. 

The shells shown in Fig. 18 are particularly appro- 
priate for sizable spans, in excess of 80 ft., with almost 
square layouts and columns restricted to the corners. 
In both cases, that of the groined vault and the dome, 
stresses are compressive and quite small throughout the 


greater portion of the shell. For this reason, the rise of 


the dome in one direction need not exceed one-tenth 
of the span. Surprisingly economical domes can be 
achieved with a rise equal to one-fifteenth of the span. 

In the case of the groined vault, as mentioned before, 
ribs along the edges are not structurally necessary. For 
large spans, however, a small stiffening rib is often used 
to minimize deflection of the edges. The valley formed 
by the intersecting surfaces will generally be sufficiently 


Fig. 20 


stiff to render unnecessary ribs or undue thickness of 
the shell. 

For domed structures, supporting ribs are required 
at the edges. The ribs can be quite small, however, since 
they are subject mainly to axial forces from the dead 
load of the structure. 

Hyperbolic paraboloid surfaces, only a few of which 
are shown in Fig. 19, have proven to be very economical 
both in the use of material and in forming cost. Shells 
of the type shown in Fig. 19b have been built measuring 
60x60 ft. in plan, 114 in. thick and reinforced only with 
mesh reinforcement. To these advantages should be 
added the simplicity of formwork built from straight 
lumber. 

Hyperbolic paraboloid shells require slightly greater 
rise than other types of shells. As yet, the minimum rise 
that can be tolerated without causing undue deflection 
has not been determined. However, sufficient curvature 
is induced when the ratio of rise to the longest side is 


about one-eighth. In all cases, the value of ht/ab should 
in general not be less than 0.003, in which 

h=the rise 

t= thickness of shell 

a=one-half the length of the shell 

b=one-half the width of the shell 


Although not evident in Fig. 19, all of these shells 
require edge beams and sometimes ties to obtain satis- 
factory behavior. In the case of the inverted umbrella 
(Fig. 19b), the edge beam is in tension, and relatively 
small members are needed. On the other hand, the edge 
beams required for the three other shells may be in the 
range of 12x18-in. beams. For the inverted umbrella, 
an edge beam protruding above the shell will reduce 
deflection of the corners. For the other shells, the edge 
beams should extend below the shell. This is no un- 
violable rule, but where possible, such locations are de- 
sirable. 

Proper layout of other than the two simple arrange- 
ments of Figs. 19a and 19b requires additional study. 
For example, to assure proper behavior of the shell il- 
lustrated in Fig. 19d, it is imperative that the inter- 
section AB and CD be horizontal. A departure from the 
horizontal plane greatly weakens the shell by subjecting 
it to high bending forces. On the other hand, in Fig. 19c, 
line EF need not necessarily be horizontal. In making 
any layout beside the first two simple arrangements, an 
engineer should be consulted as early in the planning 
stages as possible. 

For preliminary purposes, a rather simple test can be 
applied to check the soundness of a shell roof layout. All 
of the edges in any quadrant are subject to either tensile 
or compressive axial forces, as in Fig. 20. Hence, any 
changes in the slope of the inter section from one quad- 
rant to the next require a reaction to change the direc- 
tion of the internal forces. This reaction can be supplied 
by acolumn at that point or by the two other perpendic- 
ular edges. When the latter scheme is employed, it is 
necessary to ascertain that the supporting edges can 
act as a truss transmitting the reaction to the column. 

For most conditions, the column supporting the shell 
need only support the vertical load. But not always, for 
in the case of the saddle shell pictured in Fig. 19a with 
the four edges completely unsupported, sufficient width 
must be supplied to the abutment to resist overturning 
due to unsymmetrical loads. 

There is another form of translational shell, illustrated 
in Fig. 21, that has been quite popular abroad. It has 
been used for long as well as short spans. Its merits lie 
chiefly in the reduction of formwork needed. In some 


cases, for spans under 100 ft., the shell has been precast 
and lifted into place. 

These shells are formed by translating a folded plate 
or small segment of an arc along a curved axis. In all 
instances the width of a segment is small compared to 
the span. Under this condition, the shell acts primarily 
as a deep arch. Thus, if a proper selection of shape is 
made for the arch, it will be subject primarily to axial 
forces. Since each segment is stable, formwork is needed 
for individual segments only. 

End supports are required for each segment because 
each shell acts primarily as an arch. To avoid bringing 


the roof down to a continuous abutment at ground level, 
a fan-type abutment is often used. While this scheme 
does not present a difficult structural problem, some of 
the abutment members must be large to handle the 
reaction forces concentrated in that region. 

As can be seen even in this cursory discussion, the 
span and load-carrying abilities of shells are virtually 
unlimited. The fancifully shaped shell roofs now appear- 
ing with ever-increasing frequency on the American con- 
struction scene are not only architecturally exciting and 
versatile; they also offer highly efficient use of the ma- 
terials involved. 


SHELLS GO TO WORK 


‘“‘Action is eloquence,’’ said Shakespeare. To 
this may be added the proviso, ‘‘if based on 
knowledge.’’ Concrete shells can speak elo- 
quently—if used knowledgeably—in a multitude 
of ways. Some of them are presented here. 


It is no longer news that shells offer an amazing choice 
of space shapes and spans. What is not as fully realized 
is that there are many freedoms in shell construction in 
addition to their shape and size versatility. Among the 
variables are the location of edge beams, type and color 
of roofing, choice of tie beams or diaphragms, and sur- 
face finish applied. Different approaches to these con- 
siderations can often produce markedly contrasting 
architectural effects in shells of basically similar shape 
and size. 

American architects have already embarked on an 
exploratory voyage aimed at discovering many of the 
limitless variations possible in shell work. Six projects 
in this country have been chosen at random to indicate 
a few of the areas in which architects can manipulate 
shell elements to produce a design precisely calculated 
to achieve its esthetic and service-dictated needs. 


BARRELS 
First National Bank 
Boulder, Colo. 
Architect: Hobart D. Wagener 
Boulder, Colo. 
Engineer: Ketchum & Konkel 
Denver, Colo. 


General contractor: Cys Construction Co. 
Boulder, Colo. 


Tradewell Market 
Burien, Wash. 
Architects: Welton Becket and Associates 
Los Angeles, Calif. 
Engineer: Richard Bradshaw 
Van Nuys, Calif. 


General contractor: Jentoft and Forbes 
Seattle, Wash. 


These two structures present quite different appear- 
ances even though both are roofed with long barrel shells 
of roughly the same span. Since the store sells food, it 


was created to afford an appetizingly open environment 
for display of the merchandise. The bank, on the other 
hand, aims at instilling confidence; this was achieved 
through a building both modern and substantial in ma- 
terials and proportions. 

To create the desired grace and symmetry for the 
store, the shells had to appear thin and allow for glazing 
up to their soffit. In addition, it was necessary that 
columns be thin and unobtrusive. By treating the edge 
beams as seemingly separate entities below the shell 
proper, the impression is given of barrels resting lightly 
on thin beams. Also the tiebeams are reduced to mere 
wires stretched between the column tops. On the ex- 
terior, they are concealed in the window transoms and 
in the interior they are painted the same color as the 
shells. Adding to the attractiveness of the building in 
general is the manner in which the roof line is treated. 
Longitudinally, the roof slants to a low point approxi- 
mately two-thirds the length of the building. The back 
one-third of the roof slants upward at a steeper angle 
than the front portion. The effect created is one of mo- 
tion and lightness. The shells are terminated along an 
inclined plane to produce a scalloped roof line. Since 
the barrels are cantilevered 12 ft. out over the loading 
area directly in front of the store, the total impression 
is of an informal welcome. 

A welcome is also manifest in the bank building, but 
it is one of greater formality aimed at inspiring respect 
and confidence. The barrels in this scheme were not 
meant to assume as dominant a role in the overall archi- 
tectural plan as in the store. Actually a small complex, 
these buildings are tied together by their use of con- 
trasting materials, and varied by different heights and 
roof lines. In addition to their usual duties of protection 
and decoration, these barrels perform an important 
third task. As has been mentioned in Clovis Heimsath’s 
article in this issue, a difficult problem facing architects 
handling groups of dissimilar buildings is choice of a 
connector. Ideally, the connector is a tie that springs 
spontaneously from one building and merges harmoni- 
ously with another. The barrel shells of the one-story 
portion of this bank relate it to its multistory neighbor 
in a manner both natural and effective. The shells also 
cover the walkway leading to the entrance doors and 
add flair to an otherwise severely rectangular structure. 
Since solid walls were desirable, ties were built into them. 
The barrels were terminated along a vertical plane to 
lead into the adjoining section of the building and also 
to reflect the lines of the structural frames despite the 
curvature of the shells themselves. 


BARREL SHELLS 


ee 


ile et 


Senior High School ‘‘U’’ No. 207 
Duval County, Fla. 


Architects: Hardwick & Lee 
Jacksonville, Fla. 


Engineer: Gomer E. Kraus 
Jacksonville, Fla. 


General contractor: Wesley of Florida, Inc. 
Jacksonville, Fla. 


Wayne Memorial High School 

Wayne, Mich. 
Architect-Engineer: Eberle M. Smith 
Associates, Inc., Detroit, Mich. 


General contractor: A. Z. Shmina & Sons Co. 


FOLDED PLATES Dearborn, Mich. 


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Even a shell as strongly rectilinear as the folded plate 
is adaptable to many floor plans in addition to those 
square or rectangular in outline. The circular auditorium 
at Wayne Memorial High School is roofed by a dozen 
pie-shaped folded plates that abut a central compression 
ring. Horizontal forces at the columns are controlled by 
a peripheral tension ring. The V-shaped tapered plates 
vary in thickness from 4 in. at the ridges to 51% in. at 
the valleys near the center and nearly 12 in. near the 
supports. This thickness variation and the cantilever 
of the plates several feet beyond the diaphragms tend 
to shift the center of gravity of the shell outward. The 
plates are thickened locally near the compression ring 
to reduce shear stresses and to provide room for the 
reinforcement. The roof, as well as its columns and can- 
crete masonry walls, forms a 12-sided polygonal audi- 
torium approximately 100 ft. in diameter that seats 939. 
Acoustically, the soffit of the roof sets up serratic sound 


patterns, and grille block walls covering the back half 
of the room lower the reverberation time to produce 
excellent sound properties. The result is an auditorium 
that is strikingly attractive and that has clear sight 
lines coupled with crystal-clear sonic qualities. 

Duval County’s new Senior High School illustrates 
the use of the popular truncated V-shaped folded plate 
roof for radial layout schools. This layout is a natural 
outgrowth of the campus-type school and, for small and 
medium size projects, offers the advantages of the 
campus with more strongly integrated parts. The class- 
room units, which radiate from the central multipurpose 
building, are roofed by folded plates with a 60 ft. clear 
span across the floor area. They also cantilever various 
distances to shade the windows, which vary in orienta- 
tion. The diagonal plates are pierced in some areas to 
provide supplemental clerestory lighting. 


HYPERBOLIC PARABOLOIDS 


24 


Zion Evangelical & Reformed Church 
- Milwaukee, Wis. 


Architect-Engineer: William P. Wenzler 
Milwaukee, Wis. 


General contractor: C. G. Schmidt, Inc. 
Milwaukee, Wis. 


Texas Instruments, Inc. 
Dallas, Texas 


Architects: O’Neil Ford and Richard Colley 
Associate Architect: A. B. Swank 
Associate Architect and Planner: S. B. Zisman 


General contractor: Robert E. McKee 
Dallas, Texas 


Special interest has been exhibited lately in the 
hyperbolic paraboloid, a shape of extraordinary versa- 
tility. Whether in a basic form or in one of the many 
combinations possible, the hyperbolic paraboloid affords 
a flexibility of space enclosure that is unrivaled. The 
Wisconsin Church and Texas industrial building illus- 
trate the manner in which it can be adapted to special- 
ized needs. Of course, such unusual projects are only 
part of the H/Pstory. The economy of the H/P isattested 
to by the number of times these roofs have been used 
for strictly utilitarian jobs such as reservoirs and ware- 
houses, on a first-cost basis alone. Bids for H/P roofs 


have frequently been lower than those for more con- 
ventional competing designs. 

Although shells are most often thought of in their 
role as roofs, they have frequently been used for founda- 
tions and, as in this church, they can also serve as partial 
walls for the structure. Six 20x30-ft. unsymmetrical 
shells join to frame the nave in a singularly compelling 
way. They arch over the floor area and forceably direct 
attention to the altar. Cast-in-place sections complete 
the roof and help stabilize the structure. Structural mul- 
lion frames, in which are set stained glass windows, fill 
the openings between the vertical planes of the shells. 
Lighting is calculated to highlight the undulating lines 
of the walls and roof and to emphasize the translucency 
of the windows. 


26 


7, 


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The shells were precast on the job site. This eliminated 
the need for the top forms that would have been neces- 
sary on the steep slopes of the shells if they had been 
cast in place. A 1%-in. layer of foamed polystyrene 
lined the forms and bonded with the concrete to 
serve the dual role of insulation and base for the plaster. 
Concrete was cast from the low points of the shell to- 
ward the high points to ensure good compaction. Two 
cranes, stationed on either side of the church, picked up 
each H/P section and raised it into place. Workmen 
then bolted the shells together opposite one another. 
The mullions were precast. The result was a simple and 
yet highly effective frame for a striking church. 

Contrasting both in occupancy and utilization of the 
H/P shape is the large industrial building. Termed by 


one architectural magazine as “‘a prototype of the new 
light, flexible industrial buildings,” it is an eloquent ex- 
ample of the freedom allowed by shell construction. The 
owner, an electronics research and manufacturing firm, 
commissioned a city planner to create a master five- 
year plan for a projected development to house its pre- 
cision machinery and highly skilled personnel. First unit 
of the plan is the building illustrated—a structure in- 
corporating shells and precast, prestressed components 
into an ideal environment for the fabrication of the com- 
pany’s product. The roof is composed of 42 units, each 
consisting of four identical hyperbolic paraboloid quad- 
rants combined to form horizontal ridges at the high 
points. These units, structurally independent of one 
another, provide 63-ft. square bays for maximum inte- 


rior flexibility. Equipment and people can be freely 
shifted to allow for new, improved flow patterns as de- 
velopments warrant. 

Another important design consideration was the ver- 
satility of the structure to adapt to expansion. It was 
realized that the initial construction would be adequate 
in floor area (3% acres) for a limited time only. Con- 
struction was recently completed on an addition that 
more than doubles the original size of the plant and in- 
creases the number of shells to 75 and the area covered 
to 296,675 sq.ft. Since the shells are structural entities 
unto themselves, the addition posed no problems of con- 
nection to the architect or engineer. 


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